Stepping Asymmetry Among Individuals With Unilateral Transtibial Limb Loss Might Be Functional in Terms of Gait Stability

Background. The asymmetry in step length in prosthetic gait is often seen as a detrimental effect of the impairment; however, this asymmetry also might be a functional compensation. An advantage of a smaller step length of the nonprosthetic leg, and specifically foot forward placement (FFP), might be that it will bring the center of mass closer to the base of support of the leading foot and thus increase the backward margin of stability (BW MoS). Objective. The purpose of this study was to characterize differences in step length, FFP, and the concomitant difference in BW MoS between steps of the prosthetic and nonprosthetic legs (referred to as prosthetic and nonprosthetic steps, respectively) of people after transtibial amputation. Design. This was an observational and cross-sectional study. Methods. Ten people after transtibial amputation walked for 4 minutes on a self-paced treadmill. Step length and PEP were calculated at initial contact. The size of the BW MoS was calculated for the moment of initial contact and at the end of the double-support phase of gait. Results. Step length (5.4%) and PEP (7.9%) were shorter for the nonprosthetic step than for the prosthetic step. The BW MoS at initial contact was larger for the nonprosthetic step, but because of a significant leg X gait event interaction effect, BW MoS did not differ significantly at the end of the double-support phase. Limitations. All participants were relatively good walkers (score of E on the Special Interest Group in Amputee Medicine [SIGAM] scale). Conclusions. The smaller step length and FFP of the nonprosthetic step help to create a larger BW MoS at initial contact for the nonprosthetic step compared with the prosthetic step. Hence, step length asymmetry in people after transtibial amputation might be seen as a functional compensation to preserve BW MoS during the double-support phase to cope with the limited push-off power of the prosthetic ankle.