Accuracy and Reproducibility of Instrumented Knee-Drawer Tests

Summary: Instrumented devices for knee-drawer tests have become popular in orthopaedics relatively recently. The objective of the present study was to document the effects of several parameters on the accuracy and reproduci-bility of anterior-posterior (AP) drawer measurements. An instrumented knee-drawer tester for AP laxity evaluations was constructed, based on the differential displacement method, measuring shifts of the tuberosity relative to the patella. The accuracy of the AP-shift was determined with the parallel use of a highly accurate roentgen stereo photogrammetric (RSP) measurement system on two postmortem leg specimens. The effects of relative motion be-tween patella and femur were negligible. In addition to AP shifts, significant knee flexion and tibia1 rotations occurred, although the foot and the thigh were fixed as well as possible. The differential displacement method was effective in circumventing this problem. The accuracy of the AP shift was>lo%. The reproducibility of the AP drawer parameters (shifts and compliances) was de-termined in normal subjects and patients. Tests were made to evaluate th