Detailed kinematics of floor-sitting activities after total knee arthroplasty (TKA) have not been well explored. Knee kinematics of cross-legged sitting, seiza-sitting, and side-sitting after TKA were examined to clarify the differences in tibiofemoral kinematics of each activity.
Subjects were 40 knees in 20 osteoarthritic patients who underwent bilateral TKA with a high-flexion fixed-bearing posterior-stabilized prosthesis. Dynamic radiographs of floor-sitting activities were taken, and the knee kinematics were compared among the three activities. The patients were also divided into two groups (possible/easy group and impossible/no-try group) for each activity, and group comparisons were conducted.
The maximum implant flexion angle was significantly greater in seiza-sitting. In valgus/varus rotation, seiza-sitting demonstrated neutral rotation, while cross-legged sitting showed varus of about 10°, and side-sitting exhibited valgus. In tibial internal/external rotation, seiza-sitting demonstrated a constant rotational angle, while cross-legged sitting showed tibial internal rotation with flexion, and side-sitting exhibited tibial external rotation with flexion. The kinematic pathway during deep flexion illustrated the medial pivot pattern in cross-legged sitting, a small amount of bicondylar rollback in seiza-sitting, and the weak lateral pivot pattern in side-sitting. A greater flexion angle was the important factor for the performance of each floor-sitting activity followed by varus laxity at 10° knee flexion.
This study successfully revealed characteristic kinematic patterns of TKA knees in three floor-sitting activities. Obtaining a greater knee flexion with adequate lateral laxity is the key to enhancing postoperative floor-sitting activities.