Key Insights On Adjunctive Procedures With Transmetatarsal Amputations

Valerie L. Schade, DPM, AACFAS

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

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