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.