Ankle Disarticulation and Variants: Prosthetic Management

Phillip M. Stevens MEd, CPO, FAAOP

David J. Baty CPO, LPO

David J. Baty or an immediate family member serves as a paid consultant to or is an employee of Össur. Neither Phillip M. Stevens nor any immediate family member has received anything of value from or has stock or stock options held in a commercial company or institution related directly or indirectly to the subject of this chapter.

This chapter is adapted from Kanas JL, Stevens PM: Ankle disarticulation and variants: Prosthetic management, in Krajbich JI, Pinzur MS, Potter BK, Stevens PM, eds: Atlas of Amputations and Limb Deficiencies: Surgical, Prosthetic, and Rehabilitation Principles, ed 4. American Academy of Orthopaedic Surgeons, 2016, pp 479-484.

ABSTRACT

Syme ankle disarticulation has been suggested as the most functional amputation level of the lower limb, yet it is increasingly rarely encountered in clinical practice. The procedure typically allows for a functional gait pattern because of the preservation of a long residual limb and good muscle strength in the hip and knee proximal to the amputation. However, prosthetic fittings can be challenging because of the long and bulbous shape of the residual limb, which can result in less than optimal cosmesis and limitations to options for prosthetic componentry and feet.

Introduction

An amputation through the ankle joint was originally described by Syme¹ in 1843 and has colloquially retained his name ever since. Although Syme’s initial surgical technique has undergone changes and refinements over time, it remains an ankle disarticulation in which the distal heel tissue is reattached to the limb to allow direct weight bearing through its distal end (Figure 1). Although an ankle disarticulation has been suggested by some as the most functional amputation level,² certified prosthetists in the United States report spending only 4% of their time working with patients who have undergone a Syme ankle disarticulation.³ These divergent observations are the result of the striking advantages and disadvantages associated with this amputation level. The inherent advantages include full distal weight bearing in most cases, a long lever arm with a large surface area for load distribution, anatomic suspension with innate rotational stability of the socket over the limb, and minimal disturbance to growth plates in pediatric applications. The disadvantages are the difficulty in creating a cosmetically acceptable prosthesis and the reduced space available for modern prosthetic foot options. The anticipated outcomes associated with an ankle disarticulation amputation along with its inherent advantages and disadvantages are reviewed. Variations in socket and suspension designs as well as component considerations are discussed.

Anticipated Outcomes

Ankle disarticulation may be indicated for several different adult patient populations including those with vascular compromise, diabetes mellitus with gangrenous tissue, severe Charcot foot arthropathy, nonhealing dysvascular ulcers, severe diabetic ulcers, trauma, crush injuries, severe frostbite, and malignancy.⁴^,⁵ Although recent literature has been silent with respect to the functional outcomes associated with this amputation level, legacy publications suggest that these outcomes will vary with the underlying etiology and overall health and well-being of the patient.

Siev-Ner et al⁵ reported on the results of ankle disarticulations in 70 patients. The procedure was performed in 51 of the patients because of diabetic vascular disease. A successful outcome was defined as one in which revision amputation was not needed in the first year postoperatively, and the patient successfully received a prosthesis and completed prosthetic gait training. Using these criteria, success rates of 94% were reported for the 19 patients without vascular disease and 49% for those with vascular disease. Further classification based on age in those with vascular disease showed the success rate was 68% for patients younger than 65 years, 31% for those 65 to 69 years, and 14% for those older than 70 years.

Yu et al⁴ reported on a cohort of individuals with ankle disarticulation of mixed etiology, including Charcot
arthropathy, osteomyelitis, crush injury, and elective amputation of severe clubfoot. Nine of 10 patients achieved ambulation with a prosthesis by 4 to 6 months after amputation, and 7 patients reported improved quality of life and return to activities of daily living.

FIGURE 1 Photograph of the limb of a patient after a right ankle disarticulation.

In a retrospective study of patients treated with a Syme ankle disarticulation, Pinzur et al⁶ evaluated 97 patients with diabetes mellitus with a mean age of 53 years and at least 2 years of follow-up. Of 82 patients whose wounds healed, 80 were able to use a prosthesis, a higher rate than that generally observed among patients with diabetes who have more proximal amputations. Of these, 50% were classified as household walkers and 50% as community walkers.

A relatively recent subsequent retrospective long-term analysis of 51 patients treated by the same primary author included 33 patients with diabetes mellitus and 18 patients with nonvascular etiologies.⁷ The average age at amputation for the first group was 62 years, whereas the average age of the second group was 38 years. Four of those patients with diabetes (12%) had eventually gone on to transtibial amputation because of wound failure or infection, compared with one patient (5.5%) among the cohort without diabetes. Half of the cohort with diabetes were deceased at the time of review, with an average of 4.6 years between their amputation and death. The long-term function and mobility of 11 patients who could be contacted were assessed. Although scores were higher for patients without diabetes, outcome scores were favorable for both cohorts.

Frykberg et al⁸ reported on a cohort of 26 patients who underwent a Syme ankle disarticulation. Before surgery, these patients had an infection and/or substantial peripheral arterial disease and 92% had diabetes. Even with prior recommendation for transtibial or transfemoral amputation in all patients and a high rate of postoperative complications, including dehiscence, recurrent osteomyelitis, infection, and pressure ulcers, 65% of the patients successfully attained initial ambulation with a prosthesis. However, several of the patients required more proximal amputations at a mean period of 28 weeks after the ankle disarticulation because of progressive sepsis or recurrent ulcers. Ultimately, 46% of the patients were functioning well with an ankle disarticulation prosthesis approximately 1 year postoperatively. The preoperative patient criteria were less strict than in other published standards and may have resulted in the comparatively high failure rate, but several patients who would have been excluded using stricter criteria went on to ambulate successfully with a prosthesis after ankle disarticulation.

Thus, the success of prosthetic ambulation after ankle disarticulation varies, depending on the causative etiology and other medical considerations. Patients with traumatic amputation appear to do quite well, whereas the success of amputees with vascular comorbidities is more varied.

Clinical Considerations

A few unique clinical considerations differentiate ankle disarticulation from the more common transtibial amputation. These include the defined benefits and drawbacks of the associated shape and length of the residual limb, the preservation of the distal heel pad with the associated ability to bear weight distally, and the cosmetic challenges associated with the disarticulation prosthesis.

Residual Limb Shape and Length

After ankle disarticulation, the residual limb is characterized by an often pronounced bulbous contour secondary to the shape of the distal tibia and fibula. In addition, the heel pad is spared from the ablated foot during surgery and reattached distal to the tibia and fibula. Proponents of ankle disarticulation cite several associated benefits of this characteristic limb shape and length. Because of the absence of any transected long bones, coupled with the preservation of the heel pad of the foot, the residual limb often has the potential to provide distal end bearing with increased proprioception following ankle disarticulation. In addition, by preserving the entire length of the tibia and fibula, one of the most important and unique advantages of ankle disarticulation is that it permits limited ambulation without a prosthesis, albeit with a considerable limb-length discrepancy. Although this limb-length discrepancy and the stability of the distal heel pad preclude ambulation over extended distances, limited direct end bearing can be useful for short-distance ambulation in the home (eg, for a nightly bathroom visit) or at a swimming pool.

In addition, the extended length of the residual limb after ankle disarticulation provides a long lever arm for
control of a prosthesis. When the limb can tolerate full distal weight bearing, the proximal trimlines of the prosthesis can be lowered relative to those used in transtibial applications. Anteriorly this trimline can be lowered to the tibial tubercle or lower. However, consideration needs to be given to the shape of the anterior proximal edge of the socket because the dynamic forces experienced in late stance will tend to load the anterior tibial crest.

When the position or stability of the distal heel pad is compromised and distal weight bearing is poorly tolerated, a transtibial patellar tending brim can be used to help distribute the axial forces across the proximal aspects of the limb as in transtibial applications. In addition, the extended length of the residual limb provides a large surface area over which these proximal weight-bearing forces can be distributed. The bulbous shape of the ankle disarticulation also provides the ability to self-suspend the prosthesis.

These benefits notwithstanding, several clear disadvantages are associated with the prosthetic management of a patient after an ankle disarticulation. The extended length of the residual limb can limit prosthetic component options. In an adult treated with ankle disarticulation, the available space is inadequate to fit a higher profile prosthetic foot capable of energy storage and return and shock absorption. Similarly, space is limited for modular components that can be used in more proximal limb prostheses for alignment adjustability. Finally, providing a cosmetically acceptable ankle disarticulation prosthesis can be challenging, especially for an individual with a more bulbous residual limb.

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