Muscle Function and Coordination of Amputee Stair Ascent

Ascending stairs is challenging following transtibial amputation due to the loss of the ankle muscles, which are critical to human movement. Efforts to improve stair ascent following amputation are hindered by the limited understanding of how the prosthesis and remaining muscles contribute to stair ascent. This study developed a three-dimensional (3D) muscle-actuated forward dynamics simulation of amputee stair ascent to identify the contributions of individual muscles and the passive prosthesis to the biomechanical subtasks of stair ascent. The prosthesis was found to provide vertical propulsion throughout stair ascent, similar to nonamputee plantarflexors. However, the timing differed considerably. The prosthesis also contributed to braking, similar to the nonamputee soleus, but to a greater extent. However, the prosthesis was unable to replicate the functions of nonamputee gastrocnemius, which contributes to forward propulsion during the second half of stance and leg swing initiation. To compensate, the hamstrings and vasti of the residual leg increased their contributions to forward propulsion during the first and second halves of stance, respectively. The prosthesis also contributed to medial control, consistent with the nonamputee soleus but not gastrocnemius. Therefore, prosthesis designs that provide additional vertical propulsion as well as forward propulsion, lateral control, and leg swing initiation at appropriate points in the gait cycle could improve amputee stair ascent. However, because nonamputee soleus and gastrocnemius contribute oppositely to many subtasks, it may be necessary to couple the prosthesis, which functions most similarly to soleus, with targeted rehabilitation programs focused on muscle groups that can compensate for gastrocnemius.