The effect of exercise on laxity in the anterior cruciate ligament deficient knee

Twenty-five ACL deficient patients (12 males, 13 females) were compared with 20 normal controls (10 males, 10 females) to assess the effect of a known workload on AP laxity in the ACL deficient knee. The workload was predetermined, and the exercise was performed for 20 minutes on a bicycle ergometer. Both the control and ACL deficient knees demonstrated significantly increased averaged laxity after exercise. The percentage increase was less in the ACL deficient knees than in the control knees; the difference was not statistically significant. Nor was there a significant sex effect. We believe that an ACL stress test would be useful to predict which patients with documented knee instability would consequently be "at risk" of suffering disability during activity. Further investigation should be carried out to establish a stress test that would accurately define a threshold for ACL disability and indicate the need for early reconstruction in those patients at risk.