Fluoroscopic validation of electrogoniometrically measured femorotibial translation in healthy and ACL deficient subjects.

Equipment which measure femorotibial motions indirectly by using a patellar pad are reported to have errors caused by deformation of soft tissues and slippage of the device. For the purpose of validation, the tibial translation in relation to the femur per degree of knee extension was estimated from the slope coefficients of the flexion-displacement curve, obtained by both fluoroscopic and electrogoniometric tests, in the knee of the dominant limb in healthy subjects and in both knees of patients with unilateral anterior cruciate ligament (ACL) deficiency. In addition, the anterior and posterior static knee laxity limits and the tibial resting position were evaluated. Within all knee groups, the tibia moved posteriorly in relation to the femur during extension. The measured movement was similar both with the electrogoniometer and with fluoroscopy thereby indicating that sagittal plane knee translation measurements with the CA-4000 electrogoniometer are reliable and in good agreement with the X-ray measurements, even though the measurements were made separately. The ACL injured knees showed approximately 20% smaller posterior movement of tibia in relation to femur per degree change of knee extension than the non-injured or control knees (p < 0.05) and a more anterior resting position of the tibia relative to femur as compared to the contralateral healthy knee during knee laxity testing (p = 0.002).