Improving maximum flexion with a posterior cruciate retaining total knee arthroplasty: a fluoroscopic study.

Achieving a large range of motion (ROM) is a much-desired clinical outcome after total knee arthroplasty (TKA), especially in Asian and Middle Eastern cultures. TKA design plays an important role in providing the post-operative ROM. This study investigated the kinematics of a new high-flexion posterior cruciate ligament retaining total knee replacement, featuring an enlarged posterior condylar offset and a more conforming tibiofemoral articulation. Two flexion activities were compared to determine which provides higher flexion kinematics. Sixteen North American patients with 20 total knee implants were studied using fluoroscopy and shape matching techniques. Maximum skeletal flexion during a lunge activity averaged 120 degrees +/- 11 degrees, with 11 degrees +/- 4 degrees tibial internal rotation. Kneeling activities showed 11 degrees greater average maximum skeletal flexion (131 degrees +/- 13 degrees, p < 0.05) and 1 degrees less tibial internal rotation (10 degrees +/- 4 degrees, p > 0.05) than lunge activities. We conclude that specific knee implant design features can facilitate high flexion in fixed-bearing cruciate retaining TKA, and that kneeling activities provide higher flexion than lunge activities.