Summary and Conclusions From the Academy's Eighth State-of-the-Science Conference, on the Biomechanics of Ambulation After Partial Foot Amputation

Jack E. Uellendahl, CPO,
Elaine N. Uellendahl, CP

It ain't what you don't know that gets you into trouble. It's what you know for sure that just ain't so.

—Mark Twain

Partial foot amputation (PFA) is a relatively common sequel to advanced diabetes and vascular insufficiency. More than 80,000 amputations are performed each year, with approximately one half of those being partial foot amputations. Although a broad array of orthotic and prosthetic devices has been designed for use by persons with PFA, their functional characteristics and benefits have generally not been quantitatively evaluated. Prostheses for this population vary from extremely rigid devices extending to the knee joint to flexible elastomeric ankle-height "boots" and "slippers" to simple toe fillers. The biomechanical differences between the wide array of prosthetic, orthotic, and pedorthic interventions used for this population have not been fully elucidated.

The purpose of this State-of-the-Science Conference (SSC) was to review the scientific literature regarding the biomechanical function during level ground walking of persons with PFA to establish what is known, what is believed to be true, and what needs to be known to optimize ambulation for these patients.

A multidisciplinary and multinational panel of experts convened in Chicago, Illinois, on March 3–4, 2007, to address this issue. Despite the focus of this conference, it was recognized by the participants that biomechanical analyses of devices used for ambulation with PFAs are only one aspect of prosthetic/orthotic prescription. Factors affecting protection of fragile skin, prosthesis comfort, and aesthetic value are also of critical importance when selecting the most appropriate prosthetic prescription.

To better understand the existing knowledge base and to identify areas of future research, four key questions were asked of the participants:

What do we know about the biomechanics of ambulation after PFA that has been validated by controlled studies, including meta-analyses or systematic reviews?
What do case series, retrospective reviews, or similar reports without controls suggest about ambulation after PFA?
Can a generic classification method, based on the biomechanical effect on ambulation, be developed for the plethora of orthoses and prostheses commonly prescribed for this population?
What are the major research priorities regarding the biomechanics of ambulation after PFA?

EXECUTIVE SUMMARY

This conference attempted to identify future research priorities, resulting in several recommendations. The systematic literature review provided the rationale for these recommendations, whereas the outcome statements included in the review illustrate specific priority areas for further research.

Questions 1 and 2 were the primary focus of the systematic literature review performed by Dillon et al.¹, although to some extent, the literature review helped assess all four key questions. The review demonstrated that there was a high level of evidence that PFA affected the biomechanics of gait, but there was little evidence to support a deeper understanding of the mechanics of gait or the influence of prosthetic and orthotic intervention. The additional presentations and discussions contributed by the other participants provided alternate views, discipline-specific insights, and an opportunity to discuss and debate insights regarding prosthetic/orthotic management of PFA so that a true consensus regarding the biomechanics of ambulation after PFA could be reached.

The vast majority of the published literature on PFA gait is observational in nature, whereby authors are trying to ascertain differences in PFA gait from that of able-bodied people. This is typically the starting point for research. Based on the modified National Institutes of Health (NIH) research model outlined in Table 4 of the systematic literature review¹, participants agreed that there remains a substantial need to establish foundation knowledge through further welldesigned observational studies. For example, observational studies may be used to develop a better understanding of the effect of level of amputation (and device) on temporospatial gait variables in cohesive groups of PFAs. Outcome statements listed in Tables 6 to 12 of the systematic literature review¹ with low or insufficient confidence illustrate the need for further observational studies to develop foundation knowledge in those specific areas. At present, not enough is known about the details of the mechanics of gait in PFAs.

Investigations of efficacy are needed to develop the next level of knowledge, that is, a better understanding of the effect of orthotic, prosthetic, and pedorthic interventions on ambulation after PFA. For example, experimental studies may be used to explore the effect of different prosthetic and orthotic interventions on excursion of the center of pressure. Outcome statements identified in the systematic review with a moderate level of confidence can be considered a priority for Phase I efficacy investigations. This will set the stage for future experimental studies.

Participants agreed that there was both a need to continue development of foundation knowledge and to develop investigations into the effect of different devices and different levels of amputation on PFA gait. Participants therefore recommended that the effect of different prosthetic and orthotic interventions (e.g., shoe/device interaction) and the effect of different amputation levels on gait should be studied with respect to the following aspects: skin pressures, kinematics, kinetics, energy expenditure, center of pressure, temporalspatial, and roll-over shape.

To carry out these studies effectively, a range of methodological issues endemic in the current body of literature needs to be addressed by future investigations, including:

Appropriate control group matching (for effects of systemic disease),
Heterogeneous amputee samples (e.g., age, time since amputation, device used, level of amputation, contralateral involvement),
Accommodation to device, randomization, training, and washout period,
Complete description of the interventional device (e.g., photos, materials specified, components, trim lines), and
Adequate reporting of results (post-hoc analysis, complete descriptive statistics).

Another major methodological issue raised in the systematic literature review that requires additional investigation was that of marker placement and the use of commercially available kinematic models. It was noted that with respect to gait analyses of PFA, there exist basic problems with accurately measuring motion about the foot and ankle because of loss of anatomical landmarks, obscuring of the required landmarks by devices or footwear, and relative motion between the residual limb, devices, and footwear. Many authors did not adequately report where markers were located, which models were used, or how marker placement was determined given the absence of particular anatomical landmarks. This hampers the reader's ability to understand and interpret the results and raises concerns regarding the validity of the measurements.

The long-term goal is to move toward methodologically strong, well-rationalized experiments and studies of efficacy. Researchers should be encouraged to develop standardized protocols that can be used in multicenter investigations to increase the available subject pool of subjects or to facilitate subsequent meta-analyses.

With specific regard to question 3, the participants concluded that a generic classification method based on the biomechanics of gait could not be developed because the majority of investigations currently available are focused on developing a basic understanding of differences in PFA gait from that of able-bodied adults using observational approaches. Observational studies do not allow the effects of different interventions to be quantified and understood in a systematic manner. Experimental studies provide a more appropriate methodology for understanding the effects of different devices on gait, and although several of these studies were available within the literature, they often were methodologically flawed or focused on isolated devices or levels of amputation, with limited generalizability. As such, there is insufficient experimental research of good quality to provide a mechanical basis for prescription of prosthetic and orthotic devices.

This conference illustrated that our understanding of the biomechanics of ambulation with a variety of PFA devices remains incomplete. Long-term, real-world efficacy studies of the plethora of devices used for the management of various partial foot amputation levels might facilitate development of a classification system in the future. The participants emphasized that biomechanics is only one consideration in clinical decision making and noted that other factors, such as patient preference, protection of insensate or fragile skin, and medical issues, must be considered in the prescription process and should be reflected in any classification system.

Once a stronger evidence base has been developed from both observational and experimental studies, clinicians and/or researchers can work toward identifying critical design features of prosthetic and orthotic interventions. This information will then provide objective evidence that can be used in the prescription of prosthetic, orthotic, and pedorthic interventions.

Correspondence to: Jack E. Uellendahl, Hanger Prosthetics and Orthotics, 4445 North 7th St, South Bldg, Phoenix, AZ 85014; e-mail:

JACK E. UELLENDAHL, CPO, is a prosthetics clinical specialist with Hanger Prosthetics and Orthotics in Phoenix, Arizona.

ELAINE N. UELLENDAHL, CP, is an independent prosthetics consultant in Scottsdale, Arizona.

References:

Dillon MP, Fatone S, Hodge MC. Biomechanics of ambulation after partial foot amputation: A systematic literature review. J Prosthet Orthot 2007;19:(8 Proceedings):P2–P61.