Instrumented evaluation of knee laxity: a comparison of five arthrometers

We performed a prospective study on 50 subjects with normal knees and 50 patients with chronic unilateral disruption of the anterior cruciate ligament. In a randomized testing sequence, both groups were examined with five arthrometers: the MEDmetric KT-1000, the Stryker Knee Laxity Tester, the Acufex Knee Signature System, the Dyonics Dynamic Cruciate Tester, and the Genucom Knee Analysis System. Each examination was performed according to protocol with the knee at 30 degrees of flexion. The total anterior laxity measurements of the normal subjects using the Dyonics Dynamic Cruciate Tester and Acufex Knee Signature System were approximately half of the KT-1000, Stryker, and Genucom values. A comparison of the side-to-side measurements revealed no statistically significant difference in the values of the five arthrometers. However, the Genucom showed an unacceptably high number of normal subjects with laxity values that suggested an anterior cruciate ligament tear. Total anterior laxity measurements of the anterior cruciate ligament deficient knees were almost twice those of normal knees with each device except the Genucom. Comparison of the mean side-to-side difference in the patients with ACL deficiency demonstrated statistically significant differences in the values recorded with the five arthrometers. The side-to-side difference was greatest with the KT-1000 and least for the KSS. In the 89 N Lachman test, the KT-1000 and Stryker demonstrated the highest diagnostic accuracy. The maximum manual test improved the accuracy of each device. This study establishes the total anterior laxity measurements cannot be generalized from one device to another in either group of subjects.(ABSTRACT TRUNCATED AT 250 WORDS)