Targeted Muscle Reinnervation Reduces Pain and Improves Ambulation in Patients Undergoing Below-Knee Amputation: A Single-Institution Matched Cohort Study

Abstract

Each year, 200,000 people will undergo a lower extremity amputation; 80% of those patients require an amputation because of critical ischemia or infection. After amputation, patients suffer from chronic pain, inability to ambulate, and high mortality rates. Targeted muscle reinnervation (TMR) is a nerve transfer procedure that redirects the surgically transected major sensory nerves into redundant motor nerves to prevent or to treat both neuroma and phantom limb pain. The purpose of this study was to evaluate the effect of TMR on pain and ambulation when it is performed at the time of below-knee amputation (BKA). This is a matched cohort study comparing 100 consecutive patients undergoing BKA with primary TMR and 100 consecutive patients undergoing BKA who were treated with traditional traction neurectomy. Patients’ charts were reviewed for the comorbidities in the Charlson Comorbidity Index. Postoperative clinic notes were reviewed for the presence of residual and phantom limb pain, severity of overall pain, and ambulatory status. Pharmacy records were reviewed for opioid and neuroleptic medication use. Obituary data were reviewed to determine mortality rates. There were 100 patients included in the TMR group, with an average age of 60 years and body mass index of 29 kg/m2; 84% had diabetes, 55% peripheral vascular disease, 43% end-stage renal disease on dialysis, 17% with a prior myocardial infarction, and 13% with a prior cerebrovascular accident. Average time to follow-up was 6.2 months for the TMR group and 18.7 months for the non-TMR group; 73% of TMR patients were pain free compared with 34% of non-TMR patients (P < .01). Average pain was 2.6 of 10 for the TMR group and 5.4 of 10 for the non-TMR group (P < .01); 14% of TMR patients endorsed residual limb pain compared with 59% of non-TMR patients (P < .01), and 18% of TMR patients endorsed phantom limb pain compared with 49% of non-TMR patients (P < .01). Compared with 26% of non-TMR patients, 6% of TMR patients were taking opioids (P < .01); 42% of TMR patients were taking neuroleptic medications compared with 50% of non-TMR patients (P = .15). Compared with 72% of non-TMR patients, 93% of TMR patients were ambulatory (P < .01). There was no significant difference in 12-month mortality rate (4.9% vs 6.0%; P = .80). When it is performed immediately at the time of BKA, TMR significantly reduces pain and improves ambulation in patients critically threatened by ischemia or infection. Optimizing pain and ambulation may be critical in improving further morbidity and mortality rates in this comorbid population of patients.