THE EVIDENCE

For gaps under 30mm, synthetic nerve conduits do the job. They provide a protected pathway for axon regrowth, maintain neurotrophic gradients, and avoid donor site morbidity. Moore et al. (2009) showed equivalent outcomes to autografts in a randomized trial for digital nerve gaps under 20mm.

But cross the 30mm threshold and the picture changes. Axons need viable Schwann cells to guide them across the gap. In short gaps, conduits preserve enough endogenous Schwann cell migration from the proximal stump. In long gaps, the Schwann cell front dies out before axons arrive.

Autografts solve this by bringing their own Schwann cells. The grafted nerve segment contains pre-aligned Schwann cells that support axon regrowth across much longer distances—up to 50-70mm in clinical practice. But you pay for this with donor site morbidity: sensory loss, neuroma formation, and sometimes worse outcomes at the donor site than the repair.

THE HYBRID APPROACH

Nerve allografts (cadaveric nerve) provide the Schwann cell scaffold without donor site morbidity. Brooks et al. (2012) showed processed nerve allografts bridging gaps up to 50mm with outcomes approaching autograft standards.

Bioengineered conduits are catching up. Neurotrophic factor delivery (GDNF, BDNF) maintains Schwann cell viability longer. Intraluminal scaffolds provide physical guidance. Electrical stimulation accelerates axon outgrowth. Clinical trials are testing these combinations now.

THE QUESTION

Can we make conduits match autografts for long gaps? Or should we stop trying to replace the gold standard and instead focus on expanding allograft availability?

Research synthesis via Aubrai.