Biomechanics of lower limb

Introduction to biomechanics

The study of biomechanics ranges from the inner workings of a cell to the movement and development of limbs, the vasculature, and bones. As we develop a greater understanding of the physiological behavior of living tissues, researchers are able to advance the field of tissue engineering, as well as develop improved treatments for a wide array of pathologies.

Biomechanics as a sports science, kinesiology, applies the laws of mechanics and physics to human performance in order to gain a greater understanding of performance in athletic events through modeling, simulation, and measurement.

Biomechanics

Biomechanics is the science concerned with the internal and external forces acting on the human body and the effects produced by these forces. At the highest levels of sports in which techniques play a major role, improvement comes so often from careful attention to detail that no coach can afford to leave these details to chance or guesswork. For such coaches knowledge of biomechanics might be regarded as essential

Continuum mechanics

It is often appropriate to model living tissues as continuous media. For example, at the tissue level, the arterial wall can be modeled as a continuum. This assumption breaks down when the length scales of interest approach the order of the microstructural details of the material. The basic postulates of continuum mechanics are conservation of linear and angular momentum, conservation of mass, conservation of energy, and the entropy inequality. Solids are usually modeled using "reference" or "Lagrangian" coordinates, whereas fluids are often modeled using "spatial" or "Eulerian" coordinates. Using these postulates and some assumptions regarding the particular problem at hand, a set of equilibrium equations can be established. The kinematics and constitutive relations are also needed to model a continuum.

Second and fourth order tensors are crucial in representing many quantities in biomechanics. In practice, however, the full tensor form of a fourth-order constitutive matrix is rarely used. Instead, simplifications such as isotropy, transverse isotropy, and incompressibility reduce the number of independent components. Commonly-used second-order tensors include the Cauchy stress tensor, the second Piola-Kirchhoff stress tensor, the deformation gradient tensor, and the Green strain tensor. A reader of the biomechanics literature would be well-advised to note precisely the definitions of the various tensors which are being used in a particular work.

Biomechanics of circulation

Under most circumstances, blood flow can be modeled by the Navier-Stokes equations. Whole blood can often be assumed to be an incompressible Newtonian fluid. However, this assumption fails when considering flows within arterioles. At this scale, the effects of individual red blood cells become significant, and whole blood can no longer be modeled as a continuum.

Biomechanics of the bones

Bones are anisotropic but are approximately transversely isotropic. In other words, bones are stronger along one axis than across that axis, and are approximately the same strength no matter how they are rotated around that axis.

The stress-strain relations of bones can be modeled using Hooke's Law, in which they are related by linear constants known as the Young's modulus or the elastic modulus, and the shear modulus and Poisson's ratio, collectively known as the Lamé constants. The constitutive matrix, a fourth order tensor, depends on the isotropy of the bone.

Muscle

There are three main types of muscles:

Skeletal muscle (striated): Unlike cardiac muscle, skeletal muscle can develop a sustained condition known as tetany through high frequency stimulation, resulting in overlapping twitches and a phenomenon known as wave summation. At a sufficiently high frequency, tetany occurs, and the contracticle force appears constant through

time. This allows skeletal muscle to develop a wide variety of forces. This muscle type can be voluntary controlled. Hill's Model is the most popular model used to study muscle.

Cardiac muscle (striated): Cardiomyocytes are a highly specialized cell type. These involuntarily contracted cells are located in the heart wall and operate in concert to develop synchronized beats. This is attributable to a refractory period between twitches.

Smooth muscle (smooth - lacking striations): The stomach, vasculature, and most of the digestive tract are largely composed of smooth muscle. This muscle type is involuntary and is controlled by the enteric nervous system.

Soft tissues

Soft tissues such as tendon, ligament and cartilage are combinations of matrix proteins and fluid. In each of these tissues the main strength bearing element is collagen, although the amount and type of collagen varies according to the function each tissue must perform. Elastin is also a major load-bearing constituent within skin, the vasculature, and connective tissues. The function of tendons is to connect muscle with bone and is subjected to tensile loads. Tendons must be strong to facilitate movement of the body while at the same time remaining compliant to prevent damage to the muscle tissues. Ligaments connect bone to bone and therefore are stiffer than tendons but are relatively close in their tensile strength. Cartilage, on the other hand, is primarily loaded in compression and acts as a cushion in the joints to distribute loads between bones. The compressive strength of cartilage is derived mainly from collagen as in tendons and ligaments, however because collagen is comparable to a "wet noodle" it must be supported by cross-links of glycosaminoglycans that also attract water and create a nearly incompressible tissue capable of supporting compressive loads.

Recently, research is growing on the biomechanics of other types of soft tissues such as skin and internal organs. This interest is spurred by the need for realism in the development of medical simulation.

Viscoelasticity

Viscoelasticity is readily evident in many soft tissues, where there is energy dissipation, or hysteresis, between the loading and unloading of the tissue during mechanical tests. Some soft tissues can be preconditioned by repetitive cyclic loading to the extent where the stress-strain curves for the loading and unloading portions of the tests nearly overlap. The most commonly used model for viscoelasticity is the Quasilinear Viscoelasticity theory (QLV). In addition, soft tissues exhibit other viscoelastic properties, including creep, stress relaxation, and preconditioning.

Kinematics

Kinematics is the branch of biomechanics concerned with the study of movement with reference to the amount of time taken to carry out the activity.

Distance and displacement

Distance and displacement are quantities used to describe the extent of a body's motion. Distance is the length of the path a body follows and displacement is the length of a straight line joining the start and finish points e.g. in a 400m race on a track the length of the path the athlete follows (distance) is 400m but their displacement will be zero metres (they finish where they start).

Speed and velocity

Speed and velocity describe the rate at which a body moves from one location to another. These two terms are often thought, incorrectly, to be the same. Average speed of a body is obtained by dividing the distance by the time taken where as the average Velocity is obtained by dividing the displacement by the time taken e.g. consider a swimmer in a 50m race in a 25m length pool who completes the race in 60 seconds - distance is 50m and displacement is 0m (swimmer is back where they started) so speed is 50/60= 0.83m/s and velocity is 0/60=0 m/s

Speed and Velocity = distance traveled ÷ time taken

Acceleration

Acceleration is defined as the rate at which velocity changes with respect to time.

average acceleration = (final velocity - initial velocity) ÷ elapsed time

From Newton's 2nd law:

Force = Mass x Acceleration Acceleration = Force ÷ Mass

If the mass of a sprinter is 70kg and the force exerted on the starting blocks is 700N then acceleration = 700 ÷ 70 = 10 msec²

Acceleration due to gravity

Whilst a body is in the air it is subject to a downward acceleration, due to gravity, of approximately 9.81m/s²

Vectors and scalars

Distance and speed can be described in terms of magnitude and are known as scalars. Displacement, velocity and acceleration that require magnitude and direction are known as vectors.

Components of a vector

Figure 1Figure 2

Let us consider the horizontal and vertical components of velocity of the shot in Figure 1.

Figure 2 indicates the angle of release of the shot at 35° and the velocity at release as 12 m/sec.

Vertical component Vv = 12 x sin 35° = 6.88 m/sec Horizontal component Vh = 12 x cos 35° = 9.82 m/sec

Let us now consider the distance the shot will travel horizontally (its displacement).

Range (R) = ((v² × sinØ × cosØ) + (v × cosØ × sqrt((v × sinØ)² + 2gh))) ÷ g

Where v = 12, Ø = 35, h = 2m (height of the shot above the ground at release) and g = 9.81

R = ((12² × sin35 × cos35) + (12 × cos35 × sqrt((12 × sin35)² + 2x9.81x2))) ÷ 9.81 R = 16.22m

The time of flight of the shot can be determined from the equation:

Time of flight = Distance (R) ÷ velocity (Vh) Time of flight = 16.22 ÷ 9.82 = 1.65 seconds

Uniformly accelerated motion

When a body experiences the same acceleration throughout some interval of time, its acceleration is said to be constant or uniform. In these circumstances, the following equations apply:

Final velocity = initial velocity + (acceleration x time) Distance = (initial velocity x time) + (½ x acceleration x time²)

Moment of force (torque)

The moment of force or torque is defined as the application of a force at a perpendicular distance to a joint or point of rotation.

Angular Kinematics

Angular distance and displacement

When a rotating body moves from one position to another, the angular distance through which it moves is equal to the length of the angular path. The angular displacement that a rotating body experiences is equal in magnitude to the angle between the initial and final position of the body.

Angular movement is usually expressed in radians where 1 radian = 57.3°

Angular speed, velocity and acceleration Angular speed = angular displacement ÷ time Angular velocity = angular displacement ÷ time

Angular acceleration = (final angular velocity - initial angular velocity) ÷ time

Angular Momentum

Angular momentum is defined as: angular velocity x moment of inertia

The angular momentum of a system remains constant throughout a movement provided nothing outside the system acts with a turning moment on it. This is known as the Law Conservation of Angular Momentum. In simple terms, this means that if a skater, when already spinning, changes their moment of inertia (they move their arms out to the side) then the rate of spin will change but the angular momentum will stay the same.

Linear Kinetics

Kinetics is concerned with what causes a body to move the way it does.

Momentum, inertia, mass, weight and force Momentum: mass x velocity Inertia: the resistance to acceleration - reluctance of a body to change whatever it is doing

Mass: the quantity of matter of which a body is composed of - not affected by gravity - measured in kilograms (kg)

Weight: force due to gravity - is mass x gravity (9.81m/s²)

Force: a pushing a pulling action that causes a change of state (rest/motion) of a body - is proportional to mass x acceleration - is measured in Newtons (N) where 1N is the force that will produce an acceleration of 1 m/s² in a body of 1kg mass

The classification of forces, external or internal, depends on the definition of the 'system'. In biomechanics, the body is seen as the 'system' so any force exerted by one part of the system on another is known as an internal force all other forces are external.

Newton's Laws of Motion First Law: Every body continues in its state of rest or motion in a straight line unless compelled to change that

state by external forces exerted upon it. Second Law: The rate of change of momentum of a body is proportional to the force causing it and the change

takes place in the direction in which the force acts

Third Law: To every action there is an equal and opposite reaction OR for every force that is exerted by one body on another there is an equal and opposite force exerted by the second body on the first

Newton's law of gravitation Any two particles of matter attract one another with a force directly proportional to the product of their masses and

inversely proportional to the square of the distance between them

Work, Energy and Power

Kinetic energy is mechanical energy possessed by any moving object. An equation for Kinetic Energy can be derived from the work definition:

Work = force x distance moved in the direction of the force

Kinetic Energy = ½ x mass x velocity² (result is in joules)

Power is defined as the rate at which energy is used or created from other forms

Power = energy used ÷ time taken Power = (force x distance) ÷ time taken

Power = force x velocity

Angular Kinetics

Translation and couple

A force that acts through the centre of a body result in only translation. A force whose line of action does not pass through the body's centre of gravity is called an eccentric force and results in translation and rotation.

Example - if you push through the centre of an object it will move forward in the direction of the force (translation) if you push to one side of the object (eccentric force) it will move forward and rotate.

A couple is an arrangement of two equal and opposite forces that cause a body to rotate.

s

A lever is a rigid structure, hinged at one point and to which forces are applied at two other points. The hinge or pivot point is known as the fulcrum. One of the forces that act on the lever is known as the weight that opposes movement and the other is the force that causes movement. For more details see the page on Levers.

Bernoulli Effect

Lift forces interact with objects in flight and are caused by the aerodynamic shape of the object. If an object has a curved top and flat bottom (wing of an aircraft), the air will have further to travel over the top than the bottom. For the two airflows to reach the back of the object at the same time the air flowing over the top of the object will have to flow faster. This means that there will be less pressure above the object (air is thinner) than below it and the object will lift. This is often referred to as the Bernoulli effect.

Introduction to hip joint anatomy

The hip joint is a ball and socket joint, formed by the head of the Femur (thigh bone) and the acetabulum of the pelvis. The dome-shaped head of the femur forms the ball, which fits snuggly into the concave socket of the acetabulum. The hip joint is a very sturdy joint, due to the tight fitting of the bones and the strong surrounding ligaments and muscles

Understanding how the different layers of the hip are built and connected can help you understand how the hip works, how it can be injured, and how challenging recovery can be when this joint is injured. The deepest layer of the hip includes the bones and the joints. The next layer is made up of the ligaments of the joint capsule. The tendons and the muscles come next.

ANATOMY

Anatomy:

The important structures of the hip can be divided into several categories. These include

bones and joints ligaments and tendons

muscles

nerves

blood vessels

bursae

Bones of the hip joint

The femur is the longest bone in the body which forms the thigh. The part which articulates with the pelvis to form the hip joint is known as the head of the femur. This is a round, dome shaped protrusion. Close to the top of the femur are two other protrusions, known as the greater and lesser trochanters. The main function of the trochanters is for muscle attachment.

The pelvis is actually two large bones which connect at the front by the pubis symphesis (a cartilage disc) and at the back by the Sacrum. The Sacrum is part of the spine and consists of 4 fused vertebrae which do not move independently of one another. The joints formed by either side of the Sacrum and the two pelvic bones are the Sacroiliac joints (SIJ).

The surfaces of both the head of the femur and the acetabulum are covered with a thin layer of hyaline cartilage which acts to allow smooth movement of the joint.

Bones and Joints

The bones of the hip are the femur (the thighbone) and the pelvis. The top end of the femur is shaped like a ball. This ball is called the femoral head. The femoral head fits into a round socket on the side of the pelvis. This socket is called the acetabulum.

The femoral head is attached to the rest of the femur by a short section of bone called the femoral neck. A large bump juts outward from the top of the femur, next to the femoral neck. This bump,

called the greater trochanter, can be felt along the side of your hip. Large and important muscles connect to the greater trochanter. One muscle is the gluteus medius. It is a key muscle for keeping the pelvis level as you walk.

Articular cartilage is the material that covers the ends of the bones of any joint. Articular cartilage is about one-quarter of an inch thick in the large, weight-bearing joints like the hip. Articular cartilage is white and shiny and has a rubbery consistency. It is slippery, which allows the joint surfaces to slide against one another without causing any damage. The function of articular cartilage is to absorb shock and provide an extremely smooth surface to make motion easier. We have articular cartilage essentially everywhere that two bony surfaces move against one another, or articulate.

In the hip, articular cartilage covers the end of the femur and the socket portion of the acetabulum in the pelvis. The cartilage is especially thick in the back part of the socket, as this is where most of the force occurs during walking and running.

Articulation

The hip joint is a synovial joint formed by the articulation of the rounded head of the femur and the cup-like acetabulum of the pelvis. It forms the primary connection between the bones of the lower limb and the axial skeleton of the trunk and pelvis. Both joint surfaces are covered with a strong but lubricated layer called articular hyaline cartilage. The cuplike acetabulum forms at the union of three pelvic bones — the ilium, pubis, and ischium.[5] The Y-shaped growth plate that separates them, the triradiate cartilage, is fused definitively at ages 14-16.[6] It is a special type of spheroidal or ball and socket joint where the roughly spherical femoral head is largely contained within the acetabulum and has an average radius of curvature of 2.5 cm.[7] The acetabulum grasps almost half the femoral ball, a grip augmented by a ring-shaped fibrocartilaginous lip, the acetabular labrum, which extends the joint beyond the equator.[5] The head of the femur is attached to the shaft by a thin neck region that is often prone to fracture in the elderly, which is mainly due to the degenerative effects of osteoporosis.

Transverse and sagittal angles of acetabular inlet plane.

The acetabulum is oriented inferiorly, laterally and anteriorly, while the femoral neck is directed superiorly, medially, and anteriorly.

The transverse angle of the acetabular inlet can be determined by measuring the angle between a line passing from the superior to the inferior acetabular rim and the horizontal plane; an angle which normally measures 51° at birth and 40° in adults, and which affects the acetabular lateral coverage of the femoral head and several other parameters. The sagittal angle of the acetabular inlet measures 7° at birth and increases to 17° in adults. [8]

Femoral neck angle

The angle between the longitudinal axes of the femoral neck and shaft, called the caput-collum-diaphyseal angle or CCD angle, normally measures approximately 150° in newborn and 126° in adults (coxa norma).[9] An abnormally small angle is known as coxa vara and an abnormally large angle as coxa valga. Because changes in shape of the femur naturally affects the knee, coxa valga is often combined with genu varum (bow-leggedness), while coxa vara leads to genu valgum (knock-knees). [10]

Changes in trabecular patterns due to altered CCD angle. Coxa valga leads to more compression trabeculae, coxa vara to more tension trabeculae.[9]

Changes in CCD angle is the result of changes in the stress patterns applied to the hip joint. Such changes, caused for example by a dislocation, changes the trabecular patterns inside the bones. Two continuous trabecular systems emerging on auricular surface of the sacroiliac joint meander and criss-cross each other down through the hip bone, the femoral head, neck, and shaft.

In the hip bone, one system arises on the upper part of auricular surface to converge onto the posterior surface of the greater sciatic notch, from where its trabeculae are reflected to the inferior part of the acetabulum. The other system emerges on the lower part of the auricular surface, converges at the level of the superior gluteal line, and is reflected laterally onto the upper part of the acetabulum.

In the femur, the first system lines up with a system arising from the lateral part of the femoral shaft to stretch to the inferior portion of the femoral neck and head. The other system lines up with a system in the femur stretching from the medial part of the femoral shaft to the superior part of the femoral head. [11]

On the lateral side of the hip joint the fascia lata is strengthened to form the iliotibial tract which functions as a tension band and reduces the bending loads on the proximal part of the femur.[9]

Bursae

Where friction occurs between muscles, tendons, and bones there is usually a structure called a bursa. A bursa is a thin sac of tissue that contains fluid to lubricate the area and reduce friction. The bursa is a normal structure. The body will even produce a bursa in response to friction.

Think of a bursa like this. If you press your hands together and slide them against one another, you produce some friction. In fact, when your hands are cold you may rub them together briskly to create heat from the friction. Now imagine that you hold in your hands a small plastic sack that contains a few drops of salad oil. This sack would let your hands glide freely against each other without a lot of friction.

A bursa that sometimes causes problems in the hip is sandwiched between the bump on the outer hip (the greater trochanter) and the muscles and tendons that cross over the bump. This bursa, called the greater trochanteric bursa, can get irritated if the iliotibial band (discussed earlier) is tight. Another bursa sits between the iliopsoas muscle where it passes in front of the hip joint. Bursitis here is called iliopsoas bursitis. A third bursa is over the ischial tuberosity, the bump of bone in your buttocks that you sit on.>

Capsule

The capsule attaches to the hip bone outside the acetabular lip which thus projects into the capsular space. On the femoral side, the distance between the head's cartilaginous rim and the capsular attachment at the base of the neck is constant, which leaves a wider extracapsular part of the neck at the back than at the front [12]. [13] The strong but loose fibrous capsule of the hip joint permits the hip joint to have the second largest range of movement (second only to the shoulder) and yet support the weight of the body, arms and head.

The capsule has two sets of fibers: longitudinal and circular.

The circular fibers form a collar around the femoral neck called the zona orbicularis. The longitudinal retinacular fibers travel along the neck and carry blood vessels.

Ligaments of the hip joint

The stability of the hip owes greatly to the presence of its ligaments.

1. Iliofemoral ligament: This is a strong ligament which connects the pelvis to the femur at the front of the joint. It resembles a Y in shape and stabilises the hip by limiting hyperextension

2. Pubofemoral ligament: The pubofemoral ligament attaches the part of the pelvis known as the pubis (most forward part, either side of the pubic symphesis) to the femur

3. Ischiofemoral ligament: This is a ligament which reinforces the posterior aspect of the capsule, attaching to the ischium and between the two trochanters of the femur.

Ligaments and Tendons

There are several important ligaments in the hip. Ligaments are soft tissue structures that connect bones to bones. A joint capsule is a watertight sac that surrounds a joint. In the hip, the joint capsule is formed by a group of three strong ligaments that connect the femoral head to the acetabulum. These ligaments are the main source of stability for the hip. They help hold the hip in place.

A small ligament connects the very tip of the femoral head to the acetabulum. This ligament, called the ligamentum teres, doesn't play a role in controlling hip movement like the main hip ligaments. It does, however, have a small artery within the ligament that brings a very small blood supply to part of the femoral head.

A long tendon band runs alongside the femur from the hip to the knee. This is the iliotibial band. It gives a connecting point for several hip muscles. A tight iliotibial band can cause hip and knee problems.

A special type of ligament forms a unique structure inside the hip called the labrum. The labrum is attached almost completely around the edge of the acetabulum. The shape and the way the labrum is attached create a deeper cup for the acetabulum socket. This small rim of cartilage can be injured and cause pain and clicking in the hip.

Labrum of the hip joint

Just like the ball and socket joint of the shoulder, the hip joint has a labrum. This is a circular layer of cartilage which surrounds the outer part of the acetabulum effectively making the socket deeper and so helping provide more stability. Labrum tears are a common injury to the hip joint.

Muscle Groups surrounding the hip joint

There are numerous muscles which attach to or cover the hip joint:

Gluteals: Gluteus Maximus, Gluteus Minimus and Gluteus Medius are the three muscles referred to as the gluteals. They all attach to the posterior surface of the large flat area of the pelvis (Ilium) and travel laterally to insert into the greater trochanter of the femur. Medius and Minimus are responsible for abducting and medially rotating the hip joint, as well as stabilising the pelvis. Gluteus maximus extends and laterally rotates the hip joint.

Quadriceps: The four Quadricep muscles (Vastus lateralis, medialis, intermedius and Rectus femoris) all attach inferiorly to the tibial tuberosity of the shin. Rectus femoris originates at the Anterior Inferior Iliac Spine (AIIS - protrusion at the front of the ilium) and acts to flex the hip. The 3 other Quad muscles do not cross the hip joint, and attach around the greater trochanter and just below it.

Iliopsoas: The is the primary hip flexor muscle which consists of 3 parts. Together they attach superiorly to the lower part of the spine and the inside of the ilium (flat upper part of the pelvis). They then cross the hip joint and insert to the lesser trochanter of the femur.

Hamstrings: The hamstrings are three muscles which form the back of the thigh. They all attach superiorly to the ischial tuberosity (lowest part of the pelvis, sometimes referred to as the sitting bone!) and cause hip extension.

Groin muscles: There are three main groin muscles, which are anatomically termed the adductor muscles. They all attach superiorly to the pubis and travel down the inside of the thigh. Their action is hip adduction.

The hip is surrounded by thick muscles. The gluteals make up the muscles of the buttocks on the back of the hip. The inner thigh is formed by the adductor muscles. The main action of the adductors is to pull the leg inward toward the other leg. The

muscles that flex the hip are in front of the hip joint. These include the iliopsoas muscle. This deep muscle begins in the low back and pelvis and connects on the inside edge of the upper femur. Another large hip flexor is the rectus femoris. The rectus femoris is one of the quadriceps muscles, the largest group of muscles on the front of the thigh. Smaller muscles going from the pelvis to the hip help to stabilize and rotate the hip.

Finally, the hamstring muscles that run down the back of the thigh start on the bottom of the pelvis. Because the hamstrings cross the back of the hip joint on their way to the knee, they help to extend the hip, pulling it backwards.

Nerves

All of the nerves that travel down the thigh pass by the hip. The main nerves are the femoral nerve in front and the sciatic nerve in back of the hip. A smaller nerve, called the obturator nerve, also goes to the hip.

These nerves carry the signals from the brain to the muscles that move the hip. The nerves also carry signals back to the brain about sensations such as touch, pain, and temperature.

Blood Vessels

Traveling along with the nerves are the large vessels that supply the lower limb with blood. The large femoral artery begins deep within the pelvis. It passes by the front of the hip area and goes down toward the inner edge of the knee. If you place your hand on the front of your upper thigh you may be able to feel the pulsing of this large artery.

The femoral artery has a deep branch, called the profunda femoris (profunda means deep). The profunda femoris sends two vessels that go through the hip joint capsule. These vessels are the main blood supply for the femoral head. As mentioned earlier, the ligamentum teres contains a small blood vessel that gives a very small supply of blood to the top of the femoral head.

Other small vessels form within the pelvis and supply the back portion of the buttocks and hip.

Movement:

The movements of the hip joint is thus performed by a series of muscles which are here presented in order of importance [18]

with the range of motion from the neutral zero-degree position[17] indicated:

Lateral or external rotation (30° with the hip extended, 50° with the hip flexed): gluteus maximus; quadratus femoris; obturator internus; dorsal fibers of gluteus medius and minimus; iliopsoas (including psoas major from the vertebral column); obturator externus; adductor magnus, longus, brevis, and minimus; piriformis; and sartorius.

Medial or internal rotation (40°): anterior fibers of gluteus medius and minimus; tensor fascia latae; the part of adductor magnus inserted into the adductor tubercle; and, with the leg abducted also the pectineus.

Extension or retroversion (20°): gluteus maximus (if put out of action, active standing from a sitting position is not possible, but standing and walking on a flat surface is); dorsal fibers of gluteus medius and minimus; adductor magnus; and piriformis. Additionally, the following thigh muscles extend the hip: semimembranosus, semitendinosus, and long head of biceps femoris.

Flexion or anteversion (140°): iliopsoas (with psoas major from vertebral column); tensor fascia latae, pectineus, adductor longus, adductor brevis, and gracilis. Thigh muscles acting as hip flexors: rectus femoris and sartorius.

Abduction (50° with hip extended, 80° with hip flexed): gluteus medius; tensor fascia latae; gluteus maximus with its attachment at the fascia lata; gluteus minimus; piriformis; and obturator internus.

Adduction (30° with hip extended, 20° with hip flexed): adductor magnus with adductor minimus; adductor longus, adductor brevis, gluteus maximus with its attachment at the gluteal tuberosity; gracilis (extends to the tibia); pectineus, quadratus femoris; and obturator externus. Of the thigh muscles, semitendinosus is especially involved in hip adduction.

Hip Joint

The hip joint has the following normal ranges of movement: Flexion, Extension, Adduction, Abduction, Medial Rotation and Lateral Rotation.

Planes and Axes

Joint actions are described in relation to the anatomical position. Movement is defined by referring to the three planes and the three axis. (see diagram below)

The Three Planes

Sagittal Plane - a vertical plane which passes from front to rear dividing the body into two symmetrical halves

Frontal Plane - which passes from side to side at right angles to the sagittal plane

Transverse Plane - any horizontal plane which is parallel to the diaphragm

The Three Axis

Frontal Axis - passes horizontally

from side to side at right angles to the sagittal plane

Sagittal Axis - passes from front to rear lying at right angles to the frontal plane

Longitudinal Axis - passes from head to foot at right angles to the transverse plane

HIP JOINT BIOMECHANICS

A 3D model of the hip and surrounding soft tissue has been developed and is being used to investigate the effects of implant geometry on muscle and joint reaction forces. The indeterminate system of mechanical equations was solved by assuming that the body selects muscle forces in a way which minimises some measure of effort or work. Nonlinear optimisation criteria are known to give better results, but have been considered too complex and time consuming to apply on a large scale. An algorithm has been developed to apply such a criterion efficiently so that a large number of geometries could be investigated.

Changes in force with geometry are significant. An F.E. model of the construct (bone and implant) is being used to study the effects of changing force on stress, strain and related quantities.

Introduction to knee joint anatomy

The knee joint is the largest joint in the body, consisting of 4 bones and an extensive network of ligaments and muscles. Injuries to the knee joint are amongst the most common in sporting activities and understanding the anatomy of the joint is fundamental in understanding any subsequent pathology

To better understand how knee problems occur, it is important to understand some of the anatomy of the knee joint and how the parts of the knee work together to maintain normal function.

First, we will define some common anatomic terms as they relate to the knee. This will make it clearer as we talk about the structures later.

Many parts of the body have duplicates. So it is common to describe parts of the body using terms that define where the part is in relation to an imaginary line drawn through the middle of the body. For example, medial means closer to the midline. So the medial side of the knee is the side that is closest to the other knee. The lateral side of the knee is the side that is away from the other knee. Structures on the medial side usually have medial as part of their name, such as the medial meniscus. The term anterior refers to the front of the knee, while the term posterior refers to the back of the knee. So the anterior cruciate ligament is in front of the posterior cruciate ligament.

Important Structures

The important parts of the knee include

bones and joints ligaments and tendons

muscles

nerves

blood vessels

Bones and Joints

The knee is the meeting place of two important bones in the leg, the femur (the thighbone) and the tibia (the shinbone). The patella (or kneecap, as it is commonly called) is made of bone and sits in front of the knee.

The knee joint is a synovial joint. Synovial joints are enclosed by a ligament capsule and contain a fluid, called synovial fluid, that lubricates the joint.

The end of the femur joins the top of the tibia to create the knee joint. Two round knobs called femoral condyles are found on the end of the femur. These condyles rest on the top surface of the tibia. This surface is called the tibial plateau. The outside half (farthest away from the other knee) is called the lateral tibial plateau, and the inside half (closest to the other knee) is called the medial tibial plateau.

The patella glides through a special groove formed by the two femoral condyles called the patellofemoral groove.

The smaller bone of the lower leg, the fibula, never really enters the knee joint. It does have a small joint that connects it to the side of the tibia. This joint normally moves very little.

Articular cartilage is the material that covers the ends of the bones of any joint. This material is about one-quarter of an inch thick in most large joints. It is white and shiny with a rubbery consistency. Articular cartilage is a slippery substance that allows the surfaces to slide against one another without damage to either surface. The function of articular cartilage is to absorb shock and provide an extremely smooth surface to facilitate motion. We have articular cartilage essentially everywhere that two bony surfaces move against one another, or articulate. In the knee, articular cartilage covers the ends of the femur, the top of the tibia, and the back of the patella.

This is a hinge type of synovial joint that permits some rotation. Its structure is complicated because it consists of three articulations: an intermediate one between the patella

and femur and lateral and medial ones between the femoral and tibial condyles.

Articular Surfaces of the Knee Joint

The bones involved are the femur, tibia, and patella. The articular surfaces are the large curved condyles of the femur, the flattened condyles of the tibia, and the

facets of the patella.

The knee joint is relatively weak mechanically because of the configurations of its articular surfaces. It relies on the ligaments that bind the femur to the tibia for strength.

On the superior surface of each tibial condyle, there is an articular area for the corresponding femoral condyle.

These areas, commonly referred to as the medial and lateral tibial plateaux, are separated from each other by a narrow, nonarticular area, which widens anteriorly and posteriorly into anterior and posterior intercondylar areas, respectively.

Surface Anatomy of the Knee Joint

This joint may be felt as a slight gap on each side between the corresponding femoral and tibial condyles. When the leg is flexed or extended, a depression appears on each side of the patellar ligament.

The articular capsule is very superficial in these depressions. The knee joint lies deep to the apex of the patella.

Movements of the Knee Joint

The principal movements occurring at this joint are flexion and extension of the leg, but some rotation also occurs in the flexed position.

Flexion and extension of the knee joint are very free movements.

Flexion normally stops when the calf contacts the thigh. The ligaments of the knee stop extension of the leg.

When the knee is fully extended, the skin anterior to the patella is loose and can easily be picked up. This laxity of the skin helps flexion to occur.

The knee "locks" owing to medial rotation of the femur on the tibia. This makes the lower limb a solid column and more adapted for weight bearing. To "unlock" the knee the popliteus muscle contracts, thereby rotating the femur laterally so that flexion of the knee can occur.

The Articular Capsule of the Knee

The fibrous capsule is strong, especially where local thickenings of it form ligaments.

Superiorly, the fibrous capsule is attached to the femur, just proximal to the articular margins of the condyles and to the intercondylar line posteriorly.

It is deficient on the lateral condyle, which allows the tendon of the popliteus muscle to pass out of the joint and insert into the tibia.

Inferiorly the fibrous capsule is attached to the articular margin of the tibia, except where the tendon of the popliteus muscle crosses the bone.

Here the fibrous capsule is prolonged inferolaterally over the popliteus to the head of the fibula, forming the arcuate popliteal ligament.

The fibrous capsule is supplemented and strengthened by five intrinsic ligaments; patellar ligament, fibular collateral ligament, tibial collateral ligament, oblique popliteal ligament, and arcuate popliteal ligament.

These are often called the external ligaments to differentiate them from the internal ligaments (e.g., the cruciate ligaments, which are internal to the fibrous capsule).

The Patellar Ligament or Ligamentum Patellae

This very strong, thick band is the continuation of the tendon of the quadriceps femoris muscle.

The patella is a sesamoid bone in this tendon. The patella is continuous with the fibrous capsule of the knee joint and is most easily felt when the leg is extended.

The superior part of its deep surface is separated from the synovial membrane of the knee joint by a mass of loose fatty tissue called the infrapatellar fatpad. The inferior part of the patellar ligament is separated from the anterior surface of the tibia by the deep infrapatellar bursa.

Patellar Reflex

With the leg flexed, the patellar ligament is struck to elicit a knee jerk. This patellar reflex or knee reflex results in the extension of the leg. This reflex is blocked by damage to the femoral nerve, which supplies the quadriceps muscle. Similarly, damage to the reflex centres in the spinal cord (L2, L3, and L4) will affect the patellar reflex.

The Fibular Collateral Ligament

The fibular collateral ligament (lateral ligament) is a round pencil-like cord about 5 cm long.

It extends inferiorly from the lateral epicondyle of the femur to the lateral surface of the head of the fibula.

The tendon of the popliteus muscle passes deep to the fibular collateral ligament , separating it from the lateral meniscus.

The biceps femoris muscle is also split into two parts by this ligament.

The fibular collateral ligament is fused with the fibrous capsule of the knee joint superiorly ; hence, this part of it is an intrinsic ligament.

Inferiorly the fibular collateral ligament is separated from the fibrous capsule by fatty tissue; hence this part of it is an extrinsic ligament.

The Tibial Collateral Ligament

This ligament (also known as the medial ligament) is a strong, flat band, 8 to 9 cm long, which extends from the medial epicondyle of the femur to the medial condyle and superior part of the medial surface of the tibia.

It is a thickening of the fibrous capsule of the knee joint and is partly continuous with the tendon of the adductor magnus muscle.

The medial inferior genicular vessels and nerve separate the inferior end of the ligament from the tibia.

The deep fibres of the tibial collateral ligament are firmly attached to the medial meniscus and the fibrous capsule of the knee.

Injuries, the collateral ligaments and the knee joint

The tibial and fibular collateral ligaments normally prevent disruption of the sides of the knee joint. They are tightly stretched when the leg is extended and prevent the rotation of the tibia laterally or the femur

medially.

As the collateral ligaments are slack during flexion of the leg, they permit some rotation of the tibia on the femur in this position.

The fibular collateral ligament is not commonly torn because it is very strong. However, lesions (e.g., strains or tears) or the fibular collateral ligament can have serious consequences.

Usually, it is the distal end of the ligament that tears, and sometimes the head of the fibular is pulled off because the ligament is stronger than the bone. Complete tears are associated with stretching of the common fibular (peroneal) nerve. This affects the muscles of the anterior and lateral compartments of the leg and may produce foot-drop owing to paralysis of the dorsiflexor and eversion muscles of the foot.

The firm attachment of the tibial collateral ligament to the medial meniscus is of considerable clinical significance because injury to the tibial collateral ligament frequent results in concomitant injury to the medial meniscus.

Rupture of the tibial collateral ligament, often associated with tearing of the medial meniscus and anterior cruciate ligament, is a common type of football injury. The damage is frequently caused by a blow to the lateral side of the knee.

When considering soft tissue injuries of the knee, always think of the three Cs which indicate those structures that may be damaged: Collateral ligaments, Cruciate ligaments, and Cartilage (menisci).

The Oblique Popliteal Ligament

The broad band is an expansion of the tendon of the semimembranosus muscle. The oblique popliteal ligament strengthens the fibrous capsule of the knee joint posteriorly.

It arises posterior to the medial epicondyle of the tibia and passes superolaterally to attach to the central part of the posterior aspect of the fibrous capsule of the knee joint.

The Arcuate Popliteal Ligament

This Y-shaped band of fibres also strengthens the fibrous capsule posteriorly. The stem of the ligament arises from the posterior aspect of the head of the fibula. As it passes superomedially over the tendon of the popliteus muscle, the arcuate popliteal ligament spreads out over the posterior surface of the knee joint.

It inserts into the intercondylar area of the tibia and the posterior aspect of the lateral epicondyle of the femur.

Cruciate Ligaments of the Knee Joint

These are very strong ligaments within the capsule of the joint but are outside the synovial cavity.

Joining the femur and tibia, they are located between they are located between the medial and lateral condyles and are separated from the joint cavity by the synovial membrane. The synovial capsule lines the fibrous capsule, except posteriorly where it is reflected anteriorly around the cruciate ligaments.

The cruciate (L. resembling a cross) ligaments are strong, rounded bands that cross each other obliquely in a manner similar to an X. They are named anterior and posterior according to their site of attachment to the tibia, i.e., the anterior cruciate ligament attaches to the tibia anteriorly and the posterior cruciate ligament attaches to it posteriorly. These ligaments are essential to the anteroposterior stability of the knee joint, especially when it is flexed.

The Anterior Cruciate Ligament

The weaker of the two ligaments, the anterior cruciate ligament arises from the anterior part of the intercondylar area of the tibia, just posterior to the attachment of the medial meniscus.

It extends superiorly, posteriorly, and laterally to attach to the posterior part of the medial side of the lateral condyle of the femur.

The anterior cruciate ligament, which is slack when the knee is flexed and taut when it is fully extended, prevents posterior displacement of the femur on the tibia hyperextension of the knee joint. When the joint is flexed at a right angle, the tibia cannot be pulled anteriorly because it is held by the anterior cruciate ligament.

The Posterior Cruciate Ligament

This is the stronger of the two ligaments. It arises from the posterior part of the intercondylar area of the tibia and passes superiorly and anteriorly on the medial side of the anterior cruciate ligament to attach to the anterior part of the lateral surface of the medial condyle of the femur.

The posterior cruciate ligament is the first structure observed when the knee joint is surgically opened posteriorly.

The posterior cruciate ligament, which tightens during flexion of the knee joint, prevents anterior displacement of the femur on the tibia or posterior displacement of the tibia.

It also helps to prevent hyperflexion of the knee joint. In the weight bearing flexed knee, it is the main stabilising factor for the femur, e.g., when walking downhill or downstairs.

The Menisci of the Knee Joint

The medial and lateral menisci (G. crescents) are crescentic plates of fibrocartilage on the articular surface of the tibia.

These act like shock absorbers. Because they are basically C-shaped, they were formally called semilunar cartilages. They are wedge-shaped in the transverse section.

The menisci are firmly attached at their ends to the intercondylar area of the tibia. The menisci deepen the articular surfaces of the tibia where they articulate with the femoral condyles.

Their superior surfaces are slightly concave for reception of their condyles, whereas their inferior surfaces that rest on the tibial condyles are flatter.

The menisci are thick at their peripheral attached margins and thin at their internal unattached edges.

Being smooth and slightly movable, the menisci fill the gaps between the femur and tibia that would otherwise be present during movements of the knee joint. Their external margins are attached to the fibrous capsule of the knee joint and through it to the edges of the articular surfaces of the tibia.

The capsular fibres that attach the thick, convex margins of the menisci to the tibial condyles are called coronary ligaments.

A slender fibrous band, called the transverse ligament of the knee, joins the anterior edges of the two menisci. This connection allows them to move together during movements of the femur on the tibia. The thickness of this ligament varies in different people; sometimes it is absent.

The thick peripheral margins of the menisci are vascularised by genicular branches of the popliteal artery, but the thin unattached edges of the interior of the joint are avascular.

The Medial Meniscus

This C-shaped cartilage is broader posteriorly than anteriorly.

Its anterior end or horn (L. cornu) is attached to the anterior intercondylar area of the tibia, anterior to the attachment of the anterior cruciate ligament.

The posterior end or horn is attached to the posterior intercondylar area, anterior to the attachment of the posterior cruciate ligament and between the attachments of the lateral meniscus and the posterior cruciate ligament.

The medial meniscus is firmly attached to the deep surface of the tibial collateral ligament.

The Lateral Meniscus

This C-shaped cartilage is nearly circular and conforms to the rather circular lateral tibial condyle.

The lateral meniscus is smaller and more freely movable than the medial meniscus, but it covers a larger area of articular surface than does the medial meniscus.

The tendon of the popliteus muscle and bursa separate the lateral meniscus from the fibular collateral ligaments.

The anterior and posterior horns of the lateral meniscus are attached close together in the anterior and posterior intercondylar areas. A strong tendinous slip, called the posterior meniscofemoral ligament, joins the lateral meniscus to the posterior cruciate ligament and the medial femoral condyle.

Bursae around the Knee

Several bursae are present around the knee because most tendons around the knee joint run parallel to the bones and pull lengthwise across the joint.

Four bursae communicate with the synovial cavity of the knee joint; they lie deep to the tendons of the quadriceps femoris, the popliteus, and the medial head of the gastrocnemius muscle.

The Suprapatellar (Quadriceps) Bursa

This large saccular extension of the synovial capsule passes superiorly between the femur and the tendon of the quadriceps femoris muscle.

The clinically important suprapatellar bursa extends about 8 cm superior to the base of the patella.

The suprapatellar bursa permits free movement of the quadriceps tendon over the distal end of the femur and facilitates full extension and flexion of the knee joint.

The bursa is held in position by the part of the vastus intermedius muscle called the articular genus muscle.

Injuries involving the suprapatellar bursa

Because the suprapatellar bursa communicates freely with the synovial cavity of the knee joint, it is regarded as a part of it.

Stab or puncture wounds superior to the patella may infect the knee joint via the suprapatellar bursa. It may also be involved in fractures of the femur resulting in hemarthrosis of the knee joint (blood in the joint cavity).

The Popliteus Bursa

This extension of the synovial cavity lies between the tendon of the popliteus muscle and the lateral condyle of the tibia.

The bursa opens into the lateral part of the synovial cavity, inferior to the lateral meniscus.

Sometimes the bursa is also continuous with the synovial cavity of the proximal tibiofibular joint as a result of perforation of the partition between the popliteus bursa and its joint cavity.

The Anserine Bursa (Bursa anserina)

This complicated bursa has several diverticula and separates the tendons of the sartorius, gracilis and semitendinosus muscles from the proximal part of the medial surface of the tibia and from the tibial collateral ligament.

The Gastrocnemius Bursa

This extension of the synovial cavity of the knee joint lies deep to the proximal attachment of this the tendon of the medial head of the gastrocnemius muscle. As it separates the tendon from the femur, it is often called the subtendinous bursa of the gastrocnemius.

The Semimembranosus Bursa

This bursa is related to the distal attachment of the semimembranosus muscle related to the distal attachment of the semimembranosus muscle and is located between the medial head of the gastrocnemius and the semimembranosus tendon.

Frequently it is a prolongation of the gastrocnemius bursa and communicates with the knee joint cavity.

The Subcutaneous Prepatellar Bursa

This bursa lies between the skin and the anterior surface of the patella. It allows free movement of the skin over the patella during flexion and extension of the leg.

Because of its superficial and exposed position, this bursa may become inflamed after prolonged periods of weight bearing on the hands and knees.

Prepatellar bursitis This is a friction bursitis caused by friction between the skin and the patella. If the inflammation is chronic, the bursa becomes distended with fluid and forms a soft, fluctuant swelling anterior to the knee.

This condition is commonly called "housemaid's knee".

The Subcutaneous Infrapatellar Bursa This bursa is located between the skin and the tibial tuberosity.

It allows the skin to glide over the tibial tuberosity and withstand pressure when kneeling with the trunk upright (e.g., when one kneels or genuflects during praying).

Subcutaneous infrapatellar bursitis

This results from excessive friction between the skin and the tibial tuberosity. The swelling occurs over the proximal end of the tibia.

This condition has been called "clergyman's knee".

The Deep Infrapatellar Bursa

This small bursa is lies between the patellar ligament and the anterior surface of the tibia, superior to the tibial tuberosity.

It is separated from the knee joint by the infrapatellar fatpad, a mass of fatty tissue between the superior part of the patellar ligament and the synovial capsule.

Deep infrapatellar bursitis

It results in a swelling between the patellar ligament and the tibia, superior to the tibial tuberosity. The swelling is less pronounce than that associated with subcutaneous prepatellar bursitis.

Enlargement of this bursa obliterates the dimples one each side of the patellar ligament when the leg is extended. Obliteration of these dimples may also result from synovial effusion.

The knee joint capsule

The joint capsule is a thick ligamentous structure that surrounds the entire knee. Inside this capsule is a specialized membrane known as the synovial membrane which provides nourishment to all the surrounding structures. Other structures include the infrapatellar fat pad and bursa which function as cushions to exterior forces on the knee. The capsule itself is strengthened by the surrounding ligaments

Menisci (knee cartilage)

Each knee joint has two crescent-shaped cartilage menisci. These lie on the medial (inner) and lateral (outer) edges of the upper surface of the tibia bone. They are essential components, acting as shock absorbers for the knee as well as allowing for correct weight distribution between the tibia and the femur.

BONY STRUCTURES

A. Distal Femur 1. Lateral and Medial Condyles

a. Articulate with tibia

2. Intercondylar fossa

3. Patellar articular surface

B. Patella

1. Sesamoid bone found within the tendon of the quadriceps femoris

2. Articulates with the patellar surface of the femur

3. Protects quadriceps tendon as tendon moves across knee joint

C. Proximal End of Tibia

1. Lateral and Medial tibial condyles

a. Articulates with femoral condyles

2. Intercondylar eminence

3. Intercondylar area - anterior

a. Found anterior to the intercondylar eminence

b. Provides attachment for anterior cruciate ligament

2. Intercondylar area - posterior

a. Found posterior to the intercondylar eminence

b. Provides attachment for posterior cruciate ligament

2. Tibial tuberosity

a. Point of insertion od the ligament of the patella

B. D. Fibula - proximal end

1. Head of fibula articulates with the lateral tibial condyle

2. Not involved in weight bearing during standing

3. Provides attachments for muscles

ALIGNMENT OF THE KNEE

A. Normal Alignment (Fig. 1) 1. Slight valgus position

a. Angle between longitudinal axis of femur and tibia is 1700 opened laterally

b. Q angle ( Fig. 1) - is a measure of the axis of pull of the quadriceps tendon and that of the ligament of the patella. The former is measured by a line drawn from the ASIS to center of patella. The latter is determined by a line drawn from the tibial tuberosity to the center of the patella. The normal Q angle is between 15 -200. This angle is somewhat greater in females than males. A Q angle much greater than normal means the patella will track in a lateral direction rubbing against the lateral femoral condyle causing Patella pain.

B. Abnormal Alignment ( Fig. 3)

1. Genu Valgum ( Knock Knee)

a. Tibia abducted with respect to femur

b. Angle between longitudinal axes of bones less than 1700

2. Genu Varum (Bow Leg)

a. Tibia adducted with respect to femur

b. Angle between longitudinal axes of bones greater than 1700

CAPSULAR LIGAMENTS

A. Function 1. Strengthen the fibrous capsule

B. Strengthening Anterior Aspect of Knee Joint

1. Quadriceps Tendon

a. Passes over and partially attaches to patella

b. Continues to insert onto tibial tuberosity as the Patellar Ligament

2. Patellar Retinacula

a. Extensions of fascia from the quadriceps muscles

b. Attach patella and patellar ligament to tibial and femoral condyles

B. trengthening the Posterior Aspect of the Knee Joint

1. Oblique Popliteal Ligament

a. Derived from the tendon of the semimembranosus muscle

2. Arcuate Popliteal Ligament

a. Derived from the tendon of the biceps femoris muscle

B. Strengthening the Medial Aspect of the Knee Joint

1. Tibial ( Medial ) Collateral Ligament

2. Attaches from medial femoral condyle superiorly to the media tibial condyle inferiorly

3. Attaches to medial meniscus

4. Forms part of the capsule and strengthens capsule medially

C. Lateral Aspect of the Knee Joint

1. Fibular ( Lateral ) Collateral Ligament

a. Attaches from lateral femoral condyle superiorly to head of fibula inferiorly

b. Does not attach to lateral meniscus

c. Not part of the fibrous capsule

d. Does not strengthen the fibrous capsule

i. capsule weak laterally

INTRACAPSULAR LIGAMENTS

A. Anterior Cruciate 1. Arises from anterior intercondylar area to tibia

2. Attaches to medial surface of lateral femoral condyle

3. Resists anterior movement of tibia on femur or posterior movement of femur on tibia

4. Anterior Draw Sign

a. Integrity of anterior cruciate ligament

B. Posterior Cruciate

1. Arises from posterior intercondylar area to tibia

2. Attaches to lateral surface of medial femoral condyle

3. Resists posterior movement of tibia on femur or anterior movement of femur on tibia

C. Posterior Meniscofemoral Ligament

1. Continuation of lateral meniscus attaching to the posterior cruciate ligament

MENISCI

A. Properties 1. Composed of fibrocartilage

2. Cover the superior surface of the tibial condyles

3. Adapt the shapes of the tibial condyles to provide a better fit between tibial and femoral condyles

B. Lateral Meniscus

1. Covers the surface of the lateral tibial condyle

2. Oval shape

3. Thicker, shorter and more closed shaped than medial meniscus

4. Mobile

C. Medial Meniscus

1. Covers medial tibial condyle

2. C. shaped

3. Larger, thinner and more opened shaped than lateral meniscus

4. Less mobile

a. Provides attachment for medial collateral ligament

b. More likely to be injured when medial collateral ligament is damaged

c. Abduction injury

i. i) Caused by lateral blow to knee

ii. ii) Stresses medial collateral ligament

iii. iii) Can lead to damage of ligament and medial meniscus

B. Transverse Ligament of the KneeContinuation anteriorly of fibers from the lateral meniscus to the medial meniscus

C. Coronary Ligaments

1. Extensions of the fibrous capsule

2. Attach the menisci to the tibial condyles

LOCKING OF THE KNEE JOINT

A. Function 1. Permits standing upright with little expenditure of energy in the form of muscle contraction

B. Shape of the Femoral Condyles

1. Lateral Femoral Condyle

a. Flexion

1. Spherical posterior part of femoral condyle in contact with tibial condyle

2. Bones remain in contact throughout flexion

3. Distance between femoral and tibial condyles changes little during flexion

4. Fibular collateral ligament is lax

b. Extension

1. Flat anterior part is in contact with tibial condyle

2. Less contact between bones as extension continues

3. Distance between both bones increases as extension proceeds

4. Fibular collateral ligament becomes taut

2. Medial Femoral Condyle

a. Flexion

1. Spherical posterior part of femoral condyle in contact with tibial condyle

2. Bones remain in contact throughout flexion

3. Distance between femoral and tibial condyles changes little during flexion

4. Tibial collateral ligament is lax

b. Extension

1. Flat anterior part is in contact with tibial condyle

2. Less contact between bones as extension continues

3. Distance between both bones increases as extension proceeds

4. Tibial collateral ligament becomes taut

2. Length of the Femoral Condyles

a. Articular surface of the medial femoral condyle is longer than the surface on the lateral femoral condyle

b. Moving into extension from a flexed position

1. Articular surface of lateral femoral condyle stops

2. Surface for articulation still exposed on medial condyle

c. Medial Rotation accompanies final stages of extension

1. Accommodates remainder of exposed articular surface on medial femoral condyle

2. Promotes greater contact between articular surfaces of femoral and tibial condyles

3. Tightens collateral and cruciate ligaments

2. 4. Locked Position

a. Brought about by medial rotation of the femur on the tibia during final stages of extension

b. Promotes maximum contact between articular surfaces of femoral and tibial condyles

c. Renders ligaments taut

d. Ligaments maintain the joint in the stable ( extended) position

UNLOCKING OF THE KNEE JOINT

A. Properties 1. Lateral rotation of the femur on the tibia

2. Brought about by action of the Popliteus Muscle

a. Arises from lateral femoral condyle

b. Inserts into the posterior part of the tibia

c. Pulls the lateral condyle posteriorly laterally rotating the femur

2. Necessary to loosen the tension on the ligaments

a. Collateral ligaments

b. Cruciate ligaments

MOVEMENTS OF THE KNEE

A. Properties of the Knee Joint 1. Uniaxial modified hinge joint

2. Weight bearing (fixed) - foot in contact with ground and the limb is supporting weight of body

a. Femur moves on a fixed tibia

1. Deep knee bends

2. Non Weight bearing (free) - foot free of ground and the limb is unable to support weight of body

a. Tibia free to move on a fixed femur

B. Movements at the Knee

1. Flexion / Extension

a. Occurs in sagittal plane

b. Coronal ( side to side) axis through knee joint

B. Inward / Outward Rotation

1. Occurs only when the knee is flexed

2. b. Vertical axis through tibial shaft

C. Muscle ActionsThe movements that can occur at the knee joint and the muscles acting as prime movers for each motion are outlined in Chart 1

Knee Joint

The knee joint has the following normal ranges of movement: Flexion and Extension

CLINICAL CONSIDERATIONS

A. Actions of the Knee Joint During Gait (Review the video "The Anatomical Gait Cycle") 1. Acceleration and Heel Strike

The knee is in a flexed position when the heel comes in contact with the ground. Flexion enables the knee to help absorb impact resulting from heel contacting ground. In addition, the mass of body behind knee joint forcing it into flexed position

a. Quadriceps femoris contract eccentrically to restrict flexion b. Skiing position

2. Heel Strike to Midstance

The movement of the torso that results when the non reference limb swings forward carries the torso over the reference limb. The knee joint of the reference limb assumes an extended position. This lengthens the limb facilitating the ability of the limb to support the weight of the torso.

a. Concentric contraction of quadriceps femoris assists in knee extension 2. Midstance to Toe Off

The knee joint is flexed by the concentric contraction of the gastrocnemius muscle. This shortens the limb enabling it to clear the ground in order to swing forward during the following interval.

3. Toe Off to AccelerationThe reference limb goes from a weight bearing to a non weight bearing position. The gastrocnemius along with the soleus muscle contracts concentrically during this phase with the gastrocnemius causing the knee joint to actively flex.

B. The Effect of Nerve Lesions on the Hip Joint During Gait

1. Femoral nerve

a. Wasting of muscles in anterior compartment of thigh

b. Extending knee against resistance very difficult. The patient will not be able to rise from a seated position without the use of the upper limbs for support because the quadriceps muscles are not capable of the concent contraction necessary to put the knee in an extended position.

c. The quadriceps muscles will not be able to contract in an eccentric manner. Thus, the patient will not be able to sit from a standing position without using the upper limbs for support.

d. Patient will walk with an abnormal gait since the quadriceps muscles will not be able to contract in an eccentric manner during the interval between swing and heel strike. Without the ability to restrain the amount of knee flexion during this interval, normal gait is impossible. The patient compensates by taking very small steps and having the foot come down in midstance rather than heel strike.

2. L3,4 nerve root damage will effect result in weak action of the quadriceps femoris. To test for damage of these roots, have the patient sit and have them try and extend their knee against resistance. Patients with L3,4 damage will have very weak knee extension.

B. Ligament or Meniscal DamageThe muscles and ligaments stabilize the knee under usual conditions. However, many activities such as sports can damage the knee. Assessing the knee for ligament damage or cartilage tears is something most physicians should be able to do.

1. Anterior Cruciate Ligament - is very susceptible to tears becuase it is stressed whenever a forward movement is suddenly stopped such as occurs during tennis, basketball skiing, etc. To asses damage to this ligamnent, the patient is asked to lie supine and the knee is placed is a position of slight flexion. The femur is stabilized with 1 hand while the leg is pulled forward with the other. Anterior movement of the leg on the thigh is a positive anterior draw sign indicative of anterior cruciate damage.

2. Posterior Cruciate Ligament - is less often damaged. To test its integrity, the opposite is done. With a stabilized thigh, the leg is pulled posteriorly. To great a movement indicates damage to this ligament.

3. Medial Collateral Ligament - is more commonly injured that the lateral (fibula) collateral ligment because it resists valgus stresses. A valgus stress is one in which a force applied to the outside ( lateral) aspect of the knee joint. This forces the knee in a medial direction causing the the tibia and femur to separate on the medial side. The medial collateral ligament resists such a force.

a. To test for the integrity of the Medial Collateral Ligament, place the limb in an extended position. Place one hand on the medial side of the ankle and the other on the lateral side of the knee. Pull the ankle laterally (outward) with one hand while stabilizing the knee with the other. Laxity indicates medial collateral ligament damage.

2. Lateral Collateral Ligament - resists varus stresses A varus stress is one in which a force applied to the inside ( medial) aspect of the knee joint. This forces the knee in a lateral direction causing the the tibia and femur to separate on the lateral side. The lateral collateral ligament resists such a force.

a. To test for the integrity of the Lateral Collateral Ligament, place the limb in an extended position. Place one hand on the lateral side of the ankle and the other on the medial side of the knee. Pull the ankle medially (inward) with one hand while stabilizing the knee with the other. Laxity indicates medial collateral ligament damage.

2. Meniscus- The menisci are cartilagenous plates that help adapt the shape of the femur to the tibia and also act as shock absorbers. Continued pounding, as occurs with road running on playing on a hard surface ( basketball) can result in tears of the menisci. Damage to the medial collateral ligament can also result in injury to the medial meniscus because to the attachment of the medial collateral ligament to this meniscus. The lateral collateral ligament has no attachment to the lateral meniscus so it is very moveable and less like to be injured.

a. To test for the integfrity of the menisci, have the patient lie supine with the knee flexed. Push down on the knee with one hand. The other hand grasps the heel and rotates the leg in either a medial or lateral direction. Pain caused by rotating the knee in a medial direction indicates damage to the lateral meniscus. Eliciting pain from rotating the leg in a lateral direction indicates damage to the medial meniscus.

Chart 1 -PRIME MOVERS OF THE KNEE

MOVEMENT MUSCLES NERVE SEGMENT

Extension Rectus femoris* Femoral L 2, 3, 4

Vastus Medialis* Femoral L 2, 3, 4

Vastus Lateralis* Femoral L 2, 3, 4

Vastus Intermedius* Femoral L 2, 3, 4

Flexion Semimembranosus+ Sciatic L 5 S 1

Semitendinosus + Sciatic L 5 S 1

Biceps Femoris+ Sciatic L 5 S 1,2

Sartorius Femoral L 3, 4

Gracilis Obturator L 3, 4

Gastrocnemius Tibial S 1,2

Unlocking Popliteus Sciatic (T) L 4, 5 S 1

Outward Rotation1

Biceps Femoris Sciatic L 5 S 1,2

Inward Rotation1

Sartorius2 Femoral L 3, 4

Gracilis2 Obturator L 3, 4

Semitendinosus Sciatic L 5 S 1

* = Quadriceps Femoris Muscles

+ = Hamstring Muscles

1 = Inward and Outward rotation are possible only if the knee is in a flexed position

2 = Pes anserinous muscles

Figure 1 - Knee Alignment

1. Normal Alignment - Notic that the tibia (2) is abducted with respect to the femur (1) imparting a valgus position to the knee joint.

2.Q Angle - a line connecting the ASIS (A) with the center of the patella (B) indicates the pull of the quadriceps tendon. A line theough the center of the patella to the tibial tuberosity indicates the pull of the ligament of the patella. The distance between these lines equals the Q angle

Figure 2

1.Genu Valgum - A force is applied to the lateral side of the knee forcing the knee to bend in a medial direction. This abducts the tibia with respect to the femur.

2. Genu Varum - A force is applied to the medial side of the knee forcing the knee to bend in a lateral direction. This adducts the tibia with respect to the femur.

Objectives:

A. Know the bony , ligamentous and cartilaginous structures the comprise the knee joint 1. Understand the role each plays in supporting and strengthening the knee joint

B. Know the proper alignment of the knee

1. Be able to distinguish genu valgum from genu varus

2. Understand how these conditions might occur.

3. Understand the anatomical basis of the Q angle and how it could lead to joint pain

C. Understand the mechanisms involved with locking and unlocking of the knee

1. Know how the shape of the femoral condyles determines how the knee locks

2. Know the role of the popliteus muslce in unlocking the knee.

D. Know the attachments, actions, segmental and peripheral innervation of the muscles acting on the knee

1. Be able to asses the function(s) of these muscles during the normal range of motion of the knee

2. Be able to localize the site of appropriate nerve lesion by defecits in knee movement

3. Be able to differentiate between how peripheral nerve lesions effect the knee from that of a lesion of the roots of the lumbosacral plexus.

E. Understand the factors responsible for the position of the knee joint during each interval of the gait cycle.

1. Be able to determine the site of a nerve lesion by defecits produced at the knee joint during gait.

F. Understand the functions of thye ligaments and cartilages of the knee joint.

1. Be able to test for the integrity of the muscles,ligaments and cartilages of the knee.

Ligaments of the knee joint

1. medial collateral ligament (MCL) 2. lateral collateral ligament (LCL)

3. anterior cruciate ligament (ACL)

4. posterior cruciate ligament (PCL)

The stability of the knee owes greatly to the presence of its ligaments. Each has a particular function in helping to maintain optimal knee stability in a variety of different positions.

1. Medial Collateral Ligament (MCL) - This band runs between the inner surfaces of the femur and the tibia. It resists forces acting from the outer surface of the knee- valgus forces.

2. Lateral Collateral Ligament (LCL) - This ligament travels from the outer surface of the femur to the head of the fibula. It resists impacts from the inner surface of the knee- varus forces.

3. Anterior Cruciate Ligament (ACL) - The ACL is one of the most important structures in the knee- not least because injury to it may require extensive surgery and rehabilitation. The cruciate ligaments are so called because they form a cross in the middle of the knee joint. The ACL, travels from the anterior (front) of the tibia to the posterior (back) of the femur and prevents the tibia moving forward. It is most commonly injured in twisting movements.

4. Posterior Cruciate Ligament (PCL) - This ligament travels from the posterior surface of the tibia to the anterior surface of the femur and in doing so wraps around the ACL.

Ligaments are tough bands of tissue that connect the ends of bones together. Two important ligaments are found on either side of the knee joint. They are the medial collateral ligament (MCL) and the lateral collateral ligament (LCL).

Inside the knee joint, two other important ligaments stretch between the femur and the tibia: the anterior cruciate ligament (ACL) in front, and the posterior cruciate ligament (PCL) in back. The MCL and LCL prevent the knee from moving too far in the side-to-side direction. The ACL and PCL control the front-to-back motion of the knee joint.

The ACL keeps the tibia from sliding too far forward in relation to the femur. The PCL keeps the tibia from sliding too far backward in relation to the femur. Working together, the two cruciate ligaments control the back-and-forth motion of the knee. The ligaments, all taken together, are the most important structures controlling stability of the knee.

Two special types of ligaments called menisci sit between the femur and the tibia. These structures are sometimes referred to as the cartilage of the knee, but the menisci differ from the articular cartilage that covers the surface of the joint.

The two menisci of the knee are important for two reasons: (1) they work like a gasket to spread the force from the weight of the body over a larger area, and (2) they help the ligaments with stability of the knee.

Imagine the knee as a ball resting on a flat plate. The ball is the end of the thighbone as it enters the joint, and the plate is the top of the shinbone. The menisci actually wrap around the round end of the upper bone to fill the space between it and the flat shinbone. The menisci act like a gasket, helping to distribute the weight from the femur to the tibia.

Without the menisci, any weight on the femur will be concentrated to one point on the tibia. But with the menisci, weight is spread out across the tibial surface. Weight distribution by the menisci is important because it protects the articular cartilage on the ends of the bones from excessive forces. Without the menisci, the concentration of force into a small area on the articular cartilage can damage the surface, leading to degeneration over time.

In addition to protecting the articular cartilage, the menisci help the ligaments with stability of the knee. The menisci make the knee joint more stable by acting like a wedge set against the bottom of a car tire. The menisci are thicker around the outside, and this thickness helps keep the round femur from rolling on the flat tibia. The menisci convert the tibial surface into a shallow socket. A socket is more stable and more efficient at transmitting the weight from the upper body than a round ball on a flat plate. The menisci enhance the stability of the knee and protect the articular cartilage from excessive concentration of force.

Taken all together, the ligaments of the knee are the most important structures that stabilize the joint. Remember, ligaments connect bones to bones. Without strong, tight ligaments to connect the femur to the tibia, the knee joint would be too loose. Unlike other joints in the body, the knee joint lacks a stable bony configuration. The hip joint, for example, is a ball that sits inside a deep socket. The ankle joint has a shape similar to a mortise and tenon, a way of joining wood used by craftsmen for centuries.

Tendons are similar to ligaments, except that tendons attach muscles to bones. The largest tendon around the knee is the patellar tendon. This tendon connects the patella (kneecap) to the tibia. This tendon covers the patella and continues up the thigh.

There it is called the quadriceps tendon since it attaches to the quadriceps muscles in the front of the thigh. The hamstring muscles on the back of the leg also have tendons that attach in different places around the knee joint. These tendons are sometimes used as tendon grafts to replace torn ligaments in the knee.

Muscle Groups surrounding the knee joint

The two main muscle groups of the knee knee joint are the quadriceps and the hamstrings. Both play a vital role, both moving and stabilizing the knee joint.

Quadriceps - The quadriceps muscle group is made up of four different individual muscles which join together forming the quadriceps tendon. This thick tendon connects the muscle to the patella which in turn connects to the tibia via the patellar tendon. Contraction of the quadriceps, pull the patella upwards and leads to knee extension.

Hamstrings-The hamstrings function in flexing the knee joint as well as providing stability on either side of the joint line.

The extensor mechanism is the motor that drives the knee joint and allows us to walk. It sits in front of the knee joint and is made up of the patella, the patellar tendon, the quadriceps tendon, and the quadriceps muscles. The four quadriceps muscles in front of the thigh are the muscles that attach to the quadriceps tendon. When these muscles contract, they straighten the knee joint, such as when you get up from a squatting position.

The way in which the kneecap fits into the patellofemoral groove on the front of the femur and slides as the knee bends can affect the overall function of the knee. The patella works like a fulcrum, increasing the force exerted by the quadriceps muscles as the knee straightens. When the quadriceps muscles contract, the knee straightens.

The hamstring muscles are the muscles in the back of the knee and thigh. When these muscles contract, the knee bends.

NervesThe most important nerve around the knee is the popliteal nerve in the back of the knee. This large nerve travels to the lower leg and foot, supplying sensation and muscle control. The nerve splits just above the knee to form the tibial nerve and the peroneal nerve. The tibial nerve continues down the back of the leg while the peroneal nerve travels around the outside of the knee and down the front of the leg to the foot. Both of these nerves can be damaged by injuries around the knee.

Blood Vessels

The major blood vessels around the knee travel with the popliteal nerve down the back of the leg. The popliteal artery and popliteal vein are the largest blood supply to the leg and foot. If the popliteal artery is damaged beyond repair, it is very likely the leg will not be able to survive. The popliteal artery carries blood to the leg and foot. The popliteal vein carries blood back to the heart.

Summary

The knee has a somewhat unstable design. Yet it must support the body's full weight when standing, and much more than that during walking or running. So it's not surprising that knee problems are a fairly common complaint among people of all ages. Understanding the basic parts of the knee can help you better understand what happens when knee problems occur.

Biomechanihe knee is the largest synovial joint in the body. It is composed of 3 bones analthough 2 of the 3 joints share a common cavity.

The bones of the knee comprise the femur (thigh bone), tibia (shin bone), patella (kneecap), and to a lesser degree the fibula. The knee joint itself is made up of the tibio-femoral joint, which itself is comprised of a medial compartment and a lateral compartment. The true knee joint also includes the patello-femoral joint. Another important component of the knee joint complex, although not part of the true knee joint, is the superior tibio-fibula joint.

The literature concerning kinematic and kinetic studies on the knee joint is comprehensively reviewed in this article. Also reviewed are studies of etiology and operative treatment of injury, as well as chronic disease such as dislocation, arthritis, and ligamentous rupture. This paper formulates experimental study and mathematical model analysis of the tibio-femoral and patello-femoral joints, respectively. The sections on experimental study cover the following: the tibio-femoral joint including load bearing capacity, knee laxity, ligamentous strain, articular geometry, and multiaxial movement; the patello-femoral joint including forces and stresses and patellar tracking patterns. Further, three items, considered as future problems, are discussed briefly: individual variations in material properties of the soft tissue and biphasic cartilage-bone

structures, quantitative description of bone geometry, and quantitative determination of extreme tensions and distortions in connective tissues surrounding the knee.

A two-dimensional anatomically based mathematical model of the human knee joint was developed to understand its biomechanics in deep flexion. The model was used to determine the internal knee loads as it simulates isometric quadriceps and hamstring co-contractions at different flexion angles during deep squat. It was found that in order to achieve deep flexion, large muscle forces are required, resulting in large tibio-femoral contact forces. In deep flexion, the femoral contact point was located on the most proximal point of the posterior condyle, location which was not affected by the level of quad activation. Conversely, the location of the tibial contact point was highly affected by the level of quad activation. Both anterior and posterior fiber bundles of the posterior cruciate ligament were found to carry high loads when the knee is maximally flexed. These results point to the important role of the posterior cruciate ligament in this position, and suggest the necessity of retaining this ligament during total knee replacement (TKR) procedures that allows for maximum flexion angles. Furthermore, the present data provide an explanation why most TKR's do not allow deep flexion: while contact occurs on the most proximal points of the posterior condyles in normal knees, this portion of the condyles is not presently resurfaced when performing a TKR.

Introduction to ankle joint anatomy:

The ankle joint acts like a hinge. But it's much more than a simple hinge joint. The ankle is actually made up of several important structures. The unique design of the ankle makes it a very stable joint. This joint has to be stable in order to withstand 1.5 times your body weight when you walk and up to eight times your body weight when you run.

Normal ankle function is needed to walk with a smooth and nearly effortless gait. The muscles, tendons, and ligaments that support the ankle joint work together to propel the body. Conditions that disturb the normal way the ankle works can make it difficult to do your activities without pain or problems.

Important Structures

The important structures of the ankle can be divided into several categories. These include

bones and joints ligaments and tendons

muscles

nerves

blood vessels

Bones and Joints

The ankle joint is formed by the connection of three bones. The ankle bone is called the talus. The top of the talus fits inside a socket that is formed by the lower end of the tibia (shinbone) and the fibula (the small bone of the lower leg). The bottom of the talus sits on the heelbone, called the calcaneus.

The talus works like a inside the socket to allow your foot to move up (dorsiflexion) and down (plantarflexion).

Woodworkers and craftsmen are familiar with the design of the ankle joint. They use a similar construction, called a mortise and tenon, to create stable structures. They routinely use it to make strong and sturdy items, such as furniture and buildings.

Inside the joint, the bones are covered with a slick material called articular cartilage. Articular cartilage is the material that allows the bones to move smoothly against one another in the joints of the body.

The cartilage lining is about one-quarter of an inch thick in most joints that carry body weight, such as the ankle, hip, or knee. It is soft enough to allow for shock absorption but tough enough to last a lifetime, as long as it is not injured.

The ankle is made up of 4 distinct bones, the tibia, fibula, talus and calcaneus. The interaction between these bones allows for movement of the joint in certain planes. In turn, the ankle is made up of 3 separate joints:

Talocrural Joint: This is a hinge joint formed by the distal ends of the fibula and tibula that enclose the upper surface of the talus. It allows for both dorsiflexion (decreasing the angle between the foot and the shin) and plantarflexion (increasing the angle).

Inferior tibiofibular Joint: This is strong joint between the lower surfaces of the tibia and fibula. This is supported by the inferior tibiofibular ligament.

Subtalar Joint: This joint comprises of the articulating surfaces of the talus and the calcaneus. It provides shock absorption and the movements of inversion and eversion (inward and outward ankle movements respectively) occur here.

Ligaments of the ankle joint

The ligaments of the ankle joint are comprised mainly of the collateral ligaments, both medial (inner) and lateral (outer). These are extremely important in the stability of the ankle itself:

A. Lateral Collateral Ligament:

The lateral collateral ligament prevents excessive inversion. It is considerably weaker than the larger medial ligament and thus sprains to the lateral ligament are much more common. It is made up of 3 individual bands:

1. Anterior talofibular ligament (AFTL): passes from the fibula to the front of the talus bone. 2. Calcaneofibular ligament (CFL)- connects the calcaneus and the fibula

3. Posterior talofibular Ligament (PTFL)- passes from the back of the fibula to the rear surface of the calcaneus.

B. Medial Collateral Ligament:

The medial ligament also known as the deltoid ligament is considerably thicker than the lateral ligament and spreads out in a fan shape to cover the distal (bottom) end of the tibia and the inner surfaces of the talus, navicular, and calcaneus.

Ligaments are the soft tissues that attach bones to bones. Ligaments are very similar to tendons. The difference is that tendons attach muscles to bones. Both of these structures are made up of small fibers of a material called collagen. The collagen fibers are bundled together to form a rope-like structure. Ligaments and tendons come in many different sizes and like rope, are made up of many smaller fibers. Thickness of the ligament or tendon determines its strength.

Ligaments on both sides of the ankle joint help hold the bones together. Three ligaments make up the lateral ligament complex on the side of the ankle farthest from the other ankle. (Lateral means further away from the center of the body.) These include the anterior talofibular ligament (ATFL), the calcaneofibular ligament(CFL), and the posterior talofibular

ligament (PTFL). A thick ligament, called the deltoid ligament, supports the medial ankle (the side closest to your other ankle).

Ligaments also support the lower end of the leg where it forms a hinge for the ankle. This series of ligaments supports the ankle syndesmosis, the part of the ankle where the bottom end of the fibula meets the tibia. Three main ligaments support this area. The ligament crossing just above the front of the ankle and connecting the tibia to the fibula is called the anterior inferior tibiofibular ligament (AITFL). The posterior fibular ligaments attach across the back of the tibia and fibula. These ligaments include the posterior inferior tibiofibular ligament (PITFL) and the transverse ligament. The interosseous ligament lies between the tibia and fibula. (Interosseous means between bones.) The interosseus ligament is a long sheet of connective tissue that connects the entire length of the tibia and fibula, from the knee to the ankle.

The ligaments that surround the ankle joint help form part of the joint capsule. A joint capsule is a watertight sac that forms around all joints. It is made up of the ligaments around the joint and the soft tissues between the ligaments that fill in the gaps and form the sac.

The ankle joint is also supported by nearby tendons. The large Achilles tendon is the most important tendon for walking, running, and jumping. It attaches the calf muscles to the calcaneus (heelbone) and allows us to raise up on our toes. The posterior tibial tendon attaches one of the smaller muscles of the calf to the underside of the foot. This tendon helps support the arch and allows us to turn the foot inward. The anterior tibial tendon allows us to raise the foot. Two tendons run behind the outer bump of the ankle (the lateral malleolus). These two tendons, called the peroneals, help turn the foot down and out.

Muscles

Most of the motion of the ankle is caused by the stronger muscles in the lower leg whose tendons pass by the ankle and connect in the foot. Contraction of the muscles in the leg is the main way that we move our ankle when we walk, run, and jump.

The key ankle muscles have been discussed earlier in the section on ligaments and tendons. These muscles and their actions are also listed here.

The peroneals (peroneus longus and peroneus brevis) on the outside edge of the ankle and foot bend the ankle down and out.

The calf muscles (gastrocnemius and soleus) connect to the calcaneus by the Achilles tendon. When the calf muscles tighten, they bend the ankle down.

The posterior tibialis muscle supports the arch and helps turn the foot inward.

The anterior tibialis pulls the ankle upward.

Nerves

The nerve supply of the ankle is from nerves that pass by the ankle on their way into the foot. The tibial nerve runs behind the medial malleolus. Another nerve crosses in front of the ankle on its way to top of the foot. There is also a nerve that passes along the outer edge of the ankle.

The nerves on the front and outer edge of the ankle control the muscles in this area, and they give sensation to the top and outside edge of the foot.

Blood Vessels

The ankle gets blood from nearby arteries that pass by the ankle on their way to the foot. The dorsalis pedis runs in front of the ankle to the top of the foot. (You can feel your pulse where this artery runs in the middle of the top of the foot.) Another large artery, called the posterior tibial artery, runs behind the medial malleolus. It sends smaller blood vessels to the inside edge of the ankle joint. Other less important arteries entering the foot from other directions also supply blood to the ankle.

Ankle Joint

The ankle joint has the following normal ranges of movement: Plantar Flexion, Dorsi Flexion, Inversion and Eversion.

COMPARTMENTS OF THE LEG

A. Anterior crural compartment

1. Muscles

a. Tibialis anterior

b. Extensor hallucis longus

c. Extensor digitorum longus

d. Peroneus tertius

2. Nerve

a. Deep Fibular (peroneal)

b. Motor - muscles of anterior compartment

c. Sensory - skin between first 2 toes

2. Artery

1. Anterior tibial

i. Muscular

ii. Malleolar

iii. Dorsalis pedis

2. Function

B. Lateral Crural Compartment

1. Muscles

a. Fibularis (peroneus) longus

b. Fibularis (peroneus) brevis

2. Nerve

a. Superficial Fibular (peroneal)

b. Motor - to muscles in lateral compartment

c. Sensory - dorsum of foot

2. 3. Artery

a. None

2. 4. Function (See Charts I & II)

B. C. Posterior Crural Compartment

1. Muscles

a. Superficial Group

i. Triceps SuraeGastrocnemiusSoleus

ii. Plantaris

b. Deep Group

i. Popliteus

ii. Tibialis posterior

iii. Flexor digitorum longus

iv. Flexor Hallucis longus

22 2. Nerve

a. a. Tibial

i. i) Motor - to muscles in posterior compartment

ii. ii) Sensory - to posterior lateral aspect of leg, dorsal lateral aspect of the foot, and plantar surface of heel

2. 3. Artery

1. a. Posterior tibial

i. i) Muscular

ii. ii) Malleolar

iii. iii) Peroneal

2. b. Fibular (peroneal)

i. i) Muscular

ii. ii) Malleolar

iii. iii) Perforating

2. 4. Function (See Charts I & II)

B. Collateral Circulation

1. Cruciate Anastomosis

1. Collateral circulation to leg and foot following blockage of femoral or popliteal arteries

2. Deep Femoral

3. Descending branch of lateral femoral circumflex a.

4. Femoral

5. Descending genicular artery

6. Popliteal

7. 5 genicular branches

8. Anterior Tibial

9. Recurrent branches

2. Crural Anastomosis

1. Collateral routes to foot following blockage of anterior or posterior tibial arteries.

2. Anterior Tibial artery

3. Medial & Lateral malleolar branches

4. c. Dorsalis Pedis artery

5. (1) Medial & lateral tarsal branches

6. Posterior Tibial artery

7. Malleolar branches

8. Fibular (peroneal) artery

9. Perforating branch

3. Deep Plantar Arch of Foot

1. Deep branch of Lateral Plantar artery

2. b. Dorsalis Pedis artery

3. Deep plantar artery

ANKLE JOINT

Function - The ankle joint is a hinge type joint that participates in movement and is involved in lower limb stability. There are 2 types of motions that take place at the ankle joint : dorsiflexion and plantar flexion. Dorsiflexion involves bringing the dorsum of the foot towards to the anterior surface of the leg. Such movement is necessary in order to have the foot contact the ground heel first during heel strike and to allow the foot to clear the ground during the swing phase of gait. Plantar flexion occurs when the toes are in contact with the ground and the heel is raised off of the ground ( toe raises). This movement provides the propulsive force necessary to lifer the limb off of the ground and start it swinging forward during the toe off portion of gait. During midstance, when the lower limb supports the weight of the torso, the ankle is in its most stable configuration which is the dorsiflexed position.

A. Bones 1. Modified hinge joint between the following bones:

a. Trochlea of the talus

b. Lateral malleolus of fibula

c. Medial malleolus of tibia

B. Ligaments

1. Deltoid

a. Binds medial malleolus to tarsal bones

b. Components

i. Tibionavicular

ii. Tibiocalcaneal

iii. Tibiotalaranteriorposterior

2. Lateral

a. Binds lateral malleolus to tarsal bones

b. Components

i. Talofibularanteriorposterior

ii. Calcaneofubular

B. Movement (See Charts 1 and 2 )

1. Oblique axis for motion

a. a. Posterior lateral portion of lateral malleolus

b. b. Anterior medial portion of medial malleolus

2. Terminology

a. Flexion of forefoot occurs with extension of hind foot

b. Terms dorsiflexion / plantar flexion used referring to movements at the ankle joint

2. Dorsiflexion

a. a. Bring dorsal surface of foot to anterior surface of leg

b. Accomplished by muscles in anterior crural compartment

2. Plantar flexion

a. Brings plantar surface of foot away from leg pointing the toes towards ground

b. Accomplished by action of superficial muscles in posterior crural compartment

B. Joint Stability

1. Most Stable Configuration

a. a. Dorsiflexed position

2. Properties

a. Shape of Ankle Bones

i. i) Trochlea tali wider anteriorly than posteriorly

ii. ii) Socket narrow posteriorly

b. Function of Ligaments

i. i) Interosseous membrane and Tibiofibular ligaments binds malleoli to trochlea

b. Joint locked into stable configuration during dorsiflexion

B. Role of Ankle Joint in Maintaining the Upright (Erect) Position

1. Center of Gravity

a. Falls in front of ankle joint

b. Forces body to move forward at the ankle joint

c. Ankle is forced into dorsiflexed position

d. Ankle locked in stable ( dorsiflexed ) position

2. Support of Ankle Joint

a. Lack of ligamentous support anteriorly or posteriorly

2. Muscle Activity

a. Needed to maintain the ankle joint in neutral position

b. Action of Triceps surae counterbalances force of gravity

i. Gravity forces body forward dorsiflexing ankle joint

ii. Ankle joint stable in dorsiflexed position

iii. Triceps surae muscles plantar flex ankle joint

iv. Restrict amount of dorsiflexion at ankle joint during normal standing

B. Injuries of the Ankle Joint

1. Sprains

a. Damage to ligamentous structures

b. More common on lateral side of ankle

i. Deltoid ( medial ) ligament strong

ii. Lateral ligaments weak

2. Inversion Injuries

a. Stress lateral side of ankle

b. Result of excessive foot inversion

c. Sprain lateral ligaments of ankle

2. Eversion Injuries

a. Stress medial side of ankle

b. Result of excessive foot eversion

c. Results in fracture dislocations

THE FOOT

Function - The foot plays an important role in supporting the weight of the entire body and in locomotion. The bones of the foot are arched longitudinally to help facilitate the support function The transverse arch helps with movements of the foot . These movements help keep the sole (plantar surface) in contact with the ground despite the unevenness of the ground surface. They also work in concert with the ankle joint to help propel the foot off the ground during toe off portion of gait. It is convenient to speak of 3 segments of the foot: hindfoot , midfoot and forefoot. The calcaneus and talus comprise the hindfoot while the metatarsals and phalanges make up the forefoot. The navicular, cuboid and cuneiform bones make up the midfoot.

A. Bones of the Foot 1. Tarsal Bones

a. Calcaneus

b. Talus

c. Navicular

d. Cuboid

e. Cuneiforms - Medial , intermediate, lateral

2. Metatarsals (5)

3. Phalanges

B. Arches of the Foot

1. Medial Longitudinal Arch

a. Calcaneus , Talus , Navicular , Cuneiform (3), Metatarsals - 1,2,3

b. Weight bearing

i. Pronounced curve

ii. Weight transferCalcaneus, metatarsal heads

2. Lateral Longitudinal Arch

a. Tuber calcaneus , Cuboid, Metatarsals 4 & 5

b. Weight bearing

i. Slight curve

b. Weight transfer

i. To ground

2. Transverse Arch

a. Cuneiform (3) , Cuboid, Base of metatarsals 1-5

b. Concave arch

B. Tarsal Joints - or intertarsal joints , are a complex of joints between the tarsal bones . These joints enable the forefoot to move in concert with the hind and midfoot . Movements at these joints are responsible for most of the important movements of the foot. The tarsal joints are synovial joints . These joints permit gliding and/or rotation movements.

1. Subtalar joint - the talus articulates with the calcaneus at 3 different sites. A fairly large concavity the tarsal sinus separates these articulations into anterior and posterior portions. The posterior portion is called the subtalar joint. Within the sinus , a strong ligament, the talocalcaneal interosseous ligament is found. This ligament helps keep the 2 bones applied to each other during movements of the subtalar joint. Inversion and eversion of the heel occurs mainly at the subtalar joint.

2. Transverse Tarsal Joints - are a combination of 3 separate joint spaces that include:

a. Talocalcanealnavicular joint - consists of the anterior articulation between the talus and calcaneus and the Talonavicular articulation

b. Calcanealcuboid joint

c. TalonavicularThough they consist of separate joints, each with their own articular surfaces and separate joint capsules, we will consider the transverse tarsal joints as a single unit. Movements of the transverse tarsal joints enable the forefoot to move on the midfoot.

B. Movements at the Tarsal Joints (See Chart III - Prime Movers of the Ankle and Tarsal Joints)

1. The movements that take place at the tarsal joints can be confusing to understand. Movements of the joints are complex, almost as complex and confusing as the terminology used to describe them. To simplify matters, the following terminology will be used:

a. The Neutral Position of the hindfoot occurs when the heel is aligned with the vertical axis of the tibia. That of the forefoot occurs when the base of the second metatarsal is aligned with the vertical axis of the tibia.

b. Heel Inversion - refers to the movement at the subtalar joint. Heel inversion occurs when the heel ( calcaneus) deviates medially ( inward) from the vertical axis of the tibia. (Fig. 1)

c. Forefoot Inversion occurs at the transverse tarsal joints. Forefoot inversion occurs when the second metatarsal deviates medially ( inward) from the vertical axis of the tibia. This movement also involves adduction of the forefoot.

d. Heel Eversion - refers to the movement at the subtalar joint. Heel eversion occurs when the heel ( calcaneus) deviates laterally ( outward) from the vertical axis of the tibia. (Fig. 2)

e. Forefoot Eversion occurs at the transverse tarsal joints. Forefoot eversion occurs when the second metatarsal deviates laterally ( outward) from the vertical axis of the tibia. This movement also involves abduction of the forefoot.

2. Supination/Pronation occur primarily at the transverse tarsal joints and involve movements of the forefoot..

a. Supination is a combination forefoot inversion and adduction occurring at the transverse tarsal joints. Supination occurs when the 1st metatarsal bone is elevated off the ground while the 5th metatarsal bone is depressed

b. Pronation is a combination of forefoot inversion and abduction. Now, the 5th metatarsal is elevated while the 1st. metatarsal is depressed

B. Plantar Ligaments

1. Function of Plantar Ligaments

a. Support tarsal joints

b. Support bony arches

i. "Fallen Arches"Loss of ligamentous support for bony arches

2. Plantar calcaneonavicular ( Spring) ligament

a. aBinds calcaneus to navicular bone

b. Supports talocalcaneonavicular joint

c. Main support for medial longitudinal arch

i. Flattens when weight is placed on arch

ii. Springs back when weight is removed returning arch to original shape

b. Weakness leads to fallen arches

2. 3. Plantar calcaneocuboid ( Short plantar) ligament

a. Binds calcaneus to cuboid bone

b. Supports lateral longitudinal arch

2. Long Plantar ligament

a. Binds calcaneus to cuboid bone and base of metatarsal

b. Supports lateral longitudinal arch

B. Alignment of the Foot

1. Pes Planus (Flat foot)

a. Weak plantar ligaments

b. Paralysis of peroneus longus

2. Pes Cavus ( Exaggerated Arch)

a. overactive peroneus longus

2. Pes Varus

a. Foot inverted and adducted

2. Pes Valgus

a. Foot everted and abducted

VASCULAR SUPPLY and INNERVATION OF THE FOOT

Dorsum

1. Arterial Supply

a. Dorsalis Pedis - is the continuation of the anterior tibial artery distal to the ankle joint

b. Lateral tarsal br.

c. Arcuate

d. 1st. dorsal metatarsal artery

e. Deep plantar

2. Veins

a. Dorsal venous arch

b. Short saphenous vein

c. Great saphenous vein

d. Dorsalis pedis vein

2. Innervation

a. Deep Fibular Nerve

i. Cutaneous to web space between 1st & 2nd toes

b. Superficial Fibular Nerve

i. Cutaneous to remainder of dorsum of foot

B. Plantar Surface

1. Posterior Tibial artery terminates as the medial and lateral plantar arteries

a. Supply muscles and skin of plantar surface of foot

b. Lateral plantar a. anastomoses with deep plantar branch of the dorsalis pedis to form deep plantar arch

2. Tibial nerve terminates as medial and lateral plantar nerves

a. Supply muscles and skin of plantar surface of foot

CLINICAL CONSIDERATIONS

A. Actions of the Ankle and Tarsal Joints During Gait (Review the video "The Anatomical Gait Cycle") 1. Acceleration and Heel Strike

The ankle joint is in a neutral position to enable the heel portion of the foot to contact the ground prior to any other portion of the foot. the ground.

a. Eccentric contractions of the muscles in the anterior crural compartment overcome the attempts of gravity to pull the ankle into a plantar flexed position.

2. Heel Strike to MidstanceThe torso moves forward passively on the reference side as the limb on the opposite side of the body is in transition between toe off and acceleration. As a result , the reference ankle assumes a dorsiflexed position.

a. Triceps surae muscles contract eccentrically to restrain the amount of passive dorsiflexion and also inverting the heel at the subtalar jointAs the foot progresses from heel strike to midstance, inversion of the heel and supination of the forefoot places much of the body's weight on the lateral longitudinal arch of the foot. Supination of the forefoot "locks" the transverse tarsal joints aiding in this weight bearing function.

2. Midstance to Toe OffThe reference limb is preparing to leave the ground. This is the stage where concentric contractions of the gastrocnemius and soleus muscles begin to plantar flex the ankle joint and the heel is being readied to raise off of the ground. The foot undergoes a number of changes during this phase.

a. Progression from midstance, the heel is everted at the subtalar joint and the forefoot pronated allowing the foot to be "loaded" as the weight of the body is transferred to the heads of the first 2 metatarsal bones.

b. As the gastrocnemius and soleus become more active and the heel begins to come off the ground, the heel is inverted and the forefoot is supinated . The tarsal joints "lock" and the foot is turned into a rigid lever supporting the ability of the limb to transition from stance to swing phase.

2. Toe Off to AccelerationThe reference limb goes from a weight bearing to a non weight bearing position. The gastrocnemius and

soleus muscles contract concentrically propelling the limb off of the ground as the reference limb enters the swing phase of gait.

a. Ankle is actively plantar flexed .

B. The Effect of Nerve Lesions on the Ankle and Tarsal Joints During Gait

1. Common Fibular (Peroneal) Nerve

a. Easily damaged as nerve winds superficially around the neck of the fibula.

b. Drop foot / Foot slap

c. Anterior crural muscles unable to contract eccentrically during interval between Acceleration and Heel Strike

d. Fore foot rather than the heel strikes the ground during Heel Strike

e. Patient produces a obvious "slapping" sound when going into Heel Strike

2. Tibial nerve

a. Inability to plantar flex ankle during interval between Toe Off and Swing

b. Patient will not be able to do toe raises

2. Segmental InnervationMovements at the ankle and tarsal joints provide means to determine which segments (roots) of the Lumbosacral may be damaged.

a. L 4

1. Inversion of subtalar joint

b. L 5

1. Dorsiflexion of ankle

c. S1

1. Plantar flexion of ankle

2. Eversion of subtalar joint

CHART I MUSCLES OF THE LEG

MUSCLE JOINT(S) ACTION(S) NERVE SEGMENT

Anterior Compartment:

Tibialis Anterior Ankle Transverse Tarsal

Dorsiflex Supinate

Deep Fibular (Peroneal)

L 4, 5 S 1

Extensor Hallucis Longus

Ankle Dorsiflex Deep Fibular (Peroneal)

L 4, 5 S 1

Extensor Digitorum Longus

Ankle Dorsiflex Deep Fibular (Peroneal)

L 4, 5 S 1

Fibularis Tertius Ankle Transverse

Dorsiflex Pronation

Deep Fibular (Peroneal)

L 4, 5 S 1

Tarsal

Lateral Compartment:

Fibularis (peroneus) Longus

Subtalar Transverse Tarsal

Eversion Pronation

Superficial Fibular (Peroneal)

L 4, 5 S 1

Fibularis (peroneus) Brevis

Subtalar Transverse Tarsal

Eversion Pronation

Superficial Fibular (Peroneal)

L 4, 5 S 1

Posterior Compartment:

Popliteus Knee Unlocks Tibial L 4, 5 S 1

Gastrocnemius Knee

Ankle

Subtalar

Flexion

Plantar flexion

Inversion

Tibial S 1,2

Soleus Ankle Subtalar

Plantar flexion Inversion

Tibial S 1,2

Plantaris Ankle Plantar flexion Tibial L5,S1

Tibialis Posterior Transverse Tarsal

Supination Tibial L 4, 5 S 1

Flexor Digitorum* Longus

Ankle Transverse Tarsal

Plantar flexion Inversion

Tibial L 4, 5

Flexor Hallucis* Longus Ankle Plantar f lexicon

Tibial L 4, 5

* Weak ankle plantar flexors. Act mainly on the toes

CHART II PRIME MOVERS OF THE ANKLE & TARSAL JOINTSMOVEMENT JOINT MUSCLES NERVE SEGMENT

Dorsiflexion Ankle Tibialis Anterior Deep Fibular (Peroneal)

L 4, 5 S 1

Extensor Hallucis Longus

Deep Fibular (Peroneal)

L 4, 5 S 1

Extensor Digitorum Longus

Deep Fibular (Peroneal)

L 4, 5 S 1

Fibularis Tertius Deep Fibular (Peroneal)

L 4, 5 S 1

Plantar flexion Ankle Gastrocnemius Tibial S 1, 2

Soleus Tibial S 1, 2

Plantaris Tibial L5,S 1, 2

Inversion Subtalar Tibialis Anterior Deep Fibular (Peroneal)

L 4, 5 S 1

Tibialis Posterior Tibial L 4, 5 S 1

Eversion Subtalar Fibularis (peroneus) Superficial Fibular L 4, 5 S 1

Longus (Peroneal)

Fibularis (peroneus) Brevis

Superficial Fibular (Peroneal)

L 4, 5 S 1

Pronation Transverse Tarsal

Fibularis (peroneus) Longus

Superficial Fibular (Peroneal)

L 4, 5 S 1

Supination Transverse Tarsal

Tibialis Anterior Deep Fibular (Peroneal)

L 4, 5 S 1

Tibialis Posterior Tibial L 4, 5 S 1

BASIC FOOT AND ANKLE BIOMECHANICS

Biomechanics is the term used to describe movement of the body. This section is a review of basic foot and ankle biomechanics. In order to understand the biomechanics of the foot and ankle it is important to understand their anatomy. Please read the sections on basic foot anatomy and basic ankle anatomy before reading this section.

The ankle is a modified hinge joint. It plays a key role in transferring the forces from the foot to the leg. The ankle joint is made up of three bones, which are connected by ligaments, muscles and tendons. A strong ligament joins the ends of the tibia and fibula to form the ankle "mortis". The "dome" of the talus (the highest bone of the foot) fits inside the ankle mortis to form the ankle joint. The ankle allows movement in only one plane. It allows the foot to move upwards (dorsiflexion) and downwards (plantar flexion).

The foot is made up of 26 bones. There are numerous joints between these bones that allow the foot to be both a rigid lever and a shock absorber. The largest joint in the foot is the subtalar joint. Inward movement of the foot (inversion), and outward movement of the foot (eversion) occur primarily at the subtalar joint.

The normal end ranges of motion for the foot and ankle vary between individuals and between children and adults. The following are approximate end ranges of motion for adults:

• Dorsiflexion - 20 degrees• Plantar flexion - 60 degrees• Eversion - 15 degrees• Inversion - 35 degrees

The gait cycle (walk cycle) describes what happens to the foot and ankle from the point of initial contact of one foot with the ground to the point at which the same foot contacts the ground again. The gait cycle is divided into the swing phase and the stance phase. During the swing phase the foot is not in contact with the ground. As the name implies it is the phase of the gait cycle in which the foot swings forward to take another step. During the stance phase the foot is in contact with the ground. The stance phase of the gait cycle can also be divided into three stages. The first stage is called heel strike, the second stage is called mid-stance, and heel lift is the final stage. The biomechanics of the foot are best explained by describing what happens to the foot during the stance phase of the gait cycle.

During heel strike of the stance phase the foot begins to pronate. Pronation of the foot is the term that describes the rolling motion of the foot inwards and flattening of the inner (medial) arch of the foot. Pronation allows the foot to adapt to uneven terrain and absorb the impact of the foot striking the ground. It is during this phase that the foot begins to act like a shock absorber

CONCLUSION

CONCLUSION:

For the conclusion, sports biomechanics is used to improve performance by developing techniques and to improvise the latest techniques to minimize injuries, maximize performance, develop exercise mode and lastly modify sports techniques. So, for the long jump, triple jump and high jump, the biomechanical principle will be able to minimize injuries and improvise performance.

In conclusion thinking Biomechanics means moving freely and preventing injury, Muscle balance, flexibility of muscles and free movement of nerve structures leads to Light Moves.

BIBLIOGRAPHY

BIBLIOGRAPHY

Internet sources

www.sportsinguryclinic.com

www.familydoctor.org.com

www.bodybuilding.com

www.adam.about.com

www.drprempillay.com

www.enginumich.edu

www.enjuriupdate.com

www.linkinghub.elserier.com

www.answers.com

www.apta.com

www.healthcare.com

www.medicallibray.com

www.fpnotebook.com