Nearly all lower limb prostheses for levels through the anatomical ankle or higher include a prosthetic foot and ankle system. This may be as uncomplicated as a solid ankle cushioned heel foot bolted to a rigid laminated ankle block, or as complex as a foot that combines multiaxial features with carbon plates, adjustable heel stiffness, and modular connectors. The array of choices increases as new feet are introduced. Although such diversity is generally an advantage, selecting the best foot and ankle to match the patient’s needs and goals can be a challenge. As foot-ankle technology has advanced, so have methods and means to understand how prosthetic feet work or compare with each other, and what impact they may have on a user’s function. This knowledge base comprises the current state of the art. Patients, clinicians and third-party payers receive information about feet through various sources including advertising, manufacturer’s specifications, anecdotal clinical experience, and published evidence-based reports. Recently a group of engineers, biomechanists, prosthetists, therapists, and physicians, all involved in various aspects of developing, fitting, and studying prosthetic feet, spent nearly 3 days reviewing the literature and attempting to summarize the current state of the science of prosthetic feet and ankles.
This State-of-the-Science Conference (SSC) on prosthetic feet and ankle mechanisms was convened April 14–16, 2005, in Dallas, at Texas Scottish Rite Hospital for Children. The SSC is an activity in evidence-based health technology assessment and transfer conducted by the American Academy of Orthotists and Prosthetists. Under this program, the Academy organizes major conferences to produce statements on the current state of the science and identification of potential research priorities on important topics related to the provision of orthotic and prosthetic (O&P) care.
An SSC is designed to provide a systematic review of literature and ranking of evidence on a conference topic. The purpose is to evaluate the available scientific information on an aspect of O&P care and develop statements that advance understanding of the issues in question that will be useful to health professionals and the public. It may also serve as a mechanism to document clinical belief systems in O&P care, based on what is understood through sound research or from expert opinion. The end goal of an SSC is to publish a document that identifies and ranks the available evidence and defines the current status of patient care, to develop consensus on controversial issues where possible, and to identify research priorities.
The SSC on Prosthetic Foot-Ankle Mechanisms was called to examine the body of scientific evidence that supports the clinical prescription and use of prosthetic foot and ankle mechanisms. It is generally understood that components such as torque and shock absorbers can be added to alter the function of many feet. For purposes of simplicity and focus, such separate components were excluded from this review. Studies regarding foot-ankle components that included vertical shock or torsion absorption as part of their fundamental mechanical design were included.
An SSC is developed around key questions posed to the panelists. Those questions identified as relevant to the prescription and use of prosthetic foot-ankle mechanisms were:
What scientific methods have been used to determine the functional performance of prosthetic feet and ankle systems in current use?
What is the correlation between the available scientific measurements and the clinical methods used to recommend ankle-foot systems for specific amputees?
What is the correlation between prosthetic foot-ankle systems and prosthetic outcomes (e.g., performance, patient acceptance, durability)?
In light of the literature review and the panel’s discussion, what are the primary future research priorities?
Because it is the goal of the SSC to examine, debate, and answer these questions, panelists were asked to review the literature applicable to one or more of these questions and to write a paper and present their perspectives to the group. Throughout the process, all participants were asked to consider the relevance and validity of the following key areas:
- Time-distance parameters as a measure of prosthetic performance
- O2 consumption/energy consumption studies
- Comparisons to normal gait and normal foot-ankle function
- Comparisons to other prosthetic feet
- Patient preference studies
- Other methods used to evaluate or compare foot-ankle function
Although some discussions were lively and there were understandably areas of controversy, ultimately there was general agreement on the responses summarized herein. On those occasions when the group seemed unlikely to reach consensus, those areas of controversy were identified for future research.
Several articles in this supplement include descriptions of normal foot function; therefore, some repetition was unavoidable. Because each author provides a different perspective — prosthetist, engineer, biomechanist, therapist, etc. — each was thought to be distinct and valuable on its own merits.
The Review of the Literature provides an excellent contextual “map” of the review process that assisted participants in developing their papers and in answering the key questions as a group. The discussion on Terminology introduces some key differences and similarities in how members of a multidisciplinary team may perceive and discuss prosthetic foot function, gait and related biomechanics. Responses to each key question are summarized, and discussions on each topic are presented.
As expected, this was a multidisciplinary group, so the final product reflects diverse perspectives and areas of common ground. The entire project stimulated a great deal of discussion regarding future research and development of prosthetic foot-ankle mechanisms, and how such research can be improved and made more relevant.