Transmetatarsal amputation (TMA) is an effective procedure, which preserves limb length while treating forefoot pathology that necessitates amputation in patients with adequate circulation. Success rates range from 39.4 percent to 93.3 percent.1-14 The most commonly reported complications of a TMA are an equinus or equinovarus deformity of the residual foot, and recurrent ulceration.5,8,15-19
Rates of recurrent ulceration, in studies with a minimum of 12 months postoperative follow-up, range from 6.5 percent to 17.3 percent.2,7,10,11,13 Recurrent ulcerations occur secondary to an equinus or equinovarus deformity of the residual foot.5,15,16,18-20 These deformities are typically present as reducible deformities at the time of the definitive TMA procedure and become fixed deformities over time.21
When patients have peripheral neuropathy, the aforementioned rigid deformities, do not obtain routine foot care and ambulate either barefoot or in inappropriate shoe gear, they may have increased localized pressure leading to callus formation and subsequent ulceration. This often necessitates a more proximal amputation or an aggressive arthrodesis procedure to correct a now fixed deformity.
An equinus deformity becomes worse after a TMA due to loss of the insertions of extensor hallucis longus and extensor digitorum longus. This leaves only the anterior tibial tendon in the anterior muscle compartment, which is overpowered by the pull of the gastrocnemius-soleus.19,22,23
A varus deformity of the residual foot is due to three factors.
First, loss of the forefoot eliminates the weightbearing aspect of the transverse arch of the foot, resulting in a varus posture of the residual foot.3 Second, the loss of the insertions of the intrinsic musculature of the foot and plantar fascia leads to instability of the residual foot and loss of the windlass mechanism, which is responsible for raising the longitudinal arch of the foot with subsequent lowering the medial aspect of the foot. Third, the peroneus brevis is overpowered by the anterior tibial and posterior tibial tendons, leading to exaggeration of subtalar joint pronation and varus deformity of the residual foot.19,22,23
What The Research Reveals About Adjunctive Achilles Tendon Procedures With TMAs
To address an equinus deformity, many podiatric surgeons will consider performing an adjunctive Achilles tendon procedure when performing a TMA. To date, two studies have reported on the efficacy of an Achilles tendon procedure on healing or maintaining a healed skin envelope in patients who have undergone a TMA and had a recurrent ulceration.24,25
Barry and colleagues reported on 31 patients (33 feet) who underwent an Achilles tenotomy for treatment of a recurrent ulceration, which developed after a TMA.24 The follow-up period was 27 months. They noted a healed recurrent ulceration in a total of 30 feet (90.9 percent). One patient was lost to follow-up. One patient remained with a non-healing superficial ulceration with the reason for continued non-healing not reported. The remaining patient had progressive ischemia, which necessitated a below-knee amputation (BKA). Five feet (6.1 percent) developed heel ulcerations with four being plantar central and related to over-lengthening of the Achilles tendon, and one being a decubitus ulceration.24
La Fontaine and co-workers reported on 28 patients (28 feet) who underwent a percutaneous Achilles tendon lengthening for treatment of a recurrent ulceration, which developed after a TMA.25 The follow-up period was 29 months. A total of 24 feet (85.7 percent) healed their recurrent ulceration. The reason for continued non-healing of the remaining four ulcerations was not reported. Six patients (21.4 percent) developed new ulcerations. Five of these ulcerations occurred on the plantar central heel and were related to over-lengthening of the Achilles tendon. One ulceration occurred on the plantar lateral aspect of the foot and was likely secondary to a forefoot varus deformity, which was not addressed.25
Addressing The Residual Varus Deformity After TMAs
While an Achilles tendon lengthening procedure has become a common adjunctive procedure to a TMA, few have published on tendon balancing procedures to address a residual varus deformity resulting from a TMA. Some studies have discussed the use of a split anterior tibial tendon transfer to correct a residual varus deformity. However, no studies to date have reported on the results of this procedure to prevent or treat a recurrent ulceration following a TMA.19,23
Currently, there are published results for only three surgical techniques employed as adjunctive procedures to a TMA to correct a residual varus deformity of the foot and prevent recurrent ulceration. These three techniques are: 1) intramedullary screw placement; 2) flexor hallucis longus and extensor digitorum longus tendon transfers; and 3) peroneus brevis to peroneus longus tendon transfer.14,23,26-28
Pertinent Tips On Intramedullary Screw Fixation
Surgeons would perform intramedullary screw fixation while the residual foot is held in a neutral position. One would insert the screw down the residual first metatarsal into the rearfoot, ensuring that the distal tip of the screw does not enter the ankle joint and that the head of the screw is seated well within the residual first metatarsal. Then cover the distal residual first metatarsal with autogenous or allogenic bone graft substitute or the muscle belly of the abductor hallucis to prevent hardware exposure should the incision dehisce or have delayed healing.
Using an intramedullary screw has an advantage with there being no need for additional incision placement. Potential complications include infection, hardware migration, iatrogenic fracture and recurrent ulceration. Intramedullary screw fixation results in static correction of a varus deformity of the residual foot. One must take care to ensure the residual foot is held in a neutral position as the midfoot will be stiff postoperatively and any varus or valgus position of the residual foot could result in recurrent ulceration.14,23
Can Tendon Balancing Procedures Have An Adjunctive Impact?
In regard to flexor hallucis longus and extensor digitorum longus tendon transfers, surgeons transfer the flexor hallucis longus and the tendon slips of the extensor digitorum longus to the residual first and fourth metatarsal respectively via drill holes. One then secures these transfers while the residual foot is held in a neutral position to create a dynamic correction of varus deformity of the residual foot. This procedure has the same advantage as intramedullary screw placement with no need for additional incisions.14,28
Surgeons would perform transfer of the peroneus brevis to the peroneus longus either through an incision on the lateral foot or distal lateral leg. One transects the peroneus brevis tendon via electrocautery and weaves it through the peroneus longus tendon in a Pulvertaft weave fashion while the residual foot is held in a neutral position. This results in dynamic correction of a varus deformity of the foot due to the increased pull on the medial aspect of the residual foot. The advantages of incision placement on the distal lateral leg, as opposed to the lateral foot, are increased healing potential — paramount in patients with vascular compromise — and the lack of need for reconstruction of the peroneal tendon sheath.14,27
Roukis and colleagues reported on a total of 29 patients (29 feet) who underwent a TMA.14 Twenty-seven patients (27 feet) had an equinus deformity present with 26 undergoing a percutaneous Achilles tendon lengthening or gastrocnemius recession. Twenty-two feet had a residual forefoot varus deformity with 17 feet undergoing correction. Surgeons used an intramedullary screw in five cases, performed flexor hallucis longus and extensor digitorum longus tendon transfers in five cases, and performed a peroneus brevis to peroneus longus tendon transfer in seven cases. The researchers did not perform tendon balancing procedures if they deemed them unnecessary or unfeasible due to limited regional perfusion.
Only three patients, none of whom underwent any tendon balancing procedures, ulcerated on the plantar lateral aspect of the residual foot with one requiring a Chopart amputation, one requiring a BKA and one cardiac-related death. The study authors reported no hardware infections with the use of intramedullary screw placement. One patient had transient eversion weakness after the peroneus brevis to peroneus longus tendon transfer. However, this resolved with self-directed physical therapy of performing daily dorsiflexion-eversion exercises of the residual foot. The study authors found no other complications.
The goal of any limb salvage procedure is to create a stable, plantigrade foot. One can protect the foot postoperatively in a shoe or brace, which allows maintenance of function while withstanding repeated stress that occurs during ambulation.
A TMA is effective in facilitating these goals as one can maintain limb length and protect the residual foot in shoe gear with a custom insert, with or without adjunctive bracing, for continued ambulation. The most common reported complications of a TMA are an equinus or equinovarus deformity of the residual foot and recurrent ulceration. Various researchers have also described these complications as the most common technique-based complications of a TMA. While the addition of an Achilles tendon procedure has become a common adjunctive procedure to a TMA, one also needs to address correction of the dynamic varus deformity of the residual rearfoot in order to minimize recurrent ulceration following a TMA.
Dr. Schade is the Chief of the Limb Preservation Service for the Madigan Healthcare System in Tacoma, Wa. She is an Associate of the American College of Foot and Ankle Surgeons.
Dr. Steinberg is an Associate Professor in the Department of Plastic Surgery at the Georgetown University School of Medicine in Washington, D.C. He is a Fellow of the American College of Foot and Ankle Surgeons.
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