Deep flexion-oriented bisurface-type knee joint and its tibial rotation that attributes its high performance of flexion.

In 1989, we developed an artificial knee prosthesis that could accommodate the oriental lifestyle where people would sit more often on the floor than on a chair. The knee had a bisurface feature with an auxiliary joint of a ball and socket at the center of the posterior part aiming at an improved flexional function. The auxiliary joint functions not only to facilitate a rollback movement but also to add a rotational movement. It was investigated whether this knee prosthesis could show an internal rotation of the tibia during flexion such as the physiologic movement of the knee. The internal rotation of the tibia was evaluated for the patients who could sit on legs in the oriental style after total knee arthroplasty. The average flexion angle of patients who achieved this style of sitting was 144.1°, and the average internal rotation was estimated as 14.3° by a pattern matching method using a computer-assisted design system.