Does Cybex testing increase knee laxity after anterior cruciate ligament reconstructions?

Long-term stability of the knee after anterior cruciate ligament reconstruction is imperative. Testing protocols that use isokinetic systems are commonly performed despite controversies as to their safety. The purpose of this study was to test whether one episode of isokinetic testing would cause an increase in anterior tibial translation. Twenty-four subjects who had anterior cruciate ligament reconstructions 153 to 300 days earlier volunteered for the study. Initially, subjects walked on a treadmill at 5 km/hr for 10 minutes to test the effect of exercise on displacement measurements. One week later, subjects performed a maximal knee flexion-extension test on the Cybex dynamometer at 60, 150, and 240 deg/sec. Anterior tibial displacement at 133.5 N was obtained from force-displacement curves produced by KT-2000 arthrometer testing at nine intervals: before exercise on the treadmill, at four intervals after treadmill exercise, and at four intervals after Cybex testing. Repeated measures analysis of variance did not show a significant exercise effect, interaction between type of exercise and time interval, or change after Cybex testing for the reconstructed knee displacement, the contralateral knee displacement, or side-to-side difference. The average difference before and after Cybex testing was 0.1 mm for the reconstructed knee. In conclusion, a single Cybex test, performed at least 6 months after surgery, did not affect anterior tibial displacement in this study sample.