Investigating the Effect of Vibrotactile Feedback in Transfemoral Amputee With and Without Movable Ankle Joint

The loss of somatosensory feedback after transfemoral amputation imposes a serious challenge in achieving postural stability. In the recent past, weight shifting exercises with fixed ankle joint have been reported useful in boosting the limit of stability (LOS) only in the sound limb; the LOS on the prosthetic limb did not improve. A fixed ankle joint restricts movement in the anteriorposterior direction at the ankle level. Thus, it may suppress the ability to move forward LOS despite awareness of center of pressure (COP) due to vibrotactile feedback. Therefore, it could have limited the improvement in the LOS of a prosthetic limb in previous studies. This article investigates this hypothesis by evaluating the effect of vibrotactile feedback in the LOS of transfemoral amputees with fixed as well as movable ankle joints. This evaluation is done during weight shifting exercises. Firstly, we developed an in-house COP guided vibrotactile sensory feedback system. Next, we recruited five transfemoral amputees to perform a weight-shifting exercise with a) fixed ankle joint (single-axis cushion heel (SACH) foot) and b) movable ankle joint (single-axis foot). Finally, we analyzed the recorded center of pressure trajectory signals for the limit of stability. The findings of repeated measures ANOVA showed a marginally significant interaction (F _{(1, 4)} = 5.7, p = 0.07, ηp ² = 0.591) between ankle joint and feedback conditions during backward shifting in weight shifting exercise. Further analysis showed that during the backward shifting fixed ankle joint did not improve in the presence of vibrotactile feedback, while a marginally significant (p = 0.14) improved LOS was observed in the movable ankle joint with feedback. The findings conclude that the vibrotactile feedback is more effective in transfemoral amputees with movable ankle joint compared with fixed ankle joint.