Introduction: In head and neck surgery, radiation therapy is often administered to an injured nerve.  Previous studies have examined the effects of external beam radiation on nerve regeneration in rodents following either preoperative or postoperative radiation therapy.  However, in these studies, histomorphometric analysis was performed up to 8 month post-operatively.  Given the exceptional neuroregenerative capacity of rodents, significant differences in nerve regeneration may go undetected if nerves are evaluated at such distant post-operative time points, as even empty nerve conduits and untreated nerve allografts will eventually support robust nerve regeneration. 

Methods: Forty-eight Lewis rates were randomized to 3 groups corresponding to tibial nerve crush, transection and repair, or reconstruction with isografts.  Half of the animals in each of these 3 groups (n = 8 per group) underwent 10 Gy of external beam radiation to the site of nerve injury at 7 days post-operatively, while the remaining 8 animals in each group were not subjected to radiation and served as controls.  On post-operative day 28, all animals were evaluated for functional recovery by serial walking track analysis and were then harvested for peripheral nerve histomorphometry.

Results: No significant differences in nerve fiber number, neural density, neural debris, or fiber width were noted between the control and experimental groups (see table below).  There were also no significant differences in functional recovery (statistical significance set at p<0.05). 

Conclusion: External beam radiation had no discernible effect on nerve regeneration or functional recovery in the 3 rodent nerve injury models studied.  All assessments were made at time points suitable for detecting differences in nerve regeneration between groups. The absence of differences between irradiated and control groups suggests that administration of external beam radiation to fields containing injured peripheral nerve is unlikely to adversely affect functional outcomes.

                           Nerve Fiber Count Data              Percent Neural Tissue Data

	Irradiated	Controls	Irradiated	Controls
Cut & Repair	5312 ± 1205	4895 ± 1061	9.98 ± 3.95	8.10 ± 2.26
Isograft Repair	3150 ± 1329	3076 ± 810	3.52 ± 1.25	2.55 ± 1.33
Crush Injury	5965 ± 1196	5640 ± 732	18.7 ± 20.7	20.7 ± 5.15