Clinical, Functional, and Sensorial Outcomes of the Agonist-Antagonist Myoneural Interface (AMI) Ewing Amputation

BACKGROUND: The Ewing Amputation is a modified approach to below-knee amputation (BKA) that incorporates the construction of Agonist-Antagonist Myoneural Interfaces (AMI) at the time of limb amputation. The AMI is a surgical construct in which naturally opposed, neurotized muscles are biomechanically linked in order to recreate the neural feedback loops present in intact human joints. We here present the long-term clinical outcomes amongst our lower extremity AMI amputee cohort and demonstrate a mitigation of phantom and residual limb pain, preservation of residual limb volume, and functional excursion of AMI constructs across the post-operative period. METHODS: We performed 36 Ewing procedures in a cohort of patients at Brigham & Women’s Hospital (BWH) and Brigham and Women’s Faulkner Hospital (BWFH) between July 2016 – March 2022. Outcomes were assessed prospectively over time and were clinical (demographics, surgical variations, complications), functional (construct excursion, prosthetic usage), and sensorial (residual limb pain, phantom pain, proprioception) in nature. RESULTS: Thirty-Six (36) Ewing patients were included in this study; 17 left (47.20%), 15 right (41.70%), and 4 bilateral (11.10%) for a total of 40 limbs. Patients were split between male (20, 55.60%) and female (16, 44.40%). Mean age at index amputation was 40.19 ± 11.11 years. Mean residual limb volume preservation at 12-months was 97.58% ± 4.13% of the preoperative state. Average construct excursion evidenced by ultrasound at 12-months post-operatively was 4.31mm ± 2.18mm, with strain relationships paralleling those of normal muscle dynamics. 72.20% (n=18) of patients reported no residual limb pain, 77.80% (n=18) reported no phantom limb pain, and 100.00% (n=15) reported anatomically correct phantom limb sensation at 12-months post-operatively. CONCLUSION: The Ewing amputation presents as a promising surgical intervention that can mitigate phantom and residual limb pain, preserve proprioception, and preserve residual limb volume.