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
The two central intra-articular cruciate ligaments cross each other forming an x-pattern. Both the ACL and PCL lie in the center of the joint, and each are named according to their attachment sites on the tibia.6 These two ligaments, composed mainly of type I collagen, are the main stabilizing ligaments of the knee and restrain against anterior (ACL) and posterior (PCL) translations of the tibia on the femur. They also restrain against excessive internal and external rotation and varus movement of the tibia.7
The patellofemoral joint is composed of the articulation of the patella with the femoral condyles of the femur. The patella is a passive component of the knee extensor mechanism, where the static and dynamic relationships of the underlying tibia and femur determine the patellar-tracking pattern.
To assist in the control of the forces around the patellofemoral joint, there are a number of static and dynamic restraints.
The examination of the knee joint complex should include a thorough and detailed history, a careful inspection and palpation of the knee for point tenderness, assessment of joint effusion, range-of-motion and strength testing, an evaluation of the ligaments for injury or laxity, an assessment of patella motion, and assessment of the integrity of the menisci. Accurate diagnosis requires knowledge of knee anatomy, common pain patterns in knee injuries, frequently encountered causes of knee pain, as well as specific physical examination skills.3
Broadly speaking, acute knee injuries fall into one of six categories: ...