Reliability of the Genucom Knee Analysis System

Instrumented knee laxity testing is now common practice in many orthopedic and rehabilitative practices around the country. The Genucom Knee Analysis System is marketed as a comprehensive quantitative knee joint laxity testing device. To examine the intrarater reliability of the Genucom, the authors evaluated five normal subjects, each on three independent occasions. All testing was done by a single examiner. Anteroposterior (AP) drawer, valgus/varus, and tibial rotation tests were performed. The average variability for repeated testing was determined and this variability was then used to estimate the smallest statistically significant difference for a single repeat examination that would represent true change, i.e., change over and above the inherent variability of the measurement. The results indicate that: (1) anterior drawer variability and tibial rotational variability are dependent on the knee flexion angle; (2) reporting anterior drawer may be more reproducible than reporting total AP motion; and (3) on average, changes exceeding 3 mm for anterior drawer tests, 5 mm for total valgus-varus motion, and 7 degrees-17 degrees of tibial rotation are needed to be 95% confident that the change in a measure from one time to the next is real and not due to measurement variability.