Fluoroscopic and Computed Tomographic Analysis of Knee Kinematics During Very Deep Flexion After Total Knee Arthroplasty

We examined the relative motion of femoral and tibial total knee arthroplasty components and the difference between 2 different tibial inserts (9 flat types and 7 dish types) in patients sitting in very deep flexion. X-ray, fluoroscopic examination, and computed tomography were used to analyze liftoff, and rotation. During seiza-style sitting, one knee (11%) with the flat insert lifted off on the medial side and 5 knees (71%) with the dish-type insert showed liftoff. The tibial internal rotation angles were 17.2° ± 4.1° (flat type) and 11.7° ± 3.1° (dish type) (P < .05). The flat type showed less liftoff at the medial side and more internal rotation. For very deep flexion, components that tolerate larger rotational freedom are favorable.