Socket Reaction Moment Impulse May Assist in Alignment Tuning Process of Transtibial Prostheses

Currently, the appropriate range of socket reaction moment impulse for effective prosthetic gait and care of the residual limb is unknown. However, socket reaction moment impulse could potentially serve as a valuable parameter to assist the alignment tuning process of the transtibial prostheses, according to recent study results published in Journal of Biomechanics.

“Moment impulse incorporates both the magnitude of moment and its duration time (moment-time integral). This measurement has been used to investigate the effect of orthotic interventions on patients with knee osteoarthritis,” Toshiki Kobayashi, PhD, a research scientist at Orthocare Innovations, told O&P Business News. “We applied this technique to quantify the effect of alignment changes on residual limb loading. The advantage of using the moment impulse is to enable quantification of a ‘dose-response’ like effect of prosthetic alignment. In this study, the dose is alignment, while response is socket reaction moment impulse. Thus, the purpose of this study was to investigate the effects of alignment changes on the socket reaction moment impulse in transtibial prostheses using an instrumented pyramid adaptor.”

Measuring alignment with Smart Pyramid

Researchers measured the socket reaction moment impulse at a self-selected walking speed in 10 amputees with transtibial prostheses using a Europa Smart Pyramid (Orthocare Innovations, Mountlake Terrace, Wash.) in 25 alignment conditions, including a nominal alignment, angle malalignments of 2°, 4° and 6° and translation malalignments of 5 mm, 10 mm and 15 mm. For each condition, researchers compared the socket reaction moment impulse to the nominal alignment.

Toshiki Kobayashi


In comparison to the nominally aligned condition, researchers found both angle and translation alignment changes induced significant differences at all malaligned conditions for the varus socket reaction moment impulse. Although changes in sagittal angle alignment did not induce any significant differences in malaligned conditions for the extension and flexion socket reaction moment impulse, study results showed significant differences in translation alignment changes in all malaligned conditions for the extension socket reaction moment impulse, as well as some malaligned conditions for the flexion socket reaction moment impulse. 

“The results of our study mean that prosthetists can now quantify the effect of prosthetic alignment on the residual limb loading using the Europa in the clinical setting,” Kobayashi said.

Research on prosthetic alignment

According to Kobayashi, while alignment is important for a successful prosthetic fit, it receives the least attention in research.

“There are many research projects currently undergoing about prosthetic sockets, feet and joints, but not enough research is performed on prosthetic alignment,” Kobayashi said. “Because these novel prosthetic components perform much better than before and require greater control by the prosthetic user, prosthetic alignment needs to be performed at a much more precise level. Prosthetic alignment needs more research, and I hope that our research will be a vehicle to drive prosthetic alignment research in a clinically relevant manner.”

In the future, Kobayashi and colleagues are interested in monitoring the loading on the residual limb and investigating its relationship with residual limb health, as well as investigating the effect of different prosthetic components, such as feet, socket and joint, on the residual limb loading. — by Casey Tingle

For more information:
Kobayashi T. J Biomech. 2014;47:1315-1323.

Disclosures: Boone, Kobayashi, Orendurff, and Rosenbaum-Chou are employees of Orthocare Innovations LLC, the manufacturers of Europa.

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