Partial Foot Amputations and Disarticulations: Surgical Management

Terrence M. Philbin DO

Benjamin D. Umbel DO

Dr. Philbin or an immediate family member has received royalties from Arthrex, Inc., Crossroads, Fusion, IN 2 Bones, and Medline; is a member of a speakers’ bureau or has made paid presentations on behalf of Arthrex, Inc., Crossroads, IN 2 Bones, Medline, and Medshape; serves as a paid consultant to or is an employee of Artelon, Arthrex, Inc., Crossroads, IN 2 Bones, Medline, and Medshape; has stock or stock options held in Artelon, Crossroads, Medshape, and Tissue Tech; has received research or institutional support from Biomimetic, DJ Orthopaedics, and Zimmer; and serves as a board member, owner, officer, or committee member of AOAO Board of Directors. Neither Dr. Umbel 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 Philbin TM, Riley AJ: Partial foot amputations and disarticulations: surgical 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 453-461.

ABSTRACT

In the correct clinical scenario, partial foot amputation can be an appropriate and beneficial procedure. These amputations can provide a functional weight-bearing limb while decreasing patient morbidity and mortality. Potential benefits include increased independence and decreased energy expenditure when compared with more proximal amputations. Before surgery, it is important to select the most appropriate amputation level. Softtissue balancing becomes a critical component of the surgery with a more proximal partial foot amputation. In addition to patient selection and surgical technique, proper fitting, patient education, and use of an orthosis or prosthesis help to minimize the risk of complications, with the goal of providing good outcomes and maintain patients’ daily needs.

Introduction

The need for an amputation at any level is a life-changing event, increasing patient morbidity and ability to perform their activities of daily living. In the United States, amputation most commonly is necessitated by vascular insufficiency, a diabetes-related complication, trauma, or congenital deficiency.¹ Patients with diabetes are 10 times more likely to require an amputation at some level during their lifetime than the general population.¹ According to the Centers for Disease Control and Prevention, in 2010 there were 73,000 nontraumatic lower limb amputations in people with diabetes who were 20 years or older.² In 2016, about 131 million people worldwide had diabetes-related lower extremity complications, including 6.8 million amputations, according to the Global Burden of Diseases, Injuries, and Risk Factors Study.³

More than 60% of nontraumatic amputations occur in patients with diabetes.²^,⁴ After transtibial amputation, the 1-year mortality rate is 20.8% to 35.5%, and the 5-year mortality rate is 65%.⁵ A 2021 study found that for both patients with diabetes and without diabetes, 30-day mortality rate following lower extremity amputation was also significantly increased, with rates as high as 34% and 29%, respectively.³ One study interviewing 605 patients found that the Mental and Physical component summary scores of the Short Form health survey were found to be significantly lower for amputees when compared with those for the general population.⁶

Although it is unclear whether these poor outcomes are related to the amputation level or the underlying disease process, a more distal amputation is preferable to a transtibial amputation. If possible, foot and ankle surgeons use partial foot amputation as a salvage procedure, so that the patient can retain a functional weight-bearing residual limb.⁴ Compared with transtibial amputation, partial foot amputation requires less energy expenditure for ambulation and may allow the patient to retain greater independence.⁴^,⁵ Transmetatarsal amputation has a lower mortality rate 1 and 3 years
after surgery, compared with transtibial amputation.⁵ Because a salvage partial foot amputation greatly reduces the area of weight bearing on the foot, proper fitting and use of an orthosis or prosthesis are essential. This factor is even more critical if the patient has impaired sensation.⁷ When deciding on the level of partial foot amputation, options include ray resection, transmetatarsal, Lisfranc tarsometatarsal, and hindfoot (Chopart, Boyd, and Pirogoff) amputation (Figure 1).

FIGURE 1 Schematic drawing showing some of the levels of partial foot amputation or disarticulation. (Adapted from Witt BL, Philbin TM: Midfoot amputations, in Flatow E, Colvin EC, eds: Atlas of Essential Orthopaedic Procedures. American Academy of Orthopaedic Surgeons, 2013, pp 551-556.)

Preoperative Evaluation

A thorough preoperative patient assessment is critical in evaluating patients who may require surgical intervention for limb salvage. This assessment begins with a comprehensive current and past medical history, particularly in patients with diabetes, who may have other risk factors for peripheral arterial disease. Peripheral arterial disease in itself may predispose patients to foot ulcers and compromise the ability for healing of more distal partial foot amputations. Physical examination and evaluation of limb perfusion are useful in determining whether a patient can benefit from a partial foot amputation rather than amputation at a more proximal level.⁵^,⁸^,⁹ The level of amputation most commonly is determined by the location of necrotic tissue, the distal extent of the viable soft-tissue envelope, and the potential ambulatory status of the patient.¹⁰^,¹¹ The goal of a partial foot amputation is to salvage the foot at a level at which the soft-tissue envelope will heal, without concern for further breakdown during the patient’s lifetime.⁷

Limb Perfusion Assessment

Limb perfusion can be noninvasively assessed using transcutaneous oxygen tension, the ankle-brachial index (ABI), arterial Doppler ultrasound studies, toe systolic blood pressures, and toe brachial indices.⁷^,¹²^,¹³ An ABI lower than 0.9 is considered abnormal, and the likelihood of healing is poor if the ABI is lower than 0.45;⁷^,⁸^,¹⁴ however, the ABI may be inaccurate in a patient with calcification of the blood vessels.¹⁵ ABIs have a moderate predictive value in diagnosing peripheral arterial disease.¹⁶ However, when planning surgical intervention in these patients, ABI can be combined with advanced imaging (Doppler ultrasound or peripheral CT angiogram) to better characterize the underlying arterial disease.¹⁶ Toe brachial indices and toe systolic blood pressures appear to be more accurate than the ABI in patients with diabetes or peripheral vessel calcifications because the digital arteries are less commonly affected by calcifications when compared with larger arteries about the ankle and remain compressible for obtaining accurate pressure readings.¹⁵^,¹⁷ The toe brachial indices and toe systolic blood pressures are obtained by inflating a cuff on the toe. These tests may not be feasible when very distal toe necrosis or toe ulceration is present in an area where the cuff would be placed.¹⁷^,¹⁸

When assessing for level of adequate perfusion, arterial Doppler ultrasound is the most useful initial screening test to determine if vascular consultation or arteriogram is indicated.¹⁹ Biphasic or triphasic signal on arterial Doppler ultrasound indicates a healthy vessel, but monophasic signal indicates a diseased artery. The likelihood of a successful distal amputation often can be increased by preamputation use of endovascular methods or surgical revascularization of the lower limb; therefore consultation with a critical limb or vascular surgery service may be helpful for preoperative planning. At least 72 hours should elapse between the revascularization and the amputation.¹⁴ However, although a thorough preamputation assessment with diagnostic imaging and specialty consultation is important in assessing patients with peripheral vascular disease, one study found that these interventions did not necessarily lead to more limb-saving revascularizations in patients with chronic kidney disease. This highlights the issue that more effective preventive therapies are still needed to reduce amputation in at-risk populations.²⁰

Evaluating for distal healing potential can best be done with transcutaneous tissue oxygen tension, which is a measurement of the amount of oxygen that has diffused across capillaries to the epidermis.¹⁹ This test can reliably and easily be used in all patients.¹³^,¹⁵^,²¹ A tension measurement higher than 30 mm Hg suggests adequate healing potential; a measurement lower than 20 mm Hg is predictive of wound-healing failure.⁷^,⁸^,¹³^,¹⁴^,²² Position of the limb during this assessment is important. Yang et al²³ assessed 61 patients with diabetes with foot ulcers and measured their transcutaneous oxygen pressure
(TcPO₂). They found that in the supine position, a TcPO₂ > 25 mm Hg was the most predictive cut-off point for healing of diabetic foot ulcers, with all wounds healing when the TcPO₂ was >40 mm Hg. Because this test does not rely on the mechanical compression of arteries, it is well suited to patients with diabetes or arterial calcification.¹⁵ Andrews et al¹³ recommended using both this test and those previously described in deciding on an amputation level. In a study of 261 patients with diabetes, Faglia et al¹⁸ found that transcutaneous tissue oxygen tension was a more reliable test than ankle or toe pressures and that it could be used independently in risk stratification for limb ischemia. The primary disadvantage to the use of this test is the time needed to calibrate and equilibrate the machine after attachment to the patient and before measurements are obtained.¹³ In addition, the measurements can be inaccurate in the presence of infection or peripheral edema.²⁴

Imaging

Three radiographic views of the foot and ankle should be obtained, and they should be weight bearing if possible.⁸ Additional imaging studies sometimes are useful for further delineating the extent of soft-tissue or bony involvement and deciding on the amputation level. MRI can best depict soft-tissue masses, fluid collections, or osteomyelitis. CT can show subtle osseous changes such as fractures, periosteal reactions, or sequestra. Indium-111-labeled white blood cell scans can detect focal areas of infection, such as osteomyelitis, and can differentiate an infectious from a noninfectious process.²²

Metabolic and Nutritional Status

Maximizing the patient’s metabolic and nutritional status is an important part of preoperative optimization of wound-healing potential. Proper control of blood glucose levels in a patient with diabetes is essential for lowering the risk of infection and improving the healing ability of surgical wounds.⁷^,⁸^,⁹^,¹⁰ Partial foot amputation is less likely to succeed in a patient with a hemoglobin A1c level higher than 8.0%.⁵ A serum albumin level higher than 3.0 g/dL, total serum protein level greater than 6.0 g/dL, or hemoglobin levels greater than 11.0 g/dL are values that likely represent adequate nutritional status needed for wound healing.⁷^,⁹^,¹⁹ Additionally, greater preoperative albumin levels have been shown to be statistically significant in predicting clean surgical margins in partial foot amputations in patients with diabetic foot osteomyelitis.²⁵ Historically, a lymphocyte count higher than 1,500 cells/µL was considered to indicate high wound-healing capacity, but Pinzur et al²⁶ found that this measurement was not prognostic.

General Surgical Considerations

The patient is positioned supine on the operating table with a bump underneath the ipsilateral hip to limit external rotation of the lower limb.⁸^,²⁷^,²⁸^,²⁹ Planned skin incisions are marked to indicate the position of future skin flaps. In an amputation necessitated by infection, exsanguination of the limb historically has been avoided because of the theoretic risk of spreading the infection proximally.¹² However, this practice is not known to be supported by research. It is acceptable to use a tourniquet to limit blood loss when infection is present, but exsanguination of the limb is not recommended before inflation of the tourniquet. Placement of the tourniquet over an area of vascular bypass grafts or stents should be avoided because of the theoretic risk of injury, although this recommendation is also historical and not supported by known studies.¹² Alternatively, an Esmarch bandage can be used as an ankle tourniquet in a distal procedure.¹²^,³⁰

As a general surgical principle, obtaining intraoperative proximal surgical margins free of infection should always be the goal when performing partial foot amputations. In a prospective study of 72 patients, proximal margins deemed clean by postoperative histopathologic analysis resulted in improved patient outcomes and lower postoperative complication rate. The authors noted that postoperative wound dehiscence, re-ulceration, and need for re-amputation were decreased in patients where a clean margin was successfully obtained.²⁵

Ray Resection

Outcome Considerations

In an appropriate patient, ray resection can be more durable and functional than a transmetatarsal amputation.¹²^,²⁸ Depending on the functional status of the patient, a single ray resection, particularly of the lateral column, may allow for ambulation with normal shoe wear and only minor insole modifications. Ray resection is used only if necrosis and soft-tissue loss are limited and is most successful if no more than two rays are resected.⁸^,¹²^,²⁸ Resection of the lateral rays best maintains the foot balance needed for ambulation.⁸ Partial resection of the medial forefoot tends to increase stress at the lateral border of the foot, which can lead to transfer lesions throughout the forefoot.³¹ Resection of the first ray leads to loss of the anterior tibial tendon insertion, which decreases the dorsiflexion power of the ankle and increases pronation of the forefoot. Resection of the first ray also leads to instability of the medial column during the terminal stance phase of gait because of the loss of the flexor hallucis brevis and flexor hallucis longus insertions.³² If the entire fifth metatarsal is resected, including the base, the peroneus brevis insertion is lost, causing loss of eversion strength and contributing to varus deformity of the hindfoot unless it is reattached to a surrounding structure.⁸^,²⁸ Patients should be informed that claw toes may develop after ray resection because of loss of balance of the intrinsic musculature. A 2019 retrospective study of 185 patients found that ray resection is a viable option after proper patient selection. An overall failure rate (requiring further major amputation) of 11.9% and overall revision rate of 38.4% were noted. Additionally, postoperative re-ulceration was significantly associated with revision surgery and occurred at, on average, 19.5 months from the time of the index ray resection.³¹ Therefore, the authors concluded that prevention
of ulcer recurrence was paramount in preventing further revision surgery.³¹

FIGURE 2 AP radiograph showing resection of the entire fifth ray with transfer of the peroneus brevis insertion to the cuboid.

Figure 2 shows a radiograph of an entire fifth-ray resection in which the peroneus brevis insertion was transferred to the cuboid.

Surgical Technique

A dorsal longitudinal skin incision is made along the affected metatarsal. At the level of the metatarsophalangeal joint, the skin incision is continued through the adjacent web space to the plantar aspect of the foot.²⁸ The sensory nerves are identified just deep to the skin incision, gentle traction is applied, and the nerve is transected sharply with the scalpel and allowed to retract proximally. The extensor tendon is identified and transversely incised at the level of the tarsometatarsal joint. Proximally, the lumbrical and interosseous muscles are identified and transversely incised. At this point, the base of the metatarsal is identified. If possible, the metatarsal distal to the base should be resected to preserve the tarsometatarsal joint and the transverse metatarsal arch.⁸^,²⁸ An oscillating saw is used to make a transverse cut in the proximal metatarsal. If any of the metatarsal remains, the distal end is beveled at roughly 30° to 45°, from dorsal-distal to plantar-proximal, to prevent soft-tissue irritation on the residual plantar foot during the late stance phase of ambulation.³³ If the entire metatarsal is to be resected, however, a disarticulation of the tarsometatarsal joint is substituted. The proximal aspect of the metatarsal is lifted out of the wound, and the soft tissues deep to the metatarsal are identified. The flexor tendon is transected transversely, and all soft-tissue attachments to the metatarsal are carefully removed in a proximal-to-distal fashion.²⁸ The metatarsal can then be removed.

After the metatarsal is removed, the remaining adjacent metatarsophalangeal joint capsules are anchored together using 0 nonabsorbable suture.²⁸ This step is intended to hold the adjacent metatarsal heads in proximity as the soft tissue heals. A small drain can be placed into the void between the remaining metatarsals, if desired. The subcutaneous tissue is approximated using 3-0 absorbable suture, and the skin is approximated using 3-0 nylon suture. A well-padded posterior splint is placed onto the limb with mild compression to hold the metatarsal heads in proximity.²⁸

Transmetatarsal Amputation

Outcome Considerations

If soft-tissue or bony involvement precludes an isolated ray resection, transmetatarsal amputation historically has led to excellent long-term function and ambulation as well as decreased energy expenditure and risk of mortality.⁵^,⁸^,⁹^,¹¹^,²⁷ Transmetatarsal amputation first was described in 1949 by McKittrick, and approximately 10,000 of these procedures are performed in the United States each year.⁸^,⁹^,¹² The benefits of a transmetatarsal amputation over a more proximal resection include maintenance of the anterior tibial and peroneus brevis insertions, which helps maintain power of ankle motion, ankle stability, and forefoot balance.⁸^,¹¹^,³⁴ Younger et al³⁵ found that the most important predictor of success in transmetatarsal amputations was a hemoglobin A1c level lower than 10%. To avoid wound-healing complications, a patient’s diabetes should be well controlled before surgery. The surgeon should assess for an Achilles tendon contracture and, if necessary, should lengthen the tendon during the index surgery to avoid equinus positioning of the residual limb.⁸^,¹¹^,²⁷^,³⁵ Careful attention should be given to the metatarsal cuts to maintain a balanced cascade because the tarsometatarsal joint is more proximal as it progresses from medial to lateral. A poorly resected cascade is a major cause of wound complications or recurrent ulceration after transmetatarsal amputation.⁷^,¹⁹ Despite proper patient selection and surgical technique, one systematic review found revision to major amputation to be as high as 33.2% following the index procedure.³⁶ Harris and Fang³⁷ found in their retrospective review that neuropathy and a positive metatarsal bone margin following surgery significantly affected transmetatarsal wound healing.

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