Knee joint ; functions and structure

STRUCTURE AND FUNCTION OF THE KNEE

The bones of the knee joint consist of the distal femur with its two condyles, the proximal tibia with its two tibial plateaus, and the large sesamoid bone in the quadriceps tendon, the patella. It is a complex joint both anatomically and biomechanically. The proximal tibiofibular joint is anatomically close to the knee but is enclosed in a separate joint capsule and functions with the ankle.

JOINTS OF THE KNEE COMPLEX

A lax joint capsule encloses two articulations: the  tibiofemoral and the patellofemoral joints. Recesses from the capsule form the suprapatellar, subpopliteal, and gastrocnemius bursae. Folds or thickenings in the synovium persist from embryologic tissue in up to 60% of individuals and may become symptomatic with microtrauma or macrotrauma.

Knee joint


Tibiofemoral Joint

Characteristics

 The knee joint is a biaxial, modified hinge joint with two interposed menisci supported by ligaments and muscles. Anteroposterior stability is provided by the cruciate ligaments; mediolateral stability is provided by the medial (tibial) and lateral (fibular) collateral ligaments, respectively. The convex bony partner is composed of two asymmetrical condyles on the distal end of the femur. The medial condyle is longer than the lateral condyle, which contributes to the locking mechanism at the knee. The concave bony partner is composed of two tibial plateaus on the proximal tibia with their respective. fibrocartilaginous menisci. The medial plateau is larger than the lateral plateau. The menisci improve the congruency of the articulating surfaces. They are connected to the tibial condyles and capsule by the coronary ligaments, to each other by the transverse ligament, and to the patella via the patellomeniscal ligaments. The medial meniscus is firmly attached to the joint capsule as well as to the medial collateral ligament, anterior and posterior cruciate ligaments, and semimembranosus muscle. The lateral meniscus attaches to the posterior cruciate ligament and the tendon of the popliteus muscle through capsular connections. Because of the relatively secure attachment of the medial meniscus compared to the lateral meniscus , it has a greater chance of sustaining a tear when there is a lateral blow to the knee fibrocartilaginous menisci. The medial plateau is larger than the lateral plateau. The menisci improve the congruency of the articulating surfaces. They are connected to the tibial condyles and capsule by the coronary ligaments, to each other by the transverse ligament, and to the patella via the patellomeniscal ligaments. The medial meniscus is firmly attached to the joint capsule as well as to the medial collateral ligament, anterior and posterior cruciate ligaments, and semimembranosus muscle. The lateral meniscus attaches to the posterior cruciate ligament and the tendon of the popliteus muscle through capsular connections.

Patellofemoral Joint

Characteristics

 The patella is a sesamoid bone in the quadriceps tendon. It articulates with the intercondylar (trochlear) groove on the anterior aspect of the distal portion of the femur. Its articulating surface is covered with smooth hyaline cartilage. The patella is embedded in the anterior portion of the joint capsule and is connected to the tibia by the ligamentum patellae. Many bursae surround the patella.

Mechanics

 As the knee flexes, the patella enters the intercondylar groove with its inferior margin making first contact and then slides caudally along the groove. With extension, the patella slides superiorly. If patellar movement is restricted, it interferes with the range of knee flexion and may contribute to an extensor lag with active knee extension.

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