3-DIMENSIONAL KNEE-JOINT MOVEMENTS DURING A STEP-UP - EVALUATION AFTER ANTERIOR CRUCIATE LIGAMENT RUPTURE

The three-dimensional motions of the knee were analysed during closed kinetic chain knee extension in 13 patients with unilateral chronic in jury of the anterior cruciate ligament. The patients ascended a platfo rm, and serial stereophotogrammetric roentgenograms were exposed from about 100 degrees of flexion to full extension. From a position of abo ut 100 degrees of knee flexion and 20 degrees of internal rotation, th e tibia rotated externally during the extension. Almost no tibial addu ction or abduction was observed. The tibial intercondylar eminence tra nslated laterally, distally: and anteriorly relative to the femur. In knees with absence of the anterior cruciate ligament, the intercondyla r eminence had a more posterior position compared with the contralater al normal knees. The proximal tibia was used as a fixed reference segm ent to evaluate the anteroposterior translations of a central point in the femoral condyles. The femoral point was more anteriorly displaced in the injured than in the contralateral knees. This difference might reflect increased activity of the hamstrings in the injured knees, be cause it was most pronounced at 80 degrees of flexion and decreased wi th increasing extension. In the sagittal plane, the mean helical axis was positioned close to the femoral insertion of the ligament at 80 de grees of flexion and was displaced distally and anteriorly during exte nsion. In the frontal plane, the axis had a transverse direction at 80 degrees of flexion. At close to full extension, the axis was position ed distally in the lateral condyle and proximally in the medial condyl e. In the horizontal plane, the helical axes ran slightly more anterio rly in the medial than in the lateral femoral condyle but changed incl ination at close to full extension and became almost parallel to the t ransverse axis.