Reproducibility of Genucom knee analysis system testing

Abstract

The Genucom knee analysis system was studied to determine the reproducibility of test results. In the first phase of the study we investigated the reproducibility of anterior/posterior stress tests at 30° and 90° of flexion and varus/valgus stress tests at 20° of flexion in 10 control subjects during three seatings on 3 sep arate days. In the second phase we studied the effect of errors in the digitization procedure (a part of the patient installation process) on anterior/posterior trans lation measurements. In the third phase we studied the reproducibility of a battery of tests in patients with chronic unilateral ACL deficient knees. The test battery was repeated 8 times on each knee on 6 separate days.

In Phase I, analysis of variance revealed no significant differences between tests within a single seating. The day-to-day variance of all subjects was not significant, but we found a significant interaction between day and subject which was due to significant day-to-day differ ences in individual subjects.

We found in Phase II that changing the location of the tibial joint line digitization points in the anterior/ posterior or proximal/distal direction affected anterior/ posterior translation measurements. Effects were larger at 30° of flexion than at 90° and when both the medial and lateral points were moved. Movement of the femoral condylar points resulted in a similar pattern of effects.

In Phase III, although we found significant differences between our two examiners, there were no significant intraexaminer test-to-test (within seating) effects. Ad ditionally, while there was no significant day-to-day variance overall, we found a significant interaction be tween day and subject. This was due to significant day- to-day differences in individual subjects.

The results indicate that since measurements vary from day-to-day, care must be taken in interpreting the meaning of a single measurement or even of repeated measurements made within a single seating. We advise meticulous care in the digitization procedure, diligence in assuring patient relaxation, and attention to detail throughout.