Secondary Logo

Journal Logo

Clinical Perspectives

Biomechanics of Ambulation Following Partial Foot Amputation: A Prosthetic Perspective

Berke, Gary M. MS, CP, FAAOP; Rheinstein, John CP, FAAOP; Michael, John W. MEd, L/CPO, FISPO, FAAOP; Stark, Gerald E. Jr CP, FAAOP

Author Information
JPO Journal of Prosthetics and Orthotics: July 2007 - Volume 19 - Issue 8 - p P85-P88
doi: 10.1097/JPO.0b013e3180d09e5d
  • Free

Abstract

This conference was convened to examine the available scientific evidence about the biomechanics of ambulation following partial foot amputation (PFA). The ultimate goal of the Academy's State-of-the-Science conferences is to document a body of scientific knowledge to support evidence-based practice (EBP) in the field of orthotics and prosthetics (O&P) that will lead to measurable standards of care and optimal patient outcomes. As the paper by Dillon et al.1 in these Proceedings illustrates, the process of establishing foundational scientific knowledge in O&P is still in its infancy. Nonetheless, their structured review provides useful information on the biomechanics of ambulation with PFA that can be immediately incorporated into clinical practice.

As clinicians, we have three primary responsibilities in the implementation of EBP. First, we must become knowledgeable consumers of the literature, keeping abreast of the latest relevant information. Second, we must develop the necessary skills to critically evaluate the available evidence and determine its clinical significance. Finally, we must integrate the significant information with our clinical expertise to make sound treatment decisions for each specific patient.

Because the current body of rehabilitation evidence is limited, many important clinical questions remain unanswered, and practitioners must often rely primarily upon their training and experience when making recommendations. Input from clinicians identifying critical issues is required to help prioritize future research directions. The future research topics reported elsewhere in these Proceedings reflect the broad consensus among those clinicians and scientists in attendance at this meeting.

This conference represents one step toward the development of a body of evidence sufficient to assist in the selection of one specific device design for an individual patient compared to alternatives. The comments that follow reflect the understanding that although expert consensus is often the best available evidence in O&P, the growing body of scientific information is directly relevant to patient management and can be readily incorporated into daily practice.

PROSTHETIC, ORTHOTIC, AND PEDORTHIC MANAGEMENT OF PARTIAL FOOT AMPUTATION

PFA presents a variety of unique clinical challenges, in large part because this general term encompasses a variety of distinctly different amputation levels that include toe amputations; ray resections; metatarsal phalangeal disarticulation; transmetatarsal amputation; tarsometatarsal or Lisfranc amputation; and intertarsal or Chopart amputation. Amputations intermediate to these named levels, combined with variations in surgical technique, add to the diversity of clinical presentations. A wide range of prosthetic, orthotic, and pedorthic interventions to manage the different residual limbs resulting from PFA have been described in published clinical reports.2–6

One of the major challenges when treating PFA is to provide an intervention that balances the often conflicting requirements of walking function, skin protection, user comfort, and cosmesis, despite residual foot shapes that are difficult to fit into conventional shoes. In addition, creating an appropriate prosthetic foot for these levels presents technical challenges. There is limited space between the distal end of the residuum and the shoe, but anything placed under the residuum creates a limb length inequality. Therefore, commercially available feet cannot be used, and customized solutions are required.

Biomechanical function during level ground walking, the topic of this conference, is always a consideration in managing these patients. However, it is not the sole criterion and may not be the most critical factor for a particular patient. Comfort and skin protection are frequently more important clinical goals for the severely debilitated patient, particularly in the presence of neuropathy, peripheral vascular disease, or a history of skin ulceration.

From a clinical perspective, interventions following PFA can be conveniently divided into high-profile devices that extend up onto the tibia and low-profile designs that terminate inferior to the malleoli. Prostheses per se are not the only option: Many devices for PFA incorporate orthotic principles as well. One high-profile example of such a hybrid approach would be the use of a modified ankle-foot orthosis (AFO) combined with a prosthetic toe filler.7 High-profile designs are often recommended in an effort to provide additional skin protection or improve suspension compared to alternatives.8

Low-profile designs are generally contained within the confines of the shoe; slipper-style variants are typical.9 A number of pedorthic interventions, including accommodative inlays or shoe modifications such as a rocker sole, are also commonly provided to this population.10–12 Most patients want the lightest and least conspicuous device possible, so low-profile designs are generally preferable to bulkier and less cosmetic alternatives. The Swedish text Partial Foot Amputations illustrates a range of contemporary high- and low-profile approaches and common footwear modifications.13

It is important to note that a specific level of PFA does not necessarily imply a particular type of prosthetic or orthotic design will be optimal. Not all proximal amputations require a high-profile design, and not all distal levels can be managed with low-profile alternatives. As a consequence of limitations in the available scientific information, the specific device provided remains primarily a clinical judgment. In developing a prescription recommendation, the practitioner weighs a number of clinical and biomechanical factors that include the client's goals and abilities, the characteristics of the residual limb, and the functional performance provided by different materials and designs.

APPLICATION OF SCIENTIFIC EVIDENCE

It has been widely assumed that the biomechanical functions of the forefoot during walking could be replicated through the use of a variety of prosthetic, orthotic, and pedorthic interventions14 High-top shoes, rocker bottom soles, carbon plates with custom insoles, and other devices have been routinely provided in an effort to enhance forefoot function after PFA. Although these devices may provide other benefits, the structured review by Dillon et al.1 demonstrates that biomechanical function in late stance can be only partially restored.

Some of the reported findings about ankle power and progression of the center of pressure (CoP) are particularly interesting from a clinical perspective because, although they contradict intuitive assumptions, they are well articulated in the literature and had supporting evidence reported in the review by Dillon et al.1 Selected implications of this information are highlighted below to illustrate the potential impact of emerging evidence on clinical decision making.

KINETICS: ANKLE POWER

It appears from the evidence reviewed by Dillon et al.1 that ankle power generation during level ground walking is not significantly compromised in those levels of PFA that retain the metatarsal heads. If power generation has not been impaired, individuals with toe ablations should demonstrate a nearly normal gait with simple devices such as an accommodative foot orthosis incorporating a toe filler. In the special case of ray resections, where most but not all of the metatarsal heads remain, no studies about the generation of ankle power during walking were reported.

However, once the metatarsal heads have been amputated, the ability to generate ankle power during rollover seems to be irrevocably lost, regardless of the residual foot length. In the studies reviewed by Dillon et al.,1 power generation was virtually negligible for subjects with hindfoot (Chopart), midfoot (Lisfranc), and forefoot (transmetatarsal) amputations. This understanding has a number of prosthetic and surgical implications.

Some authors have suggested that inframalleolar prostheses, orthoses, and footwear modifications are desirable because they do not restrict residual range of motion (ROM) at the ankle.15,16 It seems logical to hypothesize that if the prosthesis or orthosis permitted plantar flexion, propulsion would automatically be enhanced. However, none of the low-profile interventions in the studies reviewed by Dillon et al.1 demonstrated any substantial improvement in ankle power generation during late stance.

CENTER OF PRESSURE

A corollary hypothesis is that the person with PFA using a low-profile prosthesis would walk with a more normal rollover than when walking without a prosthesis. Investigation of the progression of the CoP in gait laboratory studies reviewed by Dillon et al.1 show clearly that this is not the case. With the low-profile devices studied, even when a rigid forefoot or carbon fiber plate was provided, the progression of the CoP did not extend beyond the end of the amputated segment until most of the body weight had been transferred to the opposite leg. This premature weight shift means that these low-profile devices were unable to restore effective forefoot length.

Some studies of the vertical ground reaction force have demonstrated increased magnitude of force on the contralateral limb during loading response when normal progression of the CoP has been lost.17 This raises concerns that the “drop-off effect” during ipsilateral late stance phase associated with low-profile devices might also result in increased loading on the contralateral foot.

The realization that it is not possible to restore ankle power once it has been surgically compromised, combined with the understanding that low-profile devices have little effect on progression of the CoP, places increased emphasis on other clinical considerations that are not gait related. Patient acceptance is always of primary importance, so designs that are lightweight, easy to maintain, unobtrusive, and comfortable may be preferred, despite the persistence of these gait deficits.

RESTORING EFFECTIVE FOREFOOT LENGTH

Studies reviewed by Dillon et al.1 suggest that only the high-profile designs that control dorsiflexion and have a relatively stiff forefoot will permit the amputee to walk such that the CoP extends beyond the end of the residuum under loading. A solid ankle bivalve (“clamshell”) prosthesis that immobilizes the ankle is one approach that has been shown to enable the amputee to roll over the anterior lever arm of the foot to produce a more normal progression of the CoP.18

This improvement in passive rollover is presumably facilitated by the extended contact with the tibia that is inherent in many high-profile designs. Trim lines that extend well proximal on the tibia provide sufficient leverage to keep peak pressures low enough for skin protection and patient comfort while rolling over the extended forefoot. Potential disadvantages of the solid ankle bivalve design—that a functioning ankle is immobilized and the approach is heavier, bulkier, and less cosmetic than alternatives—must be weighed against the improvement in gait mechanics.

It may be possible to create high-profile designs that permit some active ankle motion while still restoring an effective anterior lever arm. For example, the silicone partial foot prosthesis attached to a jointed ankle-foot orthosis (AFO) illustrated on the cover of these Proceedings allows plantarflexion during loading response, while the integrated dorsiflexion stops enable the patient to load the forefoot effectively during rollover.12 Recently, Wilson and Dillon19 published data showing that a modified carbon fiber AFO enabled a transmetatarsal amputee to walk with a relatively more normalized progression of the CoP without eliminating ankle motion.

To effectively restore missing forefoot length, it appears that specific high-profile devices are necessary. Low-profile prostheses and orthoses seem to have no impact on the movement of the CoP in late stance and thus can be considered to be biomechanically accommodative interventions that will not have the potential to affect step length.

CLINICAL ASSESSMENT

Restoration of the biomechanics of level ground walking is not the sole criterion for provision of a partial foot prosthesis. As Sage20 emphasizes in his article within these Proceedings, protecting the forefoot remnant from excessive pressures may be more important clinically for many amputees, particularly those with an insensate or an at-risk remnant foot. Standing balance is another important goal for many patients, particularly for those with limited ambulation capacity. Cosmesis and light weight are also significant clinical considerations for most patients.

A thorough evaluation of each patient's physical and mental capabilities, environmental conditions, and ADL goals remains essential when developing a sound recommendation for a specific orthotic, prosthetic, or pedorthic intervention for this challenging and diverse group of amputees. Although the best available evidence suggests that only a high-profile device that restricts ankle dorsiflexion is capable of partially restoring the missing anterior lever arm, patients frequently reject such bulky designs. Clinicians must carefully weigh the advantages and limitations of each approach to determine the best recommendation to meet the individual needs and goals for each patient.

EVIDENCE-BASED PRACTICE

Incorporation of the latest scientific evidence into the clinical decision-making process is the hallmark of EBP. This conference makes a valuable contribution to patient care by clarifying certain aspects of the biomechanical performance of devices commonly used in the management of PFA.

These Proceedings enable the clinician to advise the clinic team that, although low-profile approaches cannot be expected to improve the anterior progression of the CoP during walking, they may offer other functional advantages that are of more clinical importance to a specific patient. Restoration of effective forefoot length appears to require the provision of certain high-profile designs that enable the amputee to passively roll over the prosthetic forefoot.

The evidence from this structured review is consistent with the clinical viewpoint that the optimal intervention cannot be determined based solely on the level of partial foot amputation. Selection of the best configuration for a specific patient remains a clinical judgment, informed by experience, training, and the best available scientific evidence.

ACKNOWLEDGMENTS

Mr. Rheinstein thanks Lew Schon, MD, for his guidance and dedication to advancing the care of amputees. Mr. Stark thanks Tom Karolewski, CP, FAAOP, and Northwestern University's Prosthetic-Orthotic Center for their clinical advisement.

REFERENCES

1. 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.
2. Rubinstein HJ, Sweeney GJ, Strong P, et al. A foot amputation orthosis-prosthesis. Inter-Clin Info Bull 1975;14:11–15.
3. Moore JW. Prostheses, orthoses, and shoes for partial foot amputees. Clin Podiatr Med Surg 1997;14:775–784.
4. Staros A, Peizer E. Orthopaedic shoes for bilateral partial foot amputations. Artif Limbs 1965;9:27–34.
5. Sobel E, Japour CJ, Giorgini RJ, et al. Use of prostheses and footwear in 110 inner-city partial-foot amputees. J Am Podiatr Med Assoc 2001;91:34–49.
6. Lange LR. The Lange silicone partial foot prosthesis. J Prosthet Orthot 1991;4:56–61.
7. Stills ML. Partial foot prostheses/orthoses. Clin Prosthet Orthot 1988;12:14–18.
8. LaTorre R. The total contact partial foot prosthesis. Clin Prosthet Orthot 1988;12:29–32.
9. Fillauer K. A prosthesis for foot amputation near the tarsal-metatarsal junction. Orthot Prosthet 1976;30:9–11.
10. Brown D, Wertsch JJ, Harris GF, et al. Effect of rocker soles on plantar pressures., Arch Phys Med Rehabil 2004;85:81–86.
11. Potter JW, Sockwell JE. Custom-foamed toe filler for amputation of the forefoot. Orthot Prosthet 1974;28:57–60.
12. Philbin TM, Leyes M, Sferra JJ, Donley BG. Orthotic and prosthetic devices in partial foot amputations. Foot Ankle Clin 2001;6:215–28.
13. Söderberg B, Wykman A, Schaarschuch R, et al. Partial Foot Amputations. Helsingborg, Sweden: Swedish Orthopaedic Association–AB, 2001.
14. Condie DN. Biomechanical and prosthetic considerations. In: Murdock G, Wilson AB Jr. Amputation, Surgical Practice and Patient Management. Oxford, United Kingdom: Butterworth-Heinemann; 1996;104–107.
15. Parziale JR, Hahn K-AK. Functional considerations in partial foot amputation. Orthop Rev 1988;17:262–266.
16. Rubin G, Danisi MA. Functional Chopart prosthesis. Inter-Clin Info Bull 1972;11:3–5.
17. Burnfield JM, Boyd LA, Rao S, et al. The effect of partial foot amputation on sound limb loading forces during barefoot walking. Gait Posture 1998;7:178–179.
18. Dillon MP, Barker TM. Can partial foot prostheses effectively restore foot length? Prosthet Orthot Int 2006;30:17–23.
19. Wilson EJ, Dillon MP. Restoring centre of pressure excursion using a toeoff orthosis in a single partial foot amputee. Paper presented at the International Society of Prosthetics and Orthotics, Australian National Member Society, Sydney, Australia, November 2–5, 2005.
20. Sage RA. Biomechanics of ambulation after partial foot amputation: prevention and management of reulceration. J Prosthet Orthot 2007;19(8 Proceedings):P77–P79.
Keywords:

Chopart amputation; evidence-based practice; Lisfranc amputation; lower limb amputation; orthoses; partial foot; prostheses; toe amputation; transmetatarsal amputation

© 2007 American Academy of Orthotists & Prosthetists