Instrumented examination of knee laxity in patients with anterior cruciate deficiency: a comparison of the KT-2000, Knee Signature System, and Genucom.

Knee ligament arthrometers are used during rehabilitation to assess changes in knee laxity after anterior cruciate ligament injury. This study investigated the reliability and error associated with measurements of knee laxity using three different instrumented devices: the KT-2000, the Knee Signature System (KSS), and the Genucom Knee Analysis System to aid in the interpretation of instrumented laxity measurements during rehabilitation. Ten subjects with unilateral anterior cruciate deficiency were examined by two testers on two separate days. Measurement error was calculated as the minimum difference required to assume a true change in laxity between two measurements (p < 0.05). Between-day reliability was relatively high for both the KSS and the KT-2000 (.95 and .83, respectively) but substantially lower for the Genucom (.22). Intertester reliability was slightly lower for the KT-2000 and the KSS (.92 and .78, respectively) and slightly higher but still low for the Genucom (.27). When monitoring changes in anterior laxity of an anterior-cruciate-deficient knee, the following error values were determined to be needed in order to assume a true difference between successive measurements: KT-2000, 2.0 mm; KSS, 4.2 mm; and Genucom, 5.9 mm. The results of this study suggest that measurements of anterior laxity taken by a single examiner using the KT-2000 provide the most reliable measurements.