Development of four-bar polycentric knee joint with stance-phase knee flexion.

A conventional 4-bar polycentric knee and solid ankle cushion heel foot (SACH foot) have been commonly used in developing countries. However, they cannot perform stance-phase knee flexion, which makes a person with an amputation walk unnaturally and with less stability. This research proposes a novel design of a 4-bar polycentric knee with stance-phase knee flexion ability (4BSF), which can perform both stance and swing-phase knee flexion, like able-bodied gait. In the proposed conceptual design, the instantaneous center of rotation (ICR) path is repositioned during the stance phase. The ICR was placed in front of the ground reaction force (GRF) to initiate knee flexion during the loading response. The prototype was validated by a single-subject pilot study at the Gait analysis laboratory. The results showed that a person with an amputation walks with stance-phase knee flexion using the proposed 4BSF. The maximum knee flexion angle is more than 10° during the stance phase. Furthermore, when the 4BSF was used with a SACH foot, the amount of time to achieve the foot flat was shorter, and the foot flat duration time was twice as long as the conventional 4-bar polycentric knee.