High-flexion rotating-platform knees: rationale, design, and patient selection.

High flexion in total knee arthroplasty (TKA) is any flexion beyond 125 degrees. High-flexion activities such as kneeling or praying are done with internal rotation, external rotation, and in neutral. Therefore, maximum flexion TKA requires a rotating platform. Superior range of motion (ROM) and fluoroscopic kinematics of femoral roll-back have been shown with the P.F.C. Sigma RP posterior-stabilized knee. This knee was modified to reduce the P.F.C. Sigma RP-F, a maximum flexion knee, by adding a third contact area at the post-cam mechanism to significantly increase bearing conformity and decrease polyethylene stresses in the range of 125 degrees-155 degrees. Clinical experience is reported with statistically significant increases in postoperative ROM in patients with the P.F.C. Sigma RP-F. Patient selection criteria for the P.F.C. Sigma RP-F include patients with high-flexion lifestyles, younger, more active patients demanding a better ROM, and those patients with less than 100 degrees preoperative ROM. This knee system shows significant promise in providing maximum flexion, and system longevity is expected.