Targeted Muscle Reinnervation Helps Reduce—and Prevent—Pain in Amputees
Symptomatic neuromas have long been a problem for amputees, interfering with prosthetic comfort and causing residual pain that often requires treatment. During the last 15 to 20 years, surgeons have used targeted muscle reinnervation (TMR) and regenerative peripheral nerve interface (RPNI) procedures to improve symptoms from neuromas. In TMR, surgeons transfer a mixed or sensory nerve to a “target” transected motor nerve to prevent disorganized axonal growth. RPNI is a less complicated procedure during which the free nerve end is implanted into a denervated free muscle graft, again to decrease disorganized sprouting of axons.
Advances in amputee care at US military centers, driven largely by recent overseas conflicts, have shown anecdotally that TMR and RPNI prevent neuroma formation when used prophylactically during initial amputation, and that they also relieve pain when used as secondary treatment for existing neuromas. In the April 22, 2021 issue of The Journal, Hoyt et al. reviewed records from Walter Reed National Military Medical Center to evaluate changes in pain scores, symptom resolution, and frequency of complications when TMR and/or RPNI were utilized.
The authors analyzed 87 nerve interface interventions in 80 lower extremity amputations that had at least 6 months of follow-up. Fifty-nine of the procedures (68%) were done to treat symptomatic neuromas at a median of 6.5 years after amputation, while 28 procedures (32%) were done for primary prophylaxis. Hoyt et al. found that the sciatic nerve was most likely to develop symptomatic neuromas after amputations at or above the knee, while the tibial and peroneal nerve distributions were most commonly symptomatic after amputations distal to the knee. TMR was utilized alone in 85% of the cases, and surgeons used RPNI most frequently to prevent pain in the sural and saphenous nerves.
Overall, symptom resolution after all procedures was 92% at the final follow-up. VAS pain scores improved from 4.3 to 1.7 points in the delayed-treatment group and did not vary by amputation level. The final mean pain score in the primary-prophylaxis group was 1.0 ±1.9. There were no significant differences in pain outcomes between the primary and delayed groups, but 6 patients in the delayed cohort required revision for residual limb or phantom limb pain. In patients with transtibial amputations, failure to address an asymptomatic tibial nerve during delayed TMR resulted in an increased risk of revision surgery.
Although retrospective in nature, this study shows some encouraging early data to support the primary and secondary use of TMR/RPNI in amputee care. More research is required to determine whether these results in wounded warriors can be replicated in a civilian amputee population.
Click here for a Commentary on this study by Ann R. Schwentker, MD.
Matthew R. Schmitz, MD
JBJS Deputy Editor for Social Media