Knee Anatomy

The knee joint consists of the weight-bearing articulation between the tibia and femur and the articulation between the patella and femur, which allows the pull of the quads to be directed anteriorly over the knee to the tibia without wearing the tendon.

Menisci

The articular surfaces include the two femoral condyles and the superior aspect of the tibial condyles. Two fibrocartilaginous menisci sit on the tibia and wrap around the outside to form C-shapes.  They improve congruency between the femoral and tibial condyles during jhoint movements where the femoral surface changes from a small, curved surface in flexion to a large flat surface in extension. The medial meniscus is attached to the margin of the capsule and the MCL whereas the lateral meniscus is unattached to the capsule making it more mobile. The menisci area interconnected anteriorly by the transverse ligament and the lateral meniscus is also connected to the popliteus tendon.

Ligaments

Patellar Ligament – continuation of the quads. It is attached above to the margins and apex of the patella and below the tibial tuberosity.

Lateral Collateral Ligament – a cord-like ligament that is attached to the lateral femoral epicondyle (just above the groove for the popliteus tendon) and the lateral fibular head. It is separated from the fibrous membrane by a bursa.

Medial Collateral Ligament – a broad and flat ligament that is attached by much of its deep surface to the underlying fibrous membrane. It is attached to the medial femoral epicondyle just inferior to the adductor tubercle and the medial surface of the tibia above and behind the attachments of Sartorius, gracilis and semitendinosus.

Transverse Ligament – Connect the anterior external regions of the lateral and medial menisci within the knee joint, sitting behind the infrapatellar fat pad.

Anterior Cruciate Ligament – attaches to a facet on the anterior intercondylar area of the tibia and a facet at the posterior lateral wall of the intercondylar femoral fossa. It prevents anterior displacement of the tibia relative to the femur.

Posterior Cruciate Ligament – attaches to the posterior intercondylar area of the tibia and medial wall of the intercondylar femoral fossa. It restricts posterior displacement.

The ACL crosses the PCL laterally as they pass through the intercondylar region.

Tibiofibular Joint

This is a synovial joint between the tibia and fibular that allows very little movement. The capsule is supported by anterior and posterior tibiofibular ligaments.

Locking Mechanism

In order to reduce the amount of work required to stand, the knee joint is ‘locked’. The change in shape and size of the femoral surfaces facilitates this. In flexion, the surfaces are curved on the posterior aspect of the femoral condyles. In extension, the surfaces move anteriorly to the flat areas on the inferior aspect of the femoral condyles. Therefore the joint becomes more stable in extension due to an increase in the surface area. Additionally the femur rotates medially on the tibia leading to the associated ligaments tightening. Furthermore, in standing an individual’s centre of gravity falls anteriorly to the knee joint further reducing the work required to stand.