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.
This study reveals that the load cell offers a relatively simple and inexpensive way for clinicians and scientists to conduct research on both clinical problems and research hypotheses concerning the roll-over characteristics of feet and amputee preferences for alignments. Plotting two load cell variables simultaneously permits the examination of loading relationships that otherwise might not be detected. These methods could be employed to examine questions related to foot design, prescriptions for feet, alignment, or to quantify the gait of an amputee and monitor changes in gait during rehabilitation.
EDWARD S. NEUMANN, PHD, CP, PE, FAAOP, is affiliated with the Department of Civil and Environmental Engineering University of Nevada, Las Vegas.
JUSTIN BRINK, MSE, EI is affiliated with American Bio Engineers, Las Vegas, Nevada.
KARTHEEK YALAMANCHILI, MSE, EI is affiliated with Detroit Engineered Products, Troy, Michigan.
JOON S. LEE, PhD is affiliated with the Department of Mechanical Engineering, University of Nevada, Las Vegas.
Disclosure: The authors declare no conflict of interest.
Funding for this article was provided by the US Army Medical Research and Materiel Command (grant W81XWH-07-2-0084).
Correspondence to: Edward S. Neumann, PhD, CP, PE, FAAOP, Department of Civil and Environmental Engineering University of Nevada, Las Vegas, Box 4015, 4505 S Maryland Parkway, Las Vegas, NV 89154-4015; e-mail: Edward.email@example.com