Kneeling is an important aspect of daily living. Our goal was to describe the in vivo tibiofemoral kinematics during standing and kneeling after total knee arthroplasty (TKA).

Ten posterior substituting (PS) and 10 cruciate retaining (CR) TKA designs were studied in 18 patients. Radiographs were taken when standing, kneeling at 90°, and kneeling at maximal flexion. An image matching technique provided three-dimensional measurements of the femoral component position relative to the AP midpoint of the tibial baseplate.

When standing, the CR tibiofemoral contact position (medial: 7 mm ± 3; lateral: 6 mm ± 3) was more posterior than the PS design (medial: 5 mm ± 2; lateral: 5 mm ± 2). Movement from standing to kneeling at 90° produced different responses. CR knees translated anteriorly (medial: 4 mm ± 4; lateral: 2 mm ± 6), while PS knees translated posteriorly (medial: 0.2 mm ± 3; lateral: 1 mm ± 4). During kneeling, movement from 90° to maximum flexion produced posterior translation of the femur (CR medial: 5 mm ± 4: CR lateral: 5 mm ± 4; PS medial: 6 mm ± 4; PS lateral: 6 mm ± 3). The relationship between the tibiofemoral contact position and flexion angle during kneeling was more variable for CR knees (r2=0.38) than PS knees (r2=0.64), indicating that PS knees provide a more reliable AP position than CR knees.

PS knees dislocate when the arch of the femoral cam slides over the tibial post; CR knees sublux when the femoral contact position translates beyond the edge of the tibial baseplate. The distance to dislocation averaged 13 mm ± 2 for PS knees, and 20 mm±4 for CR knees.

Many patients wish to resume normal activities, including kneeling after TKA. This study provides information for surgeons and patients considering kneeling after TKA.