Factors contributing to function of the knee joint after injury or reconstruction of the anterior cruciate ligament.

Restoration of musculoskeletal function is a fundamental goal of orthopaedic treatment. Until now, clinical orthopaedic concepts of injury, repair, and restoration of function of musculoskeletal systems have been described and understood primarily in structural and biomechanical terms. This perception probably evolved because the structural characteristics are the most readily visualized factors, both in the clinical setting (for example, pathological laxity due to a ruptured ligament or a fracture) and through the preponderance of structural and pathoanatomical data offered by most current imaging modalities. Structural characteristics are also the factors most directly altered by operative intervention, such as stability following repair or reconstruction of a ligament or fixation of a fracture. It is a common belief that the restoration of measurable structural and biomechanical parameters to an injured joint, such as the knee, indicates the restoration of function to that system. We do not share this view. In the past few years, emerging clinical and basicscience findings have indicated a much greater degree of underlying biological complexity. Evidence suggests that the correction of identifiable structural abnormalities is often not sufficient to restore a joint to its full preinjury level of physiological function. For example, replacement of a ruptured anterior cruciate ligament with a graft does not necessarily prevent pain, swelling, or degenerative changes in the knee, even if the increased anterior-posterior laxity that had been present before the procedure is restored to normal. This observation indicates that factors other than anatomical and structural ones probably contribute to the restoration of joint function after injury. We believe that, although these other factors are less easily visualized, they play an important role in the ultimate functional status of an injured musculoskeletal system, such as the knee. The purpose of this Instructional Course Lecture is to discuss the concept of musculoskeletal function and to consider the various factors that contribute to the restoration of knee function after injury or reconstruction of the anterior cruciate ligament.