Biomechanical and Metabolic Comparison of Sach and Seattle Feet in Below-Knee Amputees


The effects on gait of two prosthetic feet, SACH and Seattle, were studied. Five subjects, two right-side and three leftside congenital amputees, ages 11-18, participated. 3-D motions of the hip, knee and ankle joints were charted and joint moments and powers were computed.

The major gait compensations occurred in the sagittal plane. In all subjects, a net extensor hip moment and power generation lasted through the stance phase of the prosthetic side. More work was done at the hip in the SACH condition. On the unaffected side, a net hip extensor moment likewise dominated stance. At the knee, side of amputation was important. Right-side amputees demonstrated net flexor moments during stance, with peak power generation by the knee flexors during push-off. On their unaffected (left) side a normal extensor moment dominated. In contrast, the left-side amputees had normal extensor moments and power absorption on their prosthetic sides, while their unaffected side showed dominant knee flexor activity. At the ankle, only the left-side group demonstrated dorsiflexor moments at heel-strike. Both groups showed equal plantarflexion resistance through the remainder of stance. Plantarflexion by both prosthetic feet occurred after toe-off, likely as a result of the strong hip and knee moments.

Metabolic tests showed no difference between prostheses in energy cost of walking, but those with right-side amputations demonstrated lower energy costs than their left-side counterparts. It appears that the motor strategies chosen by amputees depends on the side of amputation.

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