POSITION OF THE KNEE-JOINT AFTER TOTAL JOINT ARTHROPLASTY

A method for assessing knee joint position after surgery using the pre operative long-leg radiograph and the postoperative knee radiograph is described. Assessment of the formula has shown a near perfect correla tion between the calculated position on the long-leg radiograph compar ed with the measured position for 44 knees. Three hundred eighteen kne es after total joint arthroplasty were retrospectively reviewed and th e postoperative position was determined. The preoperative position of the mechanical axis was 14.5 +/- 37.3 mm medial to the knee joint cent er. Using the standing knee radiograph the postoperative position of t he mechanical axis was 3.07 +/- 9.2 mm lateral to the knee joint cente r, while the portable radiograph placed the mechanical axis 4.5 +/- 12 .4 mm medial to the knee joint center. There was a highly significant difference in the position of the knee joint center depending on the r adiograph used for calculation (standing or portable). The difference between the two means was not due to opening of the kneejoint, but lik ely due to change in the rotation of the knee in the presence of knee flexion. This series of the knee arthroplasties has a low projected ra te of aseptic failure.