We studied the performance and proprioception of the knee joint in a group of non-reconstructed anterior cruciate ligament (ACL)-deficient (n=20) patients and compared them with a group of ACL-reconstructed patients (n=18) and a group of healthy controls (n=20). Each patient was scored according to Lysholm and Tegner and was then asked to subjectively evaluate the performance of the injured knee and the degree of retropatellar discomfort. The knee joint laxity was measured. The performance was assessed based on the performance in a triple jump test and a one-leg one-step leap test. The proprioception in the knee was measured as the threshold when passive movement was detected and as the ability to reproduce a flexion angle from a start position of 60 degrees of flexion or from full extension of the knee. All tests were performed on both legs. The scoring systems and the subjective evaluation showed significant differences between the reconstructed and the non-reconstructed patients. No significant difference in knee joint laxity was found between the two groups. In the triple jump test and the one-step leap test, both groups performed significantly worse on the leg with the injured knee joint than on the non-injured leg. The proprioceptive tests showed decreased ability to recognize and reproduce a prior angle from a start position of 60 degrees. The threshold to detection of passive movement with the injured knee was significantly increased in both groups of patients. No difference was found between the dominant and non-dominant knee in the control group. When reproduction of the same angles started from full extension, the groups did not differ. These data show that decreased performance and changes in the proprioception of the knee joint accompany ACL rupture.

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