Static load response of the heels of SACH feet

Excessive heel hardness in the prosthetic foot is a frequent problem that may contribute to decreased function in the above knee and below knee amputee. Optimal mechanical characteristics of the SACH (solid ankle cushion heel) foot have not been defined. In an effort to characterize the mechanical properties of the heels of these feet, we performed static load-deformation tests on the heels of SACH feet at stimulated heelstrike. These data were interpreted using least squares fitting of the natural logarithms of the load-deformation data. Statistical comparison of these data revealed no significant difference in the static response of the "medium" and "regular" grades of foot. A difference at the 1% level of confidence was found between the "soft" grade and the two firmer grades. Consistency within a grade of foot was quite good. Comparison of feet from another manufacturer revealed no difference in static response, suggesting consistency in static performance among manufactures. It was our clinical impression that all grades of SACH heels are too stiff.