The influence of the posterior cruciate ligament in the maintenance of joint line in primary total knee arthroplasty: A radiologic study

The aim of this study was to compare 2 total knee arthroplasty (TKA) designs radiologically to determine if a posterior cruciate ligment (PCL)–substituting design led to a built-in error of elevation of the joint line postoperatively. The restoration of the true joint line is a goal in primary TKA, although its effect on outcome has not been established fully. A total of 47 patients had 56 TKAs performed by 2 surgeons using either the Howmedica Kinemax Plus (Rutherford, NJ) PCL-retaining or PCL-substituting TKAs. The patients were randomized to receive one of these designs, and the height of the joint line was assessed radiographically preoperatively and postoperatively. The joint line position preoperatively averaged 2.2 cm from the tibial tuberosity and postoperatively averaged 2.4 cm (PCL substituting) and 2.5 cm (PCL sparing). No difference in the thickness of the polyethylene insert used was seen with either design. The theoretical elevation of the joint line that occurs with the sacrifice of the PCL was not found to occur radiologically.