APPLIED ANATOMY OF KNEE

-Dr Anurag

Ranga

THE KNEE JOINT COMPLEX CONSISTS OF THE FEMUR, THE TIBIA, THE FIBULA, AND THE PATELLA

ArticulationsThe knee joint complex consists of three articulations between

femur and the tibia,

femur and the patella,

tibia and the fibula.

Characterized by two large condyles, which articulate withthe proximal head of the tibia.

The condyles are separated posteriorly by anintercondylar fossa and are joined anteriorly where theyarticulate with the patella.

The surfaces of the condyles that articulate with the tibiaare rounded posteriorly and become flatter inferiorly.

The walls of the intercondylar fossa bear two facets for thesuperior attachment of the cruciate ligaments, whichstabilize the knee joint.

The wall formed by the lateral surface of the medialcondyle has a large oval facet, which covers most of theinferior half of the wall, for attachment of the proximal endof the posterior cruciate ligament;

The distal end of femur

The wall formed by the medial surface of the lateralcondyle has a posterosuperior smaller oval facet forattachment of the proximal end of the anteriorcruciate ligament

Epicondyles, for the attachment of collateralligaments of the knee joint, are bony elevations onthe nonarticular outer surfaces of the condyles.

Two facets separated by a groove are just posteriorto the lateral epicondyle: the upper facet is forattachment of the lateral head of the gastrocnemiusmuscle; the inferior facet is for attachment of thepopliteus muscle.

The medial epicondyle is a rounded eminence onthe medial surface of the medial condyle. Justposterosuperior to the medial epicondyle is theadductor tubercle.

PR0XIMAL END OF TIBIA

The proximal end of the tibia is expanded in thetransverse plane for weight bearing and consists of amedial condyle and a lateral condyle, which are bothflattened in the horizontal plane and overhang the shaft.

The superior surfaces of the medial and lateral condylesare articular and separated by an intercondylar region,which contains sites of attachment for strong ligaments(cruciate ligaments) and interarticular cartilages (menisci)of the knee joint.

The articular surfaces of the medial and lateralcondyles and the intercondylar region together forma "tibial plateau," which articulates with and isanchored to the distal end of the femur. Inferior tothe condyles on the proximal part of the shaft is alarge tibial tuberosity and roughenings for muscleand ligament attachments.

The medial condyle is larger than the lateral condyleand is better supported over the shaft of the tibia. Itssuperior surface is oval for articulation with themedial condyle of the femur. The articular surfaceextends laterally onto the side of the raised medialintercondylar tubercle

The superior surface of the lateral condyle is circularand articulates above with the lateral condyle of thefemur.

The medial edge of this surface extends onto theside of the lateral intercondylar tubercle

The superior articular surfaces of both the lateraland medial condyles are concave particularlycentrally. The outer margins of the surfaces areflatter and are the regions in contact with theinterarticular discs (menisci) of fibrocartilage inthe knee joint.

The intercondylar region of the tibial plateau liesbetween the articular surfaces of the medial andlateral condyles. It is narrow centrally where it israised to form the intercondylar eminence, thesides of which are elevated further to formmedial and lateral intercondylar tubercles.

The intercondylar region bears six distinct facets forthe attachment of menisci and cruciate ligaments.

The anterior intercondylar area widens anteriorlyand bears three facets:

the most anterior facet is for attachment of theanterior end (horn) of the medial meniscus;

immediately posterior to the most anterior facet isa facet for the attachment of the anterior cruciateligament;

a small facet for the attachment of the anterior end(horn) of the lateral meniscus is just lateral to thesite of attachment of the anterior cruciate ligament.

The posterior intercondylar area also bears threeattachment facets: the most anterior is forattachment of the posterior horn of the lateralmeniscus; posteromedial to the most anterior facetis the site of attachment for the posterior horn of themedial meniscus; behind the site of attachment forthe posterior horn of the medial meniscus is a largefacet for the attachment of the posterior cruciateligament.

PROXIMAL END OF FIBULA

The fibula is the lateral bone of the leg and does nottake part in formation of the knee joint or inweightbearing. It is much smaller than the tibia andhas a small proximal head, a narrow neck, and adelicate shaft, which ends as the lateral malleolus atthe ankle.

The head of the fibula is a globe-shaped expansion atthe proximal end of the fibula. A circular facet on thesuperomedial surface is for articulation above with asimilar facet on the inferior aspect of the lateralcondyle of the tibia. Just posterolateral to this facet,the bone projects superiorly as a blunt apex (styloidprocess).

PATELLA

The patella (knee cap) is the largest sesamoid bone (abone formed within the tendon of a muscle) in the body andis formed within the tendon of the quadriceps femorismuscle as it crosses anterior to the knee joint to insert onthe tibia.

The patella is triangular.

Its apex is pointed inferiorly for attachment to the patellarligament, which connects the patella to the tibia

Its base is broad and thick for the attachment of thequadriceps femoris muscle from above;

Its posterior surface articulates with the femur and hasmedial and lateral facets, which slope away from a raisedsmooth ridge-the lateral facet is larger than the medial facetfor articulation with the larger corresponding surface on thelateral condyle of the femur.

The following is a list of knee actions and the muscles that

initiate them.

•Knee flexion is executed by the biceps femoris,

semitendinosus, semimembranosus, gracilis, sartorius,

gastrocnemius, popliteus, and plantaris muscles.

• Knee extension is executed by the quadriceps muscle of

the thigh, consisting of three vasti—the vastus medialis,

vastus lateralis, and vastus intermedius—and by the rectus

femoris.

External rotation of the tibia is controlled by the biceps

femoris. The bony anatomy also produces external tibial

rotation as the knee moves into extension.

Internal rotation is accomplished by the popliteal,

semitendinosus, semimembranosus, sartorius, and gracilis

muscles. Rotation of the tibia is limited and can occur only

when the knee is in a flexed position.

JOINT CAPSULE

The articular surfaces of the knee joint are completelyenveloped by the largest joint capsule in the body

Anteriorly, the joint capsule extends upward underneaththe patella to form the suprapatellar pouch.

The inferior portion contains the infrapatellar fat padand the infrapatellar bursa.

Medially, a thickened section of the capsule forms thedeep portion of the medial collateral ligament.

Posteriorly, the capsule forms two pouches that coverthe femoral condyles and the tibial plateau.

Synovial membrane

The synovial membrane of the knee joint attaches to

the margins of the articular surfaces and to the

superior and inferior outer margins of the menisci .

Posteriorly, the synovial membrane reflects off the

fibrous membrane of the joint capsule on either side of

the posterior cruciate ligament and loops forward

around both ligaments thereby excluding them from

the articular cavity.

Anteriorly, the synovial membrane is separated from

the patellar ligament by an infrapatellar fat pad.

In addition, the synovial membrane covering the lower

part of the infrapatellar fat pad is raised into a sharp

midline fold directed posteriorly (the infrapatellar

synovial fold), which attaches to the margin of the

intercondylar fossa of the femur.

The synovial membrane of the knee joint forms

pouches in two locations to provide low friction

surfaces for the movement of tendons associated with

the joint:

the smallest of these expansions is the subpopliteal

recess which extends posterolaterally from the

articular cavity and lies between the lateral meniscus

and the tendon of the popliteus muscle, which passes

through the joint capsule;

the second expansion is the suprapatellar bursa a

large bursa that is a continuation of the articular cavity

superiorly between the distal end of the shaft of femur

and Thigh Synovial membrane of the knee joint and

associated bursae.

Locking Mechanism

When standing, the knee joint is locked into position,

thereby reducing the amount of muscle work needed to

maintain the standing position.

One component of the locking mechanism is a change in

the shape and size of the femoral surfaces that articulate

with the tibia:

in flexion, the surfaces are the curved and rounded

areas on the posterior aspects of the femoral condyles;

as the knee is extended, the surfaces move to the broad

and flat areas on the inferior aspects of the femoral

condyles.

Consequently the joint surfaces become larger and more

stable in extension.

Another component of the locking mechanism is medial

rotation of the femur on the tibia during extension.

Medial rotation and full extension tightens all the

associated ligaments.

Another feature that keeps the knee extended when

standing is that the body's center of gravity is positioned

along a vertical line that passes anterior to the knee joint.

STABILIZING LIGAMENTS

The major stabilizing ligaments of the knee are the cruciateligaments, the collateral ligaments, and the capsularligaments.

The cruciate ligaments account for a considerable amountof knee stability. They are two ligamentous bands thatcross one another within the joint capsule of the knee.

The anterior cruciate ligament (ACL) attaches below andin front of the tibia; then, passing backward, it attacheslaterally to the inner surface of the lateral condyle.

The posterior cruciate ligament (PCL), the stronger ofthe two, crosses from the back of the tibia in an upward,forward, and medial direction and attaches to the anteriorportion of the lateral surface of the medial condyle of thefemur

Anterior Cruciate Ligament comprises three twistedbands: the anteromedial, intermediate, andposterolateral bands.

In general, the anterior cruciate ligament prevents thefemur from moving posteriorly during weight bearingand limits anterior translation of the tibia in non–weightbearing. It also stabilizes the tibia against excessiveinternal rotation and serves as a secondary restraint forvalgus or varus stress with collateral ligament damage.

When the knee is fully extended, the posterolateralsection of the cruciate ligament is most tight.

In flexion the posterolateral fibers loosen and theanteromedial fibers tighten. The anterior cruciateligament works in conjunction with the thigh muscles,especially the hamstring muscle group, to stabilize theknee joint.

Posterior Cruciate Ligament Some portion of the posterior cruciate ligament is taut throughout the full range of motion. In general, the posterior cruciate ligament resists internal rotation of the tibia, prevents hyperextension of the knee, limits anterior translation of the femur during weight bearing, and limits posterior translation of the tibia in non–weight bearing.

Capsular and Collateral Ligaments Additional stabilization of the knee is provided by the capsular and collateral ligaments. Besides providing stability, they also direct movement in a correct path. Although they move in synchrony, they are divided into the medial and lateral complexes.

Medial Collateral Ligament The superficial position ofthe medial (tibial) collateral ligament (MCL) is separatefrom the deeper capsular ligament at the joint line.

It attaches above the joint line on the medial epicondyle ofthe femur and below on the tibia, just beneath theattachment of the pes anserinus.

The posterior aspect of the ligament blends into the deepposterior capsular ligament and semimembranous muscle.Fibers of the semimembranous muscle go through thecapsule and attach to the posterior aspect of the medialmeniscus, pulling it backward during knee flexion.

Its major purpose is to prevent the knee from valgus andexternal rotating forces.

Lateral Collateral Ligament and Related Structures

The lateral (fibular) collateral ligament (LCL) is a round,fibrous cord that is about the size of a pencil. It isattached to the lateral epicondyle of the femur and tothe head of the fibula. The lateral collateral ligament istaut during knee extension but relaxed during flexion.

The arcuate ligament is formed by a thickening of theposterior articular capsule. Its posterior aspect attachesto the fascia of the popliteal muscle and the posteriorhorn of the lateral meniscus.

Other structures that stabilize the knee laterally are theiliotibial band, popliteus muscle, and biceps femoris.

BURSAE

A bursa is composed of pieces of synovial tissueseparated by a thin fi lm of fluid. The function of abursa is to reduce the friction between anatomicalstructures.

Bursae are found between muscle and bone, tendonand bone, tendon and ligament, and so forth.

As many as two dozen bursae have been identifiedaround the knee joint. The suprapatellar, prepatellar,infrapatellar, pretibial, and gastrocnemius bursaeare perhaps the most commonly injured about theknee joint.

Sciatic nerve

The sciatic nerve is a branch of the lumbosacral plexus(spinal cord segments L4-S3) and descends into theposterior compartment of thigh from the gluteal region ).

In the posterior compartment of thigh, the sciatic nervelies on the adductor magnus muscle and is crossed bythe long head of biceps femoris muscle.

Proximal to the knee, the sciatic nerve divides into itstwo terminal branches: the tibial nerve and thecommon fibular nerve.

These nerves travel vertically down the thigh and enterthe popliteal fossa posterior to the knee. Here, they meetthe popliteal artery and vein.

Nerve Supply

The tibial nerve innervates most of the hamstrings andthe gastrocnemius.

The common peroneal nerve innervates the short headof the biceps femoris and then courses through thepopliteal fossa and wraps around the proximal head ofthe fibula.

Because the peroneal nerve is exposed at the head ofthe fi bula, contusion of the nerve can cause distalsensory and motor deficits.

Leg Alignment Deviations That May Predispose to Injury Four major leg deviations could adversely affect the knee and patellofemoral joints: patellar malalignment,

genu valgum (knockknees),

Genu varum (bowlegs),

and genu recurvatum(hyperextended knees).

Patellar malalignment In patella alta, the patella sets in a more superior position than normal when the patient is standing. The ratio of patellar tendon length to the height of the patella is greater than the normal 1:1 ratio. In patella alta, the length of the patellar tendon is 20 percent greater than the height of the patella.

In patella baja ,the patella sets in a more inferior position than normal and the ratio of patellar tendon length to the height of the patella is less than the normal 1:1 ratio.

Medial Collateral Ligament Sprain

Etiology Most knee sprains affect the MCL from

either a direct blow from the lateral side in a medial

direction (valgus force) or from lateral tibial rotation.

Lateral Collateral Ligament Sprain Sprain of the lateral

collateral ligament of the knee is much less prevalent than

sprain of the medial collateral ligament.

Etiology The force required to tear this ligament is varus,

often with the tibia internally rotated

Anterior Cruciate Ligament Sprain

Etiology The anterior cruciate ligament sprain is generallyconsidered to be the most serious ligament injury in theknee.

The ACL is most vulnerable to injury when the tibia isexternally rotated and the knee is in a valgus position. TheACL can sustain injury from a direct blow to the knee orfrom a noncontact single-plane force.

Posterior Cruciate Ligament Sprain The PCL has beencalled the most important ligament in the knee, providing acentral axis for rotation. The PCL provides about 95percent of the total restraining force to straight posteriordisplacement of the tibia.

Etiology The PCL is most at risk when the knee is flexedto 90 degrees. A fall with full weight on the anterior aspectof the bent knee with the foot in plantar flexion or receipt ofa hard blow to the front of the bent knee can tear the PCL

Meniscal Lesions

The medial meniscus has a much higher incidence ofinjury than does the lateral meniscus The lateral meniscusdoes not attach to the capsular ligament and is moremobile during knee movement. Because of the attachmentto the medial structures, the medial meniscus is prone todisruption from valgus and torsional forces.

Etiology A valgus force can adduct the knee, oftentearing and stretching the medial collateral ligament;meanwhile, its fibers twist the medial meniscus outward.Repeated mild sprains reduce the strength of the knee toa state favourable for a cartilaginous tear by lessening itsnormal ligamentous stability.

The most common mechanism is weight bearingcombined with a rotary force while the knee is extendedor flexed. If an individual makes a cutting motion whilerunning, it can distort the medial meniscus.

Stretching of the anterior and posterior horns of themeniscus can produce a verticallongitudinal, or “bucket-handle” tear. Another way that a longitudinal tear occursis if the knee is forcefully extended from a flexed positionwhile the femur is internally rotated.

During extension, the medial meniscus is suddenlypulled back, causing the tear. In contrast, the lateralmeniscus can sustain an oblique tear by a forceful kneeextension with the femur externally rotated. Theseoblique tears are sometimes referred to as “parrot beak”tears and occur in the inner periphery of the meniscus.

A large number of medial meniscus lesions are theoutcome of a sudden, strong internal rotation of thefemur with a partially flexed knee while the foot is firmlyplanted.

The force of this action pulls the meniscus out of itsnormal bed and pinches it between the femoral condyles.

Meniscal lesions can be longitudinal, oblique, ortransverse. Because of the blood supply of a meniscus,tears in the outer one-third of the meniscus may healover time if stress in the area is a minimized.

Valgus force → medial collateral ligament rupture. If the force continues- medial meniscus injury and with further force ACL rupture

Varus force → lateral collateral ligament injury

Hyperextension force → ACL injury

Fall on to flexed knee/ dashboard injury → PCL injury

Forceful internal rotation → lateral meniscus injury

Forceful external rotation → medial meniscus injury

Hyperflexion (squatting) → meniscus injury (posterior horn)

INTRA ARTICULAR INJECTION

Bursitis Bursitis in the knee can be acute, chronic, or recurrent. Although any one of the numerous knee bursae can become infl amed, anteriorly the prepatellar, deep infrapatellar, and suprapatellar bursae have the highest incidence of irritation.

Etiology The prepatellar bursa often becomes inflamed from placing pressure on the front of the knee while kneeling, and the deep infrapatellar bursa becomes irritated from overuse of the patellar tendon.

Symptoms and signs Prepatellar bursitis results in localized swelling above the knee that is ballotable. Swelling is not intraarticular, and there may be some redness and increased temperature.

Swelling in the popliteal fossa could be a sign of a Baker’s cyst. A Baker’s cyst is associated with the semimembranosus bursa and occurs under the medial head of the gastrocnemius muscle. It is connected directly to the joint, and it swells because of a problem in the joint, not because of bursitis.

A Baker’s cyst is commonly painless, causing no discomfort or disability. Some inflamed bursae may be painful and disabling because of the swelling and should be treated accordingly.

LOCALIZED SWELLING

Anterior aspect of the knee

Prepatellar bursitis

Infrapatellar bursitis

Lateral aspect of the knee

Lateral meniscal cyst

Posteromedially

Semimembranosus bursitis

Posteriorly

Baker’s cyst

Popliteal aneurysm

Q ANGLE

An angle found by drawing a line from ASIS to middle of patella and a second line from mid patella to tibial tuberosityRepresents efficiency of QuadsMales range from 10-14Females from 15-17

Great than 17 degrees knock knees

Very small angle causes genu varum

References

• Clinical Neuroanatomy, Snell’s

• Gray’s Anatomy

• Snell’s Anatomy