Partial Foot Amputation: Prosthetic Management

Michael P. Dillon PhD, BPO(Hons)

Stefania Fatone PhD, BPO(Hons)

Dr. Dillon or an immediate family member serves as a board member, owner, officer, or committee member of the International Society for Prosthetics and Orthotics. Dr. Fatone or an immediate family member serves as a board member, owner, officer, or committee member of the American Academy of Orthotists and Prosthetists, the American Orthotic and Prosthetic Association, and the International Society for Prosthetics and Orthotics.

ABSTRACT

Partial foot amputation is the most common amputation surgery and typically affects the toe(s) and/or metatarsals. Partial foot amputation is often performed in people with advanced peripheral arterial disease when extensive efforts to heal recalcitrant wounds have been unsuccessful. Although many people perceive that partial foot amputation will resolve long-standing issues with poor wound healing, a large proportion of people will experience serious complications such as infection, wound breakdown, or reamputation on the same limb in the months and years that follow. Although there is good evidence describing the surgical outcomes following partial foot amputation, research focused on other outcomes such as community mobility, health-related quality of life, or psychosocial outcomes is limited. Similarly, there is little evidence comparing the effectiveness of different types of prosthetic and orthotic interventions, which makes it difficult to determine which interventions most reduce the risk of complications and reamputation. An introduction to partial foot amputation and common prosthetic and orthotic interventions is provided, and current knowledge about the effect of different prosthetic and orthotic interventions is summarized. The clinical and research implications are also discussed with a view to addressing the wide range of challenges faced by those living with partial foot amputation.

Introduction

Partial foot amputation (PFA) is perhaps the most common amputation surgery with an annual incidence rate of 4.0 per 100,000 general population (95% confidence interval 3.8 to 4.2).¹ However, significant complexity belies such simple statistics. For example, the incidence rate is about fourfold higher in studies that only include people older than 30 years, which might better describe the population at risk.¹ Similarly, the incidence rate is about 25 times higher in cohorts with diabetes compared with those without.¹ Studies that exclude people with toe amputation or repeat amputations underestimate the incidence rate. These illustrative examples highlight how minor variations in the design of epidemiologic research can have a profound effect on the calculated incidence rate, which adds significantly to the challenge of accurately describing the number of amputation procedures each year.

Given these sorts of variations in the design of epidemiologic research, there is also uncertainty about whether the incidence rate of PFA has changed over time.¹ For example, many time-series investigations are too short to allow small changes in the annual incidence rate—typically less than 1% to 2% per annum—to become large enough to be statistically significant.¹ Similarly, studies of individual health services often have small participant numbers that make them susceptible to chance variations from year to year that tend to dwarf the small, cumulative, changes in the incidence rate over time.¹

Although there is some uncertainty about whether the incidence of PFA has changed over time, public health initiatives designed to curb the incidence of limb loss, such as early assessment at specialist high-risk foot clinics or better management of diabetes at a community level,²^,³^,⁴^,⁵^,⁶ may mean that the number of people at risk because of diabetes⁷^,⁸ are presenting with less severe vascular disease that may help avoid the need for amputation surgery in their lifetime.

About three-quarters of all PFAs affect one or more toes, with comparatively few ray resections, transmetatarsal, tarsometatarsal (Lisfranc), or transtarsal (Chopart) amputations⁹^,¹⁰^,¹¹^,¹² (Figure 1). The proportion of PFA affecting the toes may seem unusually high to prosthetists/orthotists given that they tend to only see people with more proximal amputation. A large proportion of people with amputation of the toe(s) may receive follow-up care through high-risk foot clinics rather than prosthetic and orthotic centers.

FIGURE 1 Schematic representation of common levels of partial foot amputation. A, Amputation of the fourth and fifth toes. B, Resection of the third, fourth, and fifth metatarsals and toes (rays). C, Disarticulation at the metatarsophalangeal joint. D, Transmetarsal amputation. E, Tarsometatarsal (Lisfranc) amputation. F, Transtarsal (Chopart) amputation (sometimes also referred to as midtarsal).

Over recent years, a greater appreciation of the complications experienced by people living with PFA has developed. Between 30% and 50% of people with PFA experience complications such as dehiscence, ulceration, and wound failure.¹³ To some extent, these complications may be attributable to the complexities of predicting which amputation levels will heal best; particularly in people with serious vascular compromise and complex comorbidities (eg, end-stage renal disease, hypertension, diabetes).¹³^,¹⁴ There are longer term challenges: managing progressive equinovarus contractures¹⁵^,¹⁶^,¹⁷^,¹⁸ and moderating higher forefoot plantar pressures relative to the contralateral limb or appropriately matched control subjects.¹⁹^,²⁰^,²¹ These sorts of complications likely contribute to the fact that half of all initial PFA require secondary amputation on the same limb within 5 years; a rate not appreciably different between levels of PFA.¹³ These rates of complications are often not markedly better in people without diabetes, making it difficult to conclude that the high rate of complications are merely a reflection of advanced systemic disease.¹³

Recognizing these challenges, researchers have recently developed shared decision-making resources to help patients engage in more meaningful conversations about amputation surgery,²²^,²³ as well as decision support tools that allow health professionals to accurately predict the likely success of different amputation procedures based on individualized patient demographic, laboratory, and health-related factors.¹⁴^,²⁴^,²⁵ Common to these resources is the desire to help facilitate more meaningful communication between patients and health care clinicians, as well as provide accurate information about the likely outcomes and risks. In this way, patients can make more informed decisions about amputation surgery and exercise greater control over their health care.²²^,²³

For those living with PFA, a wide variety of prostheses and orthoses are provided to help minimize complications and restore premorbid function,²⁶^,²⁷^,²⁸ thus facilitating self-care and participation in activities that bring joy and meaning to life. The types of devices provided to meet these treatment goals have changed little over time: toe fillers, insoles, silicone cosmetic prostheses, ankle-foot orthoses (AFOs), and above-ankle prostheses are still commonly used.

Although the types of devices may have changed little over time, emerging research challenges long-held views about how effectively current prosthetic and orthotic interventions can meet the needs of people with PFA.²⁹ For example, although prostheses and orthoses can be designed to restore the effective foot length,³⁰^,³¹ it is unclear whether normalizing gait is important to return people to their premorbid level of community mobility. There is little knowledge about which interventions significantly reduce the rates of complications and reamputation. Similarly, it is uncertain whether different interventions affect health-related quality of life (HR-QoL) or facilitate participation in activities that bring joy and meaning to life. These emerging insights continue to guide efforts to better understand how prosthetic and orthotic interventions can be of benefit to people living with PFA.

Current knowledge about PFA and the effect of prosthetic and orthotic intervention are summarised in this chapter. The following sections briefly describe common categories of prostheses and orthoses currently provided to meet the needs of people living with PFA. The emerging evidence, and implications for clinical practice and research, are also discussed.

Interventions

A wide variety of custom prosthetic, orthotic, and footwear interventions are provided to people living with PFA.²⁶^,²⁷^,²⁸^,³²^,³³ These interventions are often categorized as below-ankle or above-ankle depending on whether the device crosses the ankle joint.¹⁶^,²⁷ Common below-ankle interventions include toe fillers, insoles, and silicone cosmetic prostheses; common above-ankle interventions include AFOs and above-ankle prostheses. Some investigators have recently tried to incorporate elements of the two by embedding supramalleolar or short AFOs inside silicone prostheses.³⁴^,³⁵

These interventions may fulfil several different treatment goals. For example, devices may be provided to minimize interface pressures on the distal end of the residuum and prevent equinovarus contracture with the expectation that they reduce the risk of ulceration and skin breakdown that often leads to more proximal
amputation.²⁷^,³²^,³⁶^,³⁷ Devices may be provided to make standing and walking more comfortable or restore premorbid mobility.²⁶^,²⁷^,³²^,³⁸^,³⁹^,⁴⁰^,⁴¹ Other devices provide a high degree of cosmetic restoration.²⁶^,²⁷^,³² Devices may also be used in combination to achieve multiple treatment goals. For example, a carbon-fiber, anterior shell AFO might be used with an insole and toe filler (Figure 2) to restore the effective foot length and normalize gait, as well as distribute pressure away from the distal end of the residuum to provide protection and improve comfort during standing and walking.

As a generalization, people with more proximal amputations tend to be provided with more substantial devices. A person with amputation disarticulating the metatarsophalangeal joints might be provided with an insole and/or toe filler (Figure 3). By comparison, someone with a Chopart (transtarsal) amputation might be provided with an above-ankle prosthesis that encloses the residuum and leg in a solid plastic shell (Figure 4). Those with amputations through the midfoot (eg, transmetatarsal amputation or ray resections) tend to be provided with a much wider variety of interventions varying from insoles, silicone cosmetic prostheses, and/or AFOs.

FIGURE 2 Photograph of a Blue Rocker ToeOff ankle-foot orthoses combined with an ethylene-vinyl acetate insole. (Courtesy of Prosthetics and Orthotics Department, Royal Melbourne Hospital, Melbourne, Australia.)

The types of interventions provided to people with PFA vary across countries and health jurisdictions depending on the stipulations of funding bodies, the professional disciplines involved in providing care, and the expertise/experience of treating clinicians. In Australia, for example, pedorthic approaches (eg, custom or customized footwear) seem to be less common than in parts of the United States, Japan, and many European countries where the formal training and expertise of pedorthotists are better recognized in healthcare practice.

FIGURE 3 Photograph of an insole and toe filler for a transmetatarsal residuum. Ethylene-vinyl acetate sole supporting the hindfoot and arch. Poron, an open-cell polyurethane foam, has been used to protect the sensitive distal/inferior end of the residuum. The toe filler is made from Plastazote, an expanded low-density polyethylene closed-cell foam. (Courtesy of Prosthetics and Orthotics Department, Royal Melbourne Hospital, Melbourne, Australia.)

FIGURE 4 Photograph of a bivalved above-ankle prosthesis for a Chopart residuum (sometimes referred to as a clamshell prosthesis). The laminated socket is made of a resin and glass-fiber composite and includes a closed-cell polyethylene foam liner. (Courtesy of Prosthetics and Orthotics Department, Royal Melbourne Hospital, Melbourne, Australia.)

It is beyond the scope of this chapter to comprehensively describe the wide variety of devices provided to people living with PFA. As such, the following subsections aim to characterize the most common categories of prosthetic and orthotic interventions in terms of their application to different amputation levels, design variations, and treatment objectives.

Toe Fillers and Insoles

Toe fillers and insoles (Figure 3) are common interventions for people with distal forefoot amputations such as amputation of the toe(s), disarticulation at the metatarsophalangeal joints, or ray resections. However, it is not uncommon for people with transmetatarsal amputation to also be provided with toe fillers and insoles.

Toe fillers are used to fill the cavity in normal length footwear. They can be used alone or attached to an insole. Insoles serve as a bed for the remnant foot and can be designed with the intention to maintain the alignment of the residuum and redistribute pressure away from the sensitive distal end with a view to minimizing the likelihood of skin breakdown.⁴² Both toe fillers and insoles are designed to be worn as part of footwear. Given that they do not encompass the residuum, they rely on the shoe to maintain their position with respect to the remaining foot (ie, a form of suspension). Extra-depth footwear or low-top boots may be provided to accommodate the orthoses and provide adequate suspension.

Toe fillers and insoles are often made from closed-cell foams that resist compression and therefore thinning (eg, ethylene-vinyl acetate) but may incorporate materials with different mechanical properties based on
the defined treatment goals. For example, closed-cell polyethylene foam might be used under the heel and arch to correct foot alignment, whereas a low-density material might be used to protect the distal end of the residuum against shear forces (Figure 3). Some toe fillers incorporate vertical cuts through the dorsum, much like the Shape&Roll prosthetic foot,³⁰^,⁴³ with a view to reducing the stiffness of the filler and facilitating bending when rolling over the forefoot during walking. Some devices take the opposite approach and include a carbon-fiber foot plate to help prevent buckling of the orthoses across the distal end of the residuum when loaded. Unfortunately, the efficacy of these approaches has not been evidenced by research.

Silicone Cosmetic Prostheses

Silicone cosmetic prostheses (Figure 5) provide the most cosmetic restoration of the partially amputated foot given that it is possible to match the shape and alignment of the toes and nails, and skin color variations, to that of the contralateral limb. These devices are usually, but not exclusively, provided to people with amputation at or distal to the midfoot.

The design of the prosthesis depends on the remnant foot: a prosthesis for someone with transmetararsal amputation might take the form of a slipper socket that encompasses the entire residuum (Figure 5, A), whereas a prosthesis for someone with a lateral ray resection would require a distal opening for the medial rays/toes to protrude through the end of the prosthesis (Figure 5, B).

Silicone prostheses are made to intimately fit the residuum, requiring water-based lubricant and a shoehorn for donning. This intimacy of fit provides suction suspension enabling the prosthesis to be worn with flip flops or sandals. Although silicone prostheses may be worn without footwear, providers usually recommend wearing footwear outdoors to prolong the life of the prosthesis.

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