The effects of a controlled energy storage and return prototype prosthetic foot on transtibial amputee ambulation
Introduction
One in 190 Americans is currently living with the loss of a limb and the incidence of amputation is on the rise (Ziegler-Graham, MacKenzie, Ephraim, Travison, & Brookmeyer, 2008). Two-thirds of these amputations are of the lower limb, which often leads to limitations in functional mobility, an array of co-morbidities of the intact and residual limb joints (Gailey et al., 2008, Struyf et al., 2009) and persistent pain and discomfort (Ehde et al., 2000). The absence of plantar-flexor musculature significantly affects amputee gait by reducing ankle push-off power of the prosthetic limb, likely leading to compensations at other joints and increased loading of the intact limb compared to non-amputees (Gitter et al., 1991, Seroussi et al., 1996, Winter and Sienko, 1988). These alterations in gait may subsequently contribute to the increased metabolic cost of amputee walking compared to non-amputee walking at the same speeds (Genin et al., 2008, Waters and Mulroy, 1999) as well as contribute to the reduced self-selected walking speed, cadence and stride length (Gitter et al., 1991, Robinson et al., 1977, Torburn et al., 1990, Waters et al., 1976, Winter and Sienko, 1988).
Energy storage and return (ESR) prosthetic feet were designed to address reduced prosthetic limb push-off work by returning mechanical energy absorbed from mid to late stance, rather than dissipating it through viscoelastic deformation as with non-ESR prosthetic feet. ESR feet result in amplified peak fore-aft ground reaction forces in the prosthetic limb (Lehmann et al., 1993, Powers et al., 1994), increased prosthetic foot power and work generated (Barr et al., 1992, Gitter et al., 1991) and decreased vertical ground reaction forces in the sound limb during weight acceptance (Lehmann et al., 1993, Perry and Shanfield, 1993, Powers et al., 1994, Snyder et al., 1995) compared to more traditional prosthetic feet (i.e., SACH foot). Subjectively, many amputees prefer ESR feet (Romo, 1999) and perceive an increase in activity, velocity and stability with less pain and skin problems than with non-ESR feet (Hafner, Sanders, Czerniecki, & Fergason, 2002). However, in several studies the metabolic cost of walking (Hafner et al., 2002, Lehmann et al., 1993, Torburn et al., 1990, Versluys et al., 2009, Waters et al., 1976), preferred walking speed and gait symmetry (from Barth et al., 1992, Grabowski et al., 2010, Hsu et al., 2006, Torburn et al., 1990) have not been shown to change significantly for amputees wearing ESR feet compared to more traditional designs. The general consensus is that despite subjective preference, current ESR feet demonstrate little objective improvement in overall walking performance (Hafner et al., 2002, van der Linde et al., 2004).
Increased prosthetic ankle push-off work may improve amputee gait by minimizing compensations at other joints (Au et al., 2009, Houdijk et al., 2009, Seroussi et al., 1996). Simple walking models suggest that much of the mechanical work required for ambulation is determined by the amount of energy dissipated in the transition between steps, as the center of mass (COM) is redirected by the new stance limb (Donelan et al., 2002, Kuo et al., 2005). The appropriate magnitude and timing of trailing leg push-off is thought to reduce the collision of the leading leg, which may lead to a decrease in total COM work (Kuo, 2002, Ruina et al., 2005). Traditional prosthetic feet cause a disruption in this cycle by reducing the positive work performed by the trailing prosthetic leg at push-off, disproportionately increasing dissipation in the leading intact leg and increasing metabolic energy cost of amputee walking (Houdijk et al., 2009). Therefore, a prosthesis with increased push-off work could potentially reduce this dissipation, reduce metabolic cost and improve amputee gait.
A Controlled Energy Storage and Return (CESR) prototype prosthetic foot (Collins & Kuo, 2010), which can capture and store some of the collision energy normally dissipated at foot contact and then transfer it to the forefoot just prior to toe-off, may increase prosthetic push-off work, reduce energy loss at collision of the intact leg and reduce metabolic cost of gait. In a study of non-amputees wearing a simulator boot, a CESR foot prototype increased both average ankle push-off power and COM push-off work, decreased intact limb COM collision work, and reduced metabolic cost by 9% compared to a conventional prosthetic foot (Collins & Kuo, 2010), suggesting the potential for similar benefits in amputees.
The aim of this study was to test for biomechanical and metabolic effects of the same CESR prototype foot on transtibial amputee gait compared to a common conventional foot and to each subject’s prescribed foot. We tested whether amputees wearing this CESR prototype would exhibit: (1) increased prosthetic foot push-off power and work, (2) increased prosthetic limb COM push-off work, (3) decreased intact limb COM collision work, (4) decreased total COM work, and (5) reduced energetic cost of walking.
Section snippets
Participants
We examined seven traumatic unilateral transtibial amputees, 52.3 ± 12 years old, 1.85 ± 0.05 m in height, and weighed 80.9 ± 9.9 kg, who gave informed consent to participate in this IRB approved study. Participants were all male between 18 and 80 years old, wore a prosthesis for at least eight hours per day for a minimum of two years, could ambulate without upper-limb aides and had no history of injurious falls within the previous six months. They were considered moderately active community ambulators
Results
The CESR foot demonstrated 58% and 41% increases in prosthetic foot peak mechanical power output during push-off as compared to CONV (p < .001) and PRES (p = .001), respectively. CESR also demonstrated increased total work generation in push-off (61% more than CONV; 44% more than PRES; p < .001; Table 2B, Fig. 2A). The PRES foot also produced significantly greater push-off than the CONV foot (26% increase in power, p = .016; 27% increase in work, p = .004). Intact ankle peak power was 17% lower with CESR
Discussion
We compared transtibial amputees walking at a constant speed with each of three different prosthetic feet: a controlled energy storage and return (CESR) foot, a standard weight-matched conventional (CONV) foot and the participants’ own prescribed (PRES) foot using a within-subject, randomized study design. Our results revealed increased prosthetic limb push-off power and push-off work as well as increased prosthetic limb COM push-off work and reduced intact limb COM collision work with the CESR
Conclusions
In conclusion, transtibial amputees wearing the CESR foot demonstrated the ability to restore push-off energy on their prosthetic limb and reduce collision on their contra-lateral intact limb during constant speed ambulation; however, there was not a corresponding reduction in metabolic rate. The rate of release of the energy and its associated need for greater muscle work to control the energy release, or possibly inadequate adaptation time may have interfered with the amputees’ ability to use
Conflict of interest
Drs. Adamczyk and Collins are part-owners of Intelligent Prosthetic Systems, LLC, which was incorporated to perform research and development related to the CESR foot. None of the data presented here are proprietary. Foot prostheses based on this technology are under development, but none are commercially available.
Acknowledgments
This research was supported by the Department of Veterans Affairs, Rehabilitation Research and Development Service (A4372R). Other funding sources included the National Institutes of Health (HD055706), the Department of Defense (DR081177) and the National Science Foundation (Grant 0450646 and Graduate Student Research Fellowship). Statistical analyses were performed by Jane B. Shofer, MS. Prosthetic adjustments were performed by Wayne Biggs, CPO.
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- 1
Present address: Orthocare Innovations, Inc., Mountlake Terrace, WA, USA.
- 2
Present address: Department of Mechanical Engineering, Carnegie Mellon University, Pittsburgh, PA, USA.