Botulinum Toxin Effects on Plantar Ulcer Recurrence

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DESCRIPTION (provided by applicant): Patients with diabetes mellitus (DM) and peripheral neuropathy are at high risk for forefoot ulcers and subsequent lower extremity amputation. Total contact casting currently is the most effective treatment for healing neuropathic plantar ulcers but ulcer recurrence is high (20-70%) when patients discontinue casting. Plantar ulcers are associated with high plantar pressure. Limited ankle dorsiflexion has been believed to contribute to high forefoot plantar pressure and reulceration. Our recent randomized controlled trial found a 75% reduction in risk of reucleration at 7 months and a 53% reduction at 2 years when total contact casting was combined with a tendo-achilles lengthening. Forefoot peak plantar pressure was substantially reduced (27%) post-operatively but returned to pretreatment level within 7 months. The return of peak pressure was associated with the return of strength in the plantarflexor muscles while dorsiflexion range of motion remained increased throughout the study period. We hypothesize that the gradual return of high plantar pressures allowed the recently healed tissue to adapt to the stress and resist breakdown. In contrast, the recently healed tissue of those receiving total contact cast treatment alone immediately encountered high plantar pressures without this period of adaptation. Because the reduction in forefoot pressure was more "elated to reduced ankle strength than increased ankle motion, we will investigate if the novel therapeutic use of botulinum toxin injections, can temporarily weaken the plantarflexor muscles to produce a similar reduction in ulcer recurrence without the need for surgical intervention. The specific aims of this double blinded, placebo-controlled, randomized clinical trial are to determine the effects of botulinum toxin injections into the gastroc-soleus muscle of subjects with DM, peripheral neuropathy, and a forefoot ulcer on 1) ulcer healing time and ulcer recurrence rate and 2) impairments, functional limitations, and disability, and to 3) determine the appropriate therapeutic dose of botulinum toxin to achieve maximal therapeutic outcomes.