A study in the current issue of the Journal of Rehabilitation Research & Development, Volume 50, Number 7 2013, compared microprocessor-controlled ankle/foot systems with conventional prosthetic feet during stair negotiation in people with unilateral transtibial amputations. The researchers concluded that individuals with unilateral transtibial amputation who function at either a K2 or K3 level and have to negotiate stairs on a regular basis, within their homes, communities, or work environments, may benefit from the use of microprocessor-controlled feet that allow active dorsiflexion during swing phase.
According to the study authors, the majority of prosthetic feet are designed with an emphasis on level-ground gait and do not consider the biomechanics of functional activities such as ascending and descending stairs. Further, few studies comparing the effects of prosthetic feet on stair mobility have been published, and the number of research studies investigating amputation gait on stairs is limited.
Ten individuals with unilateral transtibial amputation were enrolled in the study. They were between the ages of 43 and 64, weighed less than 255 pounds, and had been comfortable fit with a prosthesis for at least six months. All subjects could ambulate with a prosthesis on a level surface with a consistent cadence for a minimum of 200 meters and could safely negotiate stairs. Each subject received a study socket fabricated using a CAD image of the subject’s residual limb that was modified by the study prosthetist to ensure optimal fit. A suction suspension mechanism with either an Össur Iceross Seal-in liner or a cushion liner and external sleeve was used for all subjects. Each participant tested four prosthetic feet: SACH, stationary attachment flexible endoskeleton (SAFE), Talux foot (conventional prosthetic foot), and Össur PROPRIO FOOT® (microprocessor-controlled foot) Subjects received standardized, functional prosthetic gait training with their existing sockets and feet as well as with the study socket and test feet to minimize the influence of confounding variables on amputation gait. For stair ascent, each subject was instructed to place the prosthetic foot on a step, exert a downward force while extending the hip and knee to raise the body, and place the contralateral limb on the next step in a controlled manner. All subjects were able to ascend and descend the stairs leg-over-leg and were instructed to hold onto the handrail for safety and not as a means to assist with the maneuver. Cues were given to assist with the maneuver when necessary. Ground reaction forces were collected during stair ascent and descent.
The researchers concluded that the microprocessor-controlled foot resulted in significantly greater Symmetry in External Work (SEW) values between the lower limbs during stair ascent. However, during stair descent, the interlimb symmetry with the PROPRIO FOOT was not significantly better than conventional prosthetic feet. Since the dynamic response characteristics of prosthetic feet have not been shown to be advantageous while negotiating stairs, the swing-phase dorsiflexion of the microprocessor-controlled foot seems to promote kinetic symmetry between the lower limbs while ascending stairs.