The knee joint is the largest articulation in the body. It is a hinge joint but actually is more complicated because apart from flexion and extension its motion has a rotary component. The osseous structures, the extra-articular structures and the intra-articular structures are three factors of the stability of the knee. The patella, the distal femoral condyles and the proximal tibial plateaus or condyles are three components of osseous structures. The important extra-articular tendinous structures that give stability to the knee are the musculotendinous units principally the quadriceps mechanism, the gastrocnemius, the medial hamstrings comprising the sartorius, the semitendinosus, the gracilis and the semimembranosus, the lateral hamstring comprising the biceps femoris and the popliteus. The principal intra-articular structures are the medial and lateral menisci and the anterior and posterior cruciate ligaments. The medial meniscus is semilunar in shape with a thin anterior horn and widens posteriorly. The lateral meniscus is more mobile than the medial meniscus and is circular in shape. Anteriorly and posteriorly the menisci are attached to the tibial intercondylar area by fibrous extremities or horns.