**8. Conclusions**

Sensory nerve grafts, allografts, and conduits all induce axons to regenerate across nerve gaps. Acellular allografts and conduits are considered to induce neurological outcomes only for nerve gaps <6 cm, although they are routinely used with reliability for "short" nerve gaps considered to be <3 cm, and allografts are FDA-approved only for repairing nerve gaps > 3 cm in length. All three techniques suffer the same imitations of decreasing efficacy with increasing gap length, increasing time between nerve trauma and repair, and increasing patient age. Although the distance across which allografts and conduits induce axon regeneration can be increased by modifying them in various ways, none of those techniques can be used clinically. Therefore, despite their limitations, sensory nerve grafts remain the clinical "gold standard" for repairing peripheral nerves [69,70,166,220–223]. The recovery of function across a 12-cm-long nerve gap of a 58-year-old patient, repaired 3.25 years post-trauma, suggests that functional recovery can be established, even when the values of all three injury parameters far exceed those where autografts are effective. Further testing and development of the technique are required to determine its reliability and the limits of its efficacy.

**Author Contributions:** Both authors contributed to the design, writing, and final editing of the paper. All authors have read and agreed to the published version of the manuscript.

**Funding:** This research received no external funding.

**Conflicts of Interest:** The authors declare no conflicts of interest.
