Ankle Disarticulation and Variants: Surgical Management

LTC Tobin Thomas Eckel MD, FAAOS

Scott B. Shawen MD

Dr. Shawen or an immediate family member has received royalties from CrossRoads and Medline and serves as a paid consultant to or is an employee of CrossRoads, KCI, Medline, Panther Orthopaedics, and Restore 3D/Kinos. Neither Dr. Eckel 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 Eckel TT, Chi BB, Shawen SB. Ankle disarticulation and variants: surgical management. In: Krajbich JI, Pinzur MS, Potter BK, Stevens PM, eds. Atlas of Amputations and Limb Deficiencies: Surgical, Prosthetic, and Rehabilitation Principles. 4th ed. American Academy of Orthopaedic Surgeons, 2016, pp 473-477.

ABSTRACT

Advancements in transtibial amputation techniques and prostheses have led to decreased use of ankle disarticulation. However, these distal amputations are still a viable option in select circumstances. They are most commonly used in diabetic infection, nonhealing ulcers, deformity, and trauma. Advantages include earlier weight bearing, decreased dependence on prosthetics, and decreased energy expenditure with ambulation. Common complications include delayed wound healing, infection, and heel pad migration.

Introduction

With recent advancements in transtibial prostheses and the concern for wound healing with more distal amputations, the ankle disarticulation has fallen somewhat out of favor, but still remains a viable option in select patients. The ankle disarticulation is commonly referred to as a Syme amputation, as James Syme is credited with first describing this amputation in 1843.¹^,² Transtibial amputations account for nearly 25% of all lower extremity amputations, whereas only 10% of all lower extremity amputations are performed about the foot and ankle.³

At the time Syme described his novel amputation, he stated the advantages of his described disarticulation were: “the risk of life will be smaller, that a more comfortable stump will be afforded, and that the limb will be more seemly and useful for progressive motion.”⁴ These claims remain largely unchallenged today. The mortality rate with ankle disarticulation has been reported as 33% at 5 years compared with 33% at 2 years with transtibial amputation.⁵ Some have attributed the decreased mortality to decreased blood loss and the ability to perform under regional anesthesia.⁶ This decreased mortality must be tempered by the high failure rate of ankle disarticulation, with revision rates ranging between 20% and 50%.⁷

The Syme amputation is considered to be more comfortable because the heel pad is preserved. The heel pad contains fat cells enclosed by dense fibrous septae, which allows for direct weight bearing. The preservation of the heel pad therefore affords end weight bearing without a prosthetic.¹^,³^,⁴^,⁵ Although the ability to bear direct weight without a prosthetic is a significant advantage, it is important to realize that the weight is absorbed by a single bony surface, compared with an entire foot that consists of a multitude of joints and surrounding musculature that is specialized to bear weight and adapt to uneven surfaces. For these reasons, weight bearing without a prosthetic is typically limited to very short distances.²^,⁸ Nonetheless, the ability to end weightbear and simplicity of prosthetic fitting can lead to decreased length of rehabilitation and negate the need for long-term inpatient care following amputation.⁹ Furthermore, the ability to end weightbear is very important when considering prosthetic design. The Syme amputation allows for sockets to function in suspension, whereas transtibial sockets bear weight by indirect load transfer, and thus with any volume changes in the residual limb, the socket would need to be revised to prevent any tissue breakdown.²

Last, Syme’s claim was “that the limb would be more seemly and useful for progressive motion.” Many would argue against an ankle disarticulation being a cosmetically pleasing amputation, as the residual limb tends to be bulbous and early prostheses were considered unsightly.¹⁰ The malleoli are
trimmed to help decrease the size of the residual limb both for cosmetic reasons as well as to facilitate prosthetic fitting.⁸ Nonetheless, this amputation is more useful for locomotion, as there is an increased mechanical efficiency, which leads to a decreased metabolic cost of ambulation. The mechanical benefit is a result of a full-length prosthetic foot that provides a normal lever arm for push-off. The use of an energy storage and return prosthetic foot can further improve gait and walking speed while decreasing metabolic demand.²^,¹¹ The decrease in energy expenditure to ambulate is particularly advantageous in patients with diabetes, who generally have poorer baseline health and would be less likely to ambulate with a transtibial prosthesis.³

Indications

The indications for ankle disarticulation are diabetic infection, trauma, nonhealing diabetic and/or dysvascular ulcers, Charcot arthropathy, crush injury, frostbite, and congenital malformations, with the most common being diabetic infection. This results in two distinct patient populations: children with congenital anomalies and adults with vascular and/or immune compromise.¹² Approximately 7% of the US population has diabetes, and the incidence of amputation is increased 10-fold in these patients. In fact, patients with diabetes account for over two-thirds of all lower extremity amputations. Of course, the prerequisite for ankle disarticulation in all the aforementioned etiologies is a preserved heel pad with adequate blood flow. Therefore, the only absolute contraindication to an ankle disarticulation is a compromised heel pad, which may be the result of inadequate blood flow, infection, or soft-tissue loss.¹^,⁵

Unfortunately, this patient population often has decreased perfusion, and a major challenge is determining which patients have enough arterial flow to be able to heal an amputation at such a distal level. Many of these patients lack a palpable posterior tibial pulse, in which case the ankle-brachial index can be measured. Typically an ankle-brachial index of 0.5 or greater would indicate adequate flow, although patients with diabetes often have calcified arteries that may falsely elevate the ankle-brachial index. Another perhaps more accurate assessment of perfusion is measuring the transcutaneous partial pressure of oxygen, with values between 20 and 30 mm Hg indicative of adequate perfusion necessary for tissue healing.¹^,³ Other laboratory tests have long been used to help predict tissue healing capacity, including a serum albumin of at least 2.5 g/dL, and a total lymphocyte count of greater than 1,500 mm³. Although healing rates have been reported as low as 50%, studies have shown that when all the aforementioned criteria are met, healing rates can be as high as 88%.¹³^,¹⁴ Ultimately, if concerns about blood flow persist, a vascular surgery consult is warranted with options to include angioplasty or even bypass to increase perfusion. Others advocate for ankle disarticulation as a staged amputation before definitive transtibial amputation. Particularly in diabetic foot infection, a staged approach allows for source control of the infection and appropriate resuscitation before definitive amputation. This approach has been shown to decrease the risk of revision transfemoral amputation when compared with single-stage amputation¹⁵ (Figures 1 and 2).

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