Back to 2026 Abstracts
Biomechanical limits to daily progressive lengthening approaches that facilitate end-to-end peripheral nerve repair
Elisabeth Orozco, M.S.
1, Justin M. Brown, MD
2; Sameer B. Shah, PhD
3(1)University of California, San Diego, La Jolla, CA, (2)Massachusetts General Hospital, Department of Neurosurgery, Paralysis Center, Boston, MA, (3)VA San Diego Medical Center, San Diego, CA
Introduction: We recently demonstrated the superiority of a tension-based strategy for nerve repair versus autografts, for large-gap nerve injuries. Specifically, nerve-lengthening devices were implanted in a 3cm rabbit sciatic nerve gap; proximal stumps were progressively lengthened towards the distal stump via daily actuation over two weeks, and end-to-end repair performed upon device explantation. Neuromuscular outcomes were superior to those measured in autograft-based repairs. Several questions remain unanswered regarding this promising approach, including determining thresholds for daily nerve lengthening rates and evaluating the extent to which lengthened nerves restore their pre-injury morphology.
Materials and Methods:Experiments were performed under IACUC approval. A 10mm sciatic nerve gap was created in male Lewis rats. For device-based repairs, proximal and distal stumps were safely secured in custom-designed nerve interfaces. The proximal stump was progressively drawn towards the distal stump. Nerves were lengthened daily by 1mm/day (conservative; <15% deformation); 2mm/day (moderately aggressive; <25% deformation); 3mm/day and 4mm/day (very aggressive, >30% and >40% deformation, respectively). After lengthening for up to 2 weeks (duration dependent on lengthening rate), devices were removed. Nerve stumps were trimmed and sutured directly end-to-end, tension-free. Excised and flipped 10mm autografts were used as standard of care controls. 1 month and 3 months after initial injury, structural and functional outcomes were compared (8 animals/group). Neuromuscular structural regeneration was evaluated through immunohistochemistry. Nerves were immunolabeled with nodal markers, beta3-tubulin, and laminin to evaluate the morphology of lengthened nerves in the proximal stump and regenerated axonal counts/density in the distal stump. Sciatic function index and ankle dorsiflexion torque were evaluated as functional outcomes. Outcomes were compared using Analysis of Variance.
Results: Lengthening at 4mm/day damaged nerves by the second day of actuation; end-to-end repairs could not be performed. Nerves lengthened at 3mm/day were under significant tension during stretch and incurred intra-fascicular damage; however end-to-end repairs could be performed. End-to-end repairs were readily performed after lengthening at 1mm/ or 2mm/day. Correspondingly, at three months, structural regenerative outcomes (distal axon counts) and functional regenerative outcomes (ankle dorsiflexion torque) in 1/ and 2mm/day groups were both superior to autograft-based outcomes and to the 3mm/day group. Bands of Fontana were restored and internode distance increased in proximal stumps within 1 month.
Discussion/Conclusion: Progressive nerve lengthening with daily strains up to 25 facilitates end-to-end repair, enhancing regenerative outcomes for large nerve gaps versus gold-standard autografts. Tension-based strategies offer a promising alternative to graft-based approaches for large nerve gap injuries.
Back to 2026 Abstracts
