Design may be counterproductive for optimizing flexion after TKR.

Pain-free flexion of as much as 155 degrees with stability is the ultimate goal of total knee replacement (TKR). Achieving this amount of flexion depends on implant design, surgical technique, preoperative range of motion (ROM), and patient cooperation. Current design trends are focusing on shortening the radii of curvature; such shortening, in turn, thickens the posterior femoral condyle, and increases the height of the posterior-stabilized box, both of which require removal of more bone. The end results may be excessive wear, increased patellofemoral complications, and difficult revisions. Several studies have indicated preoperative ROM is more predictive of postoperative ROM than any other criteria, including implant design. Based on currently available information, if full or almost full preoperative ROM is required for the high flex total knee design, few patients would qualify for the high flex TKA.