Fluoroscopic analysis of knee arthroplasty kinematics during deep flexion kneeling.

Achieving deep knee flexion >145 degrees is a goal of many patients receiving knee arthroplasty in Asia and the Middle East, yet it is unknown whether knees with implants move similar to the natural knee in these postures. We studied 18 of 36 consecutively operated knees that were able to flex >145 degrees using fluoroscopic analysis during kneeling to maximum flexion. An average of 9 degrees tibial internal rotation was observed in deep flexion. Posterior condylar translations were observed from 80 degrees to 120 degrees flexion, and the condyles translated forward in flexion beyond 120 degrees. Separation of the condyles from the tibial surface was observed in 9 knees at flexion >130 degrees. Very deep flexion can be achieved and is well accommodated using contemporary posterior-stabilized knee arthroplasty, but the kinematics differ from the intact natural knee.