Prosthetic gait asymmetry when walking on an inclined treadmill

Background. Step length asymmetry is considered exclusive for measuring gait asymmetry. However asymmetries in trunk progression and forward foot placement relative to the trunk may also contribute to gait asymmetry since the sum of the two should result in step length asymmetry. This relation can be tested in a situation where increased propulsion demands are required such as in inclined walking. Especially prosthetic gait may magnify this relation since prosthetic gait is often asymmetric. Objective. To investigate the effect of inclination on (i) the relation between step length, trunk progression and forward foot placement asymmetry, and (ii) the adaptation strategies adopted by amputees to cope with altered propulsion demands. Methods. Full-body motion analysis was performed on 8 unilateral trans-tibial amputees when walking on an inclined treadmill at their comfortable speed. (Non-)Prosthetic, step length, trunk progression, forward foot placement and corresponding asymmetries were determined. Results. The asymmetries in both trunk progression plus forward foot placement were highly correlated to step length asymmetry for inclined walking. Adaptations were most prominent in forward foot placement. Inclination was negatively correlated with the average forward foot placement and positively correlated with the absolute differences in forward foot placement between the prosthetic and the non-prosthetic step. Two groups could be distinguished when looking at the direction (negative/positive) of forward foot placement asymmetry. When accounted for these groups, inclination was positively correlated to forward foot placement asymmetry. Conclusion. (i) The relation between asymmetries in step length, trunk progression and forward foot placement was unaffected by inclination. (ii) One adaptation strategy was to decreased non-prosthetic forward foot placement, however more subtle adaptations may also have played a role.