Alignment Changes Affect Socket Reaction Moments in Transtibial Prostheses

In transtibial prostheses with energy storage and return feet, alignment changes had a systematic effect on the socket reaction moments in the sagittal and coronal planes, according to study results published in Clinical Biomechanics. Researchers believe the socket reaction moments could potentially be a useful biomechanical parameter to evaluate the alignment of the transtibial prostheses.

“Alignment is considered one of the most important factors for successful fit of lower-limb prostheses. Yet, the alignment process in the clinical setting is highly subjective, depending on prosthetists’ experience and judgment. Dynamic alignment is currently based on the prosthetists’ visual observation of the patient’s gait and the patient’s perception of comfort while walking with the prosthesis. Therefore, a clinical tool that can provide quantitative data to prosthetists about prosthetic alignment would be valuable for evidence-based practice,” Toshiki Kobayashi, PhD, research scientist at Orthocare Innovations LLC, told O&P Business News. “This study investigated the effect of alignment changes on moments — ie, socket reaction moments — measured at the base of a socket using an instrumented pyramid adaptor in transtibial prostheses. The instrumented pyramid adaptor allows prosthetists to measure kinetic data — ie, moments and forces — of gait with a prosthesis conveniently without a computerized 3-D motion analysis system. Therefore, its potential in the clinical setting is promising.”

Socket measurement


Toshiki Kobayashi

Researchers recruited 10 participants with transtibial prostheses who were daily users of energy storage and return (ESR) feet. While participants walked under 25 alignment conditions, including a nominal alignment, as well as angle malalignments of 2°, 4° and 6° and translation malalignments of 5 mm, 10 mm and 15 mm referenced from the nominal alignment, researchers used an instant socket forces measurement system (Europa, Orthocare Innovations) to measure the socket reaction moments. Socket reaction moments of the nominal alignment were then compared with each malalignment.

Study results showed both coronal and sagittal alignment changes demonstrated systematic effects on the socket reaction moments. Angle and translation changes in the sagittal plane demonstrated significant differences in the minimum moment, the moment at 45% of stance and the maximum moment for some comparisons, according to the researchers. Angle and translation alignment changes in the coronal plane demonstrated significant differences in the moment at 30% and 75% of stance for all comparisons.

“The results of this study suggested that the instrumented pyramid adaptor could provide prosthetists objective data of prosthetic alignment through the socket reaction moment,” Kobayashi said. “In the future, prosthetists can depend not only on subjective judgment, but also on objective data to justify prosthetic alignment in the clinic. Improved care of patients based on objective outcome is the key to level up the profession in the future.”

“Direct measurement of moments and forces on the prosthesis is one of the hot topics in the research field,” Kobayashi said. “I hope that the findings of these studies will contribute to improving the fitting of prostheses and, as a result, improving the quality of life of amputees.” — by Casey Tingle

For more information:
Kobayashi T. Clin Biomech. 2014;29:47-56.

Disclosure: Kobayashi is employed by Orthocare Innovations LLC, the manufacturers of Europa (formerly known as SmartPyramid).

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