Research and Clinical Selection of Foot-Ankle Systems

I t is important to realize that the “recommendation of ankle-foot systems for specific amputees” in today’s climate of evidence-based medicine would require that there is scientific evidence (a double-blind, placebo-controlled trial, using well-established and validated outcome measures) that shows enhanced function when a given component is provided compared with other suitable components. There are no studies that have been done that would meet this standard. This is supported by a systematic review of the literature between 1966 and 2001 by van der Linde et al. Of the reviewed studies, only one achieved a methodological level of A, and only 15 achieved a methodological rating of B. The majority of these studies addressed outcome variables of metabolic oxygen consumption, stride kinematics, ground reaction forces, or more sophisticated joint moment and joint power output characteristics. These studies generally showed few significant differences between feet. Three B-level studies did show an increase in self-selected walking speed with different energy-storing feet compared with the solid ankle cushioned heel (SACH) foot. Additional studies showed that the increase in walking speed was accomplished by a greater stride length and reduced cadence. In addition to kinematic measures, three of nine B-level studies showed a reduction in metabolic oxygen consumption with the Flex or the Re-Flex VSP compared with the SACH foot. Hafner et al. suggest that one of the important factors that have limited the achievement of statistical significance in these biomechanical and metabolic studies is the small sample sizes. This review compiled all the results from multiple studies and showed that there may be some important trends that can be inferred even though each individual study was not able to show significance. The graphic display of the cumulative data from multiple studies is very illustrative of this feature. Rietman et al. reviewed the literature between the years 1990 and 2000 related to “instrumented gait analysis” after amputation. This review concluded that gait analysis provides insight at the level of impairment but does not give insights at the level of disability or functional impairment. The authors conclude that gait analysis will continue to be of value in assessing the fundamental biomechanics of new prosthetic components, but further assessment of subjective perception and function in day to day functional tasks will be important. A fundamental question needs to be asked at this point. Even if all of these studies showed “improvement” in an isolated outcome variable such as self selected, stride length, ground reaction forces, or metabolic oxygen consumption, would that have been adequate evidence to “recommend their use in specific amputees”? From a theoretical perspective the answer would be no. What these studies would have demonstrated in a defined population, tested under specific laboratory conditions, was that there was a beneficial effect. This does not mean that there would have been any perceived or quantifiable beneficial effect in real-world use. The two relevant issues here are 1) Is the statistical difference of adequate magnitude to be clinically relevant? , and 2) Are the significant findings in the laboratory relevant to real world mobility? Hofstad et al. use the term “ecological validity” from Mulder. An example of the first issue is that a drug may cause a statistically significant 10% reduction in cholesterol but have no effect on the development of clinical atherosclerosis. An example of the second issue is that the metabolic costs may be reduced while walking in linear constant speed ambulation on a linoleum floor, but these conditions are rarely seen in day-to-day ambulation, and that walking in real-world conditions with stopping, starting, inclines, and stairs may in fact result in an increased metabolic oxygen consumption and an adverse effect on functional mobility. These questions should not be interpreted as a rejection for the need for fundamental biomechanical research. This research will be necessary to further understand the response of the amputee to changes in design and to assist in the development of novel prosthetic designs. Along with laboratory measurement, an additional approach used to quantify the effect of prosthetic feet is through subjective analysis. That is, amputees through a variety of mechanisms are asked to provide their subjective perceptions or define, in a quantifiable way, their subjective impressions in various domains. Hafner et al. have reviewed the literature in this regard. Unfortunately, few studies have met adequate quality to be interpreted as to their relevance. In the systematic literature review of van der Linde et al., only one level-A study and two level-B studies were acceptable. One showed no particular benefit of energy-storing feet over conventional feet and the other two showed some benefit of the Flex-Foot over the SACH foot; however, these studies were not conducted in a double-blind fashion. Blinding of subjects and investigators is clearly an essential part of studies that include a subjective evaluation.