Effect of femoral component position on biomechanical outcomes of unicompartmental knee arthroplasty.

BACKGROUND: The positions of unicompartmental femoral components do not always follow the neutral center of the medial distal femoral condyle. The biomechanical effect of the center of the distal femoral condyle has not yet been evaluated, and the optimal femoral position in unicompartmental knee arthroplasty (UKA) is yet to be biomechanically justified. The purpose of this study was to evaluate, using finite element analysis, the effect of the center of the distal femoral component on the biomechanical outcomes of UKA with respect to the contact stresses in the polyethylene (PE) insert and articular cartilage. METHODS: Five models in which the centers of the distal femoral components were translated by three millimeters and five millimeters to the medial and lateral sides, respectively, from the neutral position were modeled and analyzed in a gait loading condition. RESULTS: The contact stresses on the PE insert increased as the center of the femoral component translated to the lateral side and, in contrast, the contact stresses decreased as it translated to the medial side. For the articular cartilage the contact stresses increased and decreased as the center of the femoral component translated to the medial and lateral sides. CONCLUSION: This study implied that the best position for the femoral component in UKA could be the center of the distal femoral condyle. Femoral component position could be one of the sensitive factors that influenced the contact stresses on the PE insert and articular cartilage, and the postoperative significance of the femoral component position in UKA.