Factors Associated with Successful Pain Mitigation Following Primary and Secondary Targeted Muscle Reinnervation in Amputees
Floris V. Raasveld, MD1, Maximilian Mayrhofer-Schmid, NA2, Barbara Gomez-Eslava, MD, MS1, Yannick Albert J. Hoftiezer, MD1, Ian L Valerio, MD, MS, MBA1 and Kyle R. Eberlin, MD1, (1)Massachusetts General Hospital/Harvard Medical School, Boston, MA, (2)Heidelberg Medical School, Heidelberg, Germany
Introduction: Targeted Muscle Reinnervation (TMR) is an effective modality in the surgical management of neuropathic pain for in amputees. TMR can be performed primarily (within 14 days of amputation) for prevention, or secondarily (>14 days post-op) for treatment of neuropathic pain. While certain patients may experience significant pain relief and cases of complete pain absence have been reported, the specific patient cohort for whom this technique is most effective is not known.
Methods: Amputees who underwent TMR between 2018 through 2023, enrolled in our prospective data repository, with a minimum follow-up of 6 months, were included. Demographic, surgery-related and pain data (0-10 numerical pain scale (NRS)) were analyzed. Sustainable pain mitigation (NRS of ≤3/10 for ≥3 months until last follow-up) was defined as pain remission for secondary TMR cases, and pain prophylaxis for primary TMR patients. Multilevel mixed-effects models were utilized to analyze pain difference and to visualize postoperative pain courses.
Results: A total of 115 amputees were included (median follow-up was 1.9 years (IQR: 1.0-2.8)), of which 48 patients (41.7%) underwent Primary TMR and 67 patients (58.3%) underwent Secondary TMR. Following primary TMR, 45.8% of patients achieved sustainable pain prophylaxis and demonstrated significantly lower pain scores during all first 24 postoperative months (p<0.001), compared to other patients (Fig. 1). Following Secondary TMR, 22.4% of patients achieved sustainable pain remission and demonstrated significantly lower pain levels at 12 (p=0.046), 18 (p=0.040) and 24 (p=0.024) months postoperative compared to other patients (Fig. 2). Complete pain disappearance (NRS of 0/10 for ≥3 months until the last follow-up) was reported by 16.7% of primary, and 3.0% of secondary TMR patients. Primary TMR patients have significantly higher odds (OR=2.70; 95% CI 1.30-5.61; p=0.0070) of achieving pain mitigation than secondary TMR patients. In primary TMR patients, effective pain prophylaxis was associated with an absent history of depression (p=0.025), absent post-traumatic stress disorder (p=0.040), and absent smoking (p=0.021). In secondary TMR patients, higher BMI (p=0.005), absence of psychiatric diseases (p=0.021) and peripheral vascular disease (p=0.024) were associated with sustainable pain remission.
Conclusions: Following TMR, average pain improvement was observed for both primary and secondary TMR patients. Patients undergoing primary TMR demonstrate a higher odds of achieving optimal pain outcomes. Psychiatric comorbidities appear to be a risk factor for worse outcomes in both groups. These findings may assist in pre-operative patient selection for TMR surgery in the management of neuropathic pain.
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