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Proprioception in the anteriorly unstable knee.

Despite the anterior cruciate ligament (ACL) being the most frequently injured knee ligament22, the literature suggests a wide range of resulting dysfunction and discrepant treatment. Dysfunction consists of limitation of activities of daily living and recreational activities due to pain, swelling and "giving-way" of the knee35. Two distinct, yet not mutually exclusive, viewpoints may account for dysfunction following ACL injury. In the "structural paradigm" , dysfunction results from lack of restraint to anterior subluxation of the tibia on the femur 8,11,15,19,20,21,25,26,30,31. In the "neurosensory paradigm", dysfunction results from loss of critical sensory input' '3 713,24,39 40. That is, neural pathways originating in the ACL contribute to a sense of "proprioception", allowing for reflex or supraspinal initiation of stabilizing muscle contraction about the knee. Proprioception, in its strictest sense, is an awareness of limb location in space42, reflected by the ability to reproduce limb position. Today this definition is often expanded to include the awareness of limb movement. When proprioceptive sense is lost, as might occur with injury to the ACL, one would be less able to detect limb movement. In 1989, Barrack et al.3 used latency to detection of passive motion as a measure of proprioception. He used this to demonstrate a proprioceptive deficit in a group of patients with unilateral, isolated, complete ACL tears. We instituted this study to confirm and extend the findings of Barrack et al. We additionally addressed the issue of dysfunction following injury by identifying the severity of symptoms and degree of functional impairment. Lastly, we explored the possibility that separate populations of mechanoreceptors may be stimulated at different rates of extension of the leg, producing varying degrees of proprioception. Therefore, we proposed the following hypotheses: 1) normal joint movement sense (proprioception) becomes abnormal following disruption of the ACL; 2) dysfunction of the knee correlates with poor proprioceptive ability; and 3) proprioceptive ability depends upon the rate of extension of the knee.