Use of a Load Cell and Force-Moment Analysis to Examine Transtibial Prosthesis Foot Rollover Kinetics for Anterior-Posterior Alignment Perturbations

Using four transtibial K4-level amputees as convenience subjects and six prosthetic feet, a load cell attached rigidly between the socket and pylon was used to measure loading effects on the residual limb that resulted when the prosthetic foot was perturbed 5 mm in an anterior-posterior direction from an initial alignment. By examining the relationship between normalized sagittal plane resultant forces and moments using force-moment analysis, the kinetic rollover characteristics of the feet and alignments were analyzed and compared. Additional variables examined included the angle of the line of action of the resultant force with respect to the pylon, and the distance from the load cell at which the line of action of the resultant force crossed the heel-to-toe axis of the load cell. Comparisons of the effects of the perturbations across subjects and feet revealed similar loading patterns within subjects for perturbations of the foot but noticeably different patterns across subjects and across different feet used by the same subject. For self-selected comfortable speed level walking, each subject exhibited differences in the magnitudes of the first and second peaks of the resultant forces and moments, but not all were statistically significant. Judgments of acceptable versus unacceptable alignments were not always matched by statistically significant differences.