Joint position sense in the normal and pathologic knee joint.

Joint position sense has been suggested to be an important factor in the etiology of degenerative joint disease. It is also believed to be important in the rehabilitative process after reconstructive surgery of the knee. Despite this awareness, in many areas of orthopaedic surgery little effort has been devoted to study of this crucial topic. Therefore, we conducted several studies of knee joint position sense by measuring the ability of healthy subjects to reproduce an angle and detect the threshold of motion. Our goal was to evaluate the effects of the following factors: aging; degenerative joint disease; total knee replacement, i.e., both absence of the anterior cruciate ligament (ACL) and sensory loss due to the absence of capsular structures; fatigue; athletic training; disruption and reconstruction of the ACL; and the role of ligament mechanoreceptors. Our results show that normal individuals can actively reproduce an angle with their knee to an average error of 2.5°. Furthermore, normal subjects require passive movement of ∼2.5°-4° to detect a change in position at the speeds used in this study (∼0.5°/s). Muscular training improves the ability to detect motion. On the other hand, muscular training and fatigue appear to decrease the ability to reproduce an angle. Changes in the knee and its associated structures caused by damage (ACL disruption, arthritis, total knee replacement) as well as aging uniformly cause deterioration of joint position sense. Total knee replacement and arthritic change cause the greatest deterioration. Reconstruction of ligamentous structures and/or rehabilitation appears to restore joint position sense to a near normal level.