Discuss the Classification of Knee Joint

KNEE JOINT LEARNING OBJECTIVES

• Discuss the classification of knee joint • Describe the articular surfaces of this joint • Discuss the articular capsule • Learn about the synovial membrane and the synovial cavity • Enumerate the ligaments of knee joint • Describe the bursa around the knee joint • Describe the blood and nerve supply of the knee joint CLASSIFICATION OF KNEE JOINT

• The knee or Genual Joint is formed between lower end of femur, the upper end of tibia and the posterior surface of patella. • Between anterior surface of lower end of femur and posterior surface of patella is Gliding Synovial variety • Between inferior surface of condyles of femur and superior surface of condyles of tibia is hinge variety of synovial joint.

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.  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 plateau, are separated from each other by a narrow, nonarticular area, which widens anteriorly and posteriorly into anterior and posterior intercondylar areas, respectively.

LIGAMENTS 1. Fibrous capsule 2. Ligamentum patellae 3. Tibial colletral or medial ligament 4. Fibular collateral or Lateral ligament 5. Oblique popliteal ligament 6. Arcuate popliteal ligament 7. Anterior cruciate ligament 8. Posterior cruciate ligament 9. Medial meniscus 10.Lateral meniscus 11.Transverse ligament ARTICULAR CAPSULE OF THE KNEE

• The fibrous capsule is strong, especially where local thickenings of it forms ligaments. • Superiorly, the fibrous capsule is attached to the femur, just proximal to the articular margins of the condyles • Posteriorly, it is attached to the intercondylar line. • 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; 1. patellar ligament 2. fibular collateral ligament 3. tibial collateral ligament 4. oblique popliteal ligament 5. arcuate popliteal ligament SYNOVIAL MEMBRANE

• The synovial membrane of the knee-joint is the largest and most extensive in the body. • Commencing at the upper border of the patella, it forms a large cul-de-sac beneath the Quadriceps femoris on the lower part of the front of the femur • Frequently communicates with a bursa interposed between the tendon and the front of the femur. • The pouch of synovial membrane between the Quadriceps and front of the femur is supported, during the movements of the knee, by a small muscle, the Articularis genu, which is inserted into it. 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.

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

FIBULAR COLLATERAL LIGAMENT

• The fibular collateral ligament (lateral ligament) is a round 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. 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.

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

• The cruciate 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. • 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 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.

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, is slack when the knee is flexed and taut when it is fully extended • Prevents posterior displacement of the femur on the tibia on 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.

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 stabilizing factor for the femur, e.g., when walking downhill or downstairs. MENISCI OF 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 rest on the tibial condyles and 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 fibers 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.

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. 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 KNEE

 Several bursa are present around the knee, to reduce friction, because most tendons around the knee joint run parallel to the bones and pull lengthwise across the joint.  Four bursa communicate with the synovial cavity of the knee joint; they lie deep to the tendons of : o The quadriceps femoris o The popliteus o The medial head of the gastrocnemius muscle. • There are around 13 bursae • Anterior: 4 bursae à Subcutaneous prepatellar bursa à Subcutaneous infra patellar bursa à Deep infrapatellar bursa à Suprapatellar bursa • Lateral: 4 bursae • Medial: 5 bursae 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 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 articularis genu muscle.

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.  Inflammation of this is "housemaid's knee". 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).  Inflammation of this bursa is "clergyman's knee" BLOOD SUPPLY

• Supplied by the anastomoses around it: 1. Five genicular branches of the popliteal artery 2. Descending genicular branch of the femoral artery 3. Descending branch of the lateral circumflex femoral artery 4. Two recurrent branches of the anterior tibial artery 5. Circumflex fibular branch of the posterior tibial artery

NERVE SUPPLY

 Femoral nerve, through its branches to the vasti.  Sciatic nerve, through its genicular branches of the tibial and commom peroneal nerves.  Obturator nerve, through its post division.