Variation on a technique for the intra-muscular insertion of nerve endings to minimise neuropathic and residual pain in lower limb amputees: a retrospective cohort study

INTRODUCTION: A major cause of morbidity in lower limb amputees is phantom limb pain (PLP) and residual limb pain (RLP). This study aimed to determine whether a variation of the surgical technique of inserting nerve endings into adjacent muscle bellies at the time of lower limb amputation can decrease the incidence and severity of PLP and RLP. METHODS: Data were retrospectively collected from January 2015 to January 2021, including eight patients that underwent nerve insertion (NI) and 36 that received standard treatment. Primary outcomes included the 11-point Numerical Rating Scale (NRS) for pain severity, and Patient-Reported Outcomes Measurement Information System (PROMIS) pain intensity, behaviour, and interference. Secondary outcome included Neuro-QoL Lower Extremity Function assessing mobility. Cumulative scores were transformed to standardised t scores. RESULTS: Across all primary and secondary outcomes, NI patients had lower PLP and RLP. Mean ‘worst pain’ score was 3.5 out of 10 for PLP in the NI cohort, compared to 4.89 in the control cohort (p = 0.298), and 2.6 out of 10 for RLP in the NI cohort, compared to 4.44 in the control cohort (p = 0.035). Mean ‘best pain’ and ‘current pain’ scores were also superior in the NI cohort for PLP (p = 0.003, p = 0.022), and RLP (p = 0.018, p = 0.134). Mean PROMIS t scores were lower for the NI cohort for RLP (40.1 vs 49.4 for pain intensity; p = 0.014, 44.4 vs 48.2 for pain interference; p = 0.085, 42.5 vs 49.9 for pain behaviour; p = 0.025). Mean PROMIS t scores were also lower for the NI cohort for PLP (42.5 vs 52.7 for pain intensity; p = 0.018); 45.0 vs 51.5 for pain interference; p = 0.015, 46.3 vs 51.1 for pain behaviour; p = 0.569). Mean Neuro-QoL t score was lower in NI cohort (45.4 vs 41.9; p = 0.03). CONCLUSION: Surgical insertion of nerve endings into adjacent muscle bellies during lower limb amputation is a simple yet effective way of minimising PLP and RLP, improving patients’ subsequent quality of life. Additional comparisons with targeted muscle reinnervation should be performed to determine the optimal treatment option.