THE KNEE

Notes for Sports Medicine

The Knee• One of the most complex joints

• Extreme stress placed on the knee

• One of the most traumatized joints

• Hinge Joint (Not a true hinge)

• Stability depends primarily on the ligaments, joint capsule and muscles

• Provides stability during weight bearing and movement

• Unstable laterally and medially

Anatomy of the KNEE

• BONES– Femur

–Patella

– Tibia

– Fibula

Articulations

• Femur – Tibia

• Femur – Patella

• Femur – Fibula

• Tibia – Fibula

Boney Landmarks

• FEMUR

– Femoral Condyles

(Medial and Lateral Condyles)

– Femoral Notch

– Femoral Groove

• PATELLA

– Superior Pole

– Inferior Pole

– Medial Border

– Lateral Border

• TIBIA

– Tibial Plateau

– Tibial Tuberosity

– Popliteal Notch

– Tibial Spine

– Lateral Tibial Tubercle (Gerdy’s Tubercle)

• FIBULA

– Fibular Head

Anatomy of the Knee Cont.

• Muscles– Quads

• Rectus Femoris

• Vastus Lateralis

• Vastus Intermedius

• Vastus Medialis

– Hamstrings

• Biceps Femoris

• Semitendinosis

• Semimembranosis

Quads

Hamstrings

Anatomy of the Knee Cont.

• Ligaments– Medial Collateral

(MCL)

– Lateral Collateral (LCL)

– Anterior Cruciate (ACL)

– Posterior Cruciate (PCL)

Anatomy of the Knee Cont.

• Cartilage– Medial Meniscus (C)

– Lateral Meniscus (O)

– Medial Femoral Articular Cart.

– Lateral Femoral Articular Cart.

Anatomy of the Knee Cont.

• Other

• Plica – synovial folds that exist from fetal life.

• Bursae – Fluid filled sac to reduce friction– Infrapatellar

– Suprapatellar

• Arteries– Femoral

– Popliteal

Menisci

• Two oval (semilunar) fibrocartilages that deepen the articular facets of the tibia

• Cushion stress placed on the knee joint.

• Help stabilize the knee, especially the medial meniscus when flexed at 90.

Medial Meniscus

• C shaped cartilage

• Attached to the medial articular facet of the tibia and to the joint capsule

• Posteriorly attached to fibers of the semimembranosis

Lateral Meniscus

• More O shaped

• Attached to the lateral articular facet on the superior aspect of the tibia

• Attaches loosely to the lateral capsule and the popliteal tendon.

Other Meniscus Info

• Transverse ligament joins the anterior portions of the lateral and medial menisci

• Blood is supplied to each meniscus.

• Can be divided into three zones

– Red-Red zone (outer third) (best supply)

– Red-White zone (middle third) (minimal supply)

– White-White zone (inner third) (Avascular)

Stabilizing Ligaments

• The Cruciate Ligaments

– Accounts for a considerable amount of stability

– Cross one another with the joint cavity

– Highly vascularized

Anterior Cruciate (ACL)• Attaches below and in front of the tibia

• Passes backwards, attached to the inner surface of the lateral condyle.

• Comprises of three twisted bands

• Prevents femur from moving posterior during weight bearing

• Stabilizes against excessive internal rotation of the tibia.

• Secondary restraint for valgus and varus stress with collateral damage.

Anterior Cruciate

Posterior Cruciate (PCL)

• Stronger of the two

• Primary stabilizer of the knee

• Crosses from the back of the tibia in an upward, forward and medial direction

• Attaches to the anterior portion of the lateral surface of the medial condyle.

• Prevents Hyperextension

Posterior Cruciate

Capsular and Collateral Ligs.

• Additional stabilization of the knee is provided by the capsule and the collateral ligaments.

• Direct movement in a correct path.

Medial Collateral (MCL)

• 2 parts (Deep & Superficial)

• Attaches above the joint line on the medial epicondyle

• Attaches on the tibia, just below the pes anserinus muscle.

• Deep portion (posterior aspect) blends in with the capsule and the semimembranosis.

• Capsule attaches to the medial meniscus

MCL Cont.

• Fibers of the MCL are tight through flexion and extension.

• Prevent valgus (lateral) and external rotating forces.

Lateral Collateral (LCL)

• Round, fibrous cord shaped like a pencil

• Attaches on the lateral epicondyle and

• Attaches on the fibular head

• Taut during ext, but relaxed during flexion

• Prevents Varus (medial) force

Anterior Lateral (ALL) (new)?

• To more clearly define this possible ligament, the research team carefully dissected the knees of 41 cadavers ranging from 61-93 years old at death, roughly half men and half women. In all but one of the cadavers, there was clearly a small lateral ligament distinct from the other known structures around it, including the LCL. It is more clearly seen if the knee is partially bent (~60º angle) and the lower leg twisted inward slightly. This puts some stress on the ligament to make it stand out more. Because of the placement of the ligament, the authors have termed it the anterolateral ligament (ALL).

More -- ALL

• Based on the location of the ALL and some evidence from bone fracture patterns in some types of knee injuries, Claes and colleagues propose that the ALL has a role in stabilizing the knee during internal rotation

ALL & LCL

LCL & ALL

Other structures

• Deep Medial Capsular Ligaments

– Three parts, anterior, medial and posterior

– Purpose: attach the medial meniscus to the femur and to allow the tibia to move on the meniscus inferiorly

• Iliotibial Band (IT band)

– Attaches lateral epicondyle & Gerdy’s tubercle

• Popliteus – Stabilizes during flexion

• Biceps Femoris – attach fib head & capsule

Joint Capsule

• Largest joint capsule in the body

• Forms suprapatellar pouch

• Contains infrapatellar fat pad and bursae

• Medially a thickened section for the deep part of the MCL

• Posteriorly, forms two pouches that cover the condyles and tibial plateau

• Synovial Membrane line inner surface

Knee Muscles

• Knee Flexion

– Biceps femoris

– Semitendinosus

– Semimembranosus

– Gracilis

– Sartorius

– Gastrocnemius

– Popliteus

– Plantaris Muscles

• Knee Extension

– Vastus Medialis

– Vastus Lateralis

– Vastus Intermedius

– Rectus Femoris

Knee Muscles Cont.

• External Rotation

– Biceps Femoris

– Vastus Medialis

– Boney anatomy also produces external tibial rotation as the knee moves into extension.• Screwhome Mechanism

• Stability (lock out knees)

• Internal Rotation

– Popliteal

– Semitendinous

– Semimembranous

– Sartorius

– Gracilis

– Rotation is limited and can occur only when the knee is in a flexed position

Bursa

• Bursa is a flattened sac or enclosed cleft composed of synovial tissue

• Function is to reduce the friction

• Found between muscle and bone, tendon and bone, tendon and ligament …

• Suprapatellar, prepatellar, infrapatellar, pretibial, gastrocnemius

Fat Pads

• Infrapatellar is the largest

• Serves as a cushion to the front of the knee

• Separates the patellar tendon from the joint capsule

Nerve Supply

• Tibial Nerve– Hamstrings

– gastrocnemius

• Common Peroneal Nerve– Short head of the biceps

– Wraps around fibular head

• Femoral– Quads

– Sartorius

Blood Supply

• Femoral Artery

– Popliteal Artery

• Medial and Lateral Superior Genicular

• Middle Genicular

• Medial and Lateral Inferior Genicular

Functional Anatomy

• Flexion (140 degrees)

• Extension (0 - -5 degrees)

• Rotation

• Rolling

• Gliding

• Axial Rotation (Screw Home Mechanism)– External Rotation – locks knee in spot

– Last 15 degrees of extension (VMO)