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.
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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