Dynamics of below-knee child amputee gait: SACH foot versus Flex foot.

Gait kinematics and dynamics during stance of unilateral, below-knee child amputees were analyzed for self-selected, comfortable (0.9 m s-1) and fast (1.3 m s-1) speeds with the SACH foot and the energy-storing Flex-foot prostheses. The three-dimensional movements of the lower limbs were recorded and synchronized with ground reaction forces for 12 subjects (7 girls and 5 boys, ages 6-16 yr). Each lower limb was modeled as a set of interconnected rigid links (thigh, leg, and foot) with frictionless joints (hip, knee, and ankle) to calculate moment and joint power profiles. Marked asymmetries were noted in ground reaction force, joint moment, and power profiles for the prosthetic versus the natural limb, but with the Flex foot the asymmetries were less pronounced than with the SACH foot. For the amputee wearing the Flex foot, greater moments and power were generated by the natural limb at the comfortable pace as compared to the SACH foot, but during fast walking, the SACH foot required greater output from the natural limb. With both prostheses, for the prosthetic limb the amputees used similar force, moment, and power patterns, but with significantly different amplitudes. At both speeds of walking, the Flex foot returned significantly more energy (66% at comfortable and 70% at fast walking) than the SACH foot (21% at comfortable and 19% at fast walking). Thus, the Flex foot had a greater potential for reducing the energy cost of walking at comfortable and fast speeds for the below-knee child amputee.