The knee joint complex includes three articulating surfaces, which form two distinct joints contained within a single joint capsule: the patellofemoral and tibiofemoral joint.1,2 One of the problems facing the knee joint complex is the fact that it was not originally designed for bipedal motion.3 Evolutionary modifications have allowed the knee to adapt to the major changes placed on it during functional demands.2 Despite these adaptations, however, the knee is one of the most commonly injured joints in the body.
Despite its proximity to the tibiofemoral joint, the patellofemoral joint can be considered as its own entity, in much the same way as the craniovertebral joints are when compared to the rest of the cervical spine.
The tibiofemoral joint is a ginglymoid, or modified hinge joint, which has six degrees of freedom. The bony configuration of the knee joint complex is geometrically incongruous and lends little inherent stability to the joint.
Joint stability of the knee is dependent upon the static restraints of the joint capsule, ligaments, and menisci, and the dynamic restraints of the quadriceps, hamstrings, and gastrocnemius.4,5