Comparison between Microprocessor-Controlled Ankle/foot and Conventional Prosthetic Feet during Stair Negotiation in People with Unilateral Transtibial Amputation

By Agrawal, Vibhor; Gailey, Robert S. et al. | Journal of Rehabilitation Research & Development, July 2013 | Go to article overview

Comparison between Microprocessor-Controlled Ankle/foot and Conventional Prosthetic Feet during Stair Negotiation in People with Unilateral Transtibial Amputation


Agrawal, Vibhor, Gailey, Robert S., Gaunaurd, Ignacio A., O'Toole, Christopher, Finnieston, Adam A., Journal of Rehabilitation Research & Development


INTRODUCTION

The kinematics and kinetics of lower-limb joints during stair ambulation are different from those during level walking [1]. 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. While the physiological ankle can actively dorsiflex up to 27[degrees] during movement on stairs [1-2], prosthetic feet with solid ankle designs are fixed at 90[degrees] and those with articulated ankles and J-shaped ankle springs vary the amount of functional dorsiflexion based on their design. The Proprio foot (Ossur Inc; Reykjavik, Iceland) consists of a microprocessor-controlled ankle that can dorsiflex up to 4[degrees] during stair ascent and descent. Alimusaj et al. recently reported that the active dorsiflexion of the Proprio foot/ankle during the swing phase of stair negotiation improved knee kinematics and kinetics compared with a fixed ankle that allowed no active motion [3]. However, it is unknown whether the swing-phase dorsiflexion feature of the Proprio foot offers any advantage to users with unilateral transtibial amputation (TTA) over conventional prosthetic feet with varying degrees of stance-phase dorsiflexion during stair ascent and descent.

Few studies comparing the effects of prosthetic feet on stair mobility have been published. Torburn et al. calculated the stride characteristics of 10 subjects with traumatic amputation using five prosthetic feet during stair ascent and descent [4]. The stride characteristics were calculated by means of foot switches as subjects ascended and descended a 4-step portable staircase. During ascent, the Flex Foot (Ossur Inc) and Carbon Copy Foot (The Ohio Willow Wood Co; Mt. Sterling, Ohio) resulted in a more symmetrical gait (ratio: 1.03 and 1.05, respectively) only during the initial double-limb support phase and were significantly different than the solid ankle cushion heel (SACH) foot (ratio: 1.3). During stair descent, no significant differences in stride characteristics were found among prosthetic feet. Torburn et al. concluded that none of the five test feet was clinically more advantageous for stair ambulation. Yack et al. studied the lower-limb joint moments and powers during stair ascent with three different prosthetic feet [5]. They concluded that subjects with amputation use a hip-extensor dominant strategy on the amputated side during stair ascent, and dynamic response (DR) feet (Flex Foot and Re-Flex VSP [Ossur Inc]) are advantageous over a SACH foot because they reduce the moments and power generation at the hip joint. The only study using a microprocessor-controlled foot for stair negotiation was published by Alimusaj et al., who tested the Proprio foot with its active dorsiflexion feature, the "stair mode," turned on and turned off [3]. They reported a significant change in the hip and knee moments between the two conditions for both stair ascent and descent. They concluded that the active dorsiflexion feature improves the knee kinetics and kinematics on the amputated side during stair ambulation. While comparisons between DR and non-DR feet have been reported, no studies have investigated the differences in stair ambulation between a microprocessor-controlled foot and conventional prosthetic feet in those with TTA at two distinct functional levels.

In the United States, the Medicare Functional Classification Level (MFCL) classifies mobility of people with lower-limb loss into five functional levels, primarily based on their potential to ambulate with a prosthesis (Table 1) [6-7]. Subsequent to recommendations by manufacturer representatives and invited advisors, the Centers for Medicare and Medicaid Services committee assigned prosthetic feet to a specific MFCL K-Level (categories K1-K4 feet) based on their mechanical properties (Table 1). In the majority of cases, a person with amputation's functional classification dictates the respective category of prosthetic foot prescribed and worn. …

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