Tensile properties of the neurorrhaphy site in the rat sciatic nerve

Forty-three epineurial rat sciatic neurorrhaphies were performed to gain insight into the duration necessary to protect a nerve repair. By killing animals at varying intervals after neurorrhaphy and harvesting the sciatic nerves, we investigated the timing of neurorrhaphy site tensile property recovery. There were 9 normal control nerves. No nerves ruptured after repair, even though the operated legs were not immobilized. Ultimate and maximal simulated in situ loads and elongations were measured, and stresses and strains were calculated from mechanical testing. Sixty-four percent of normal ultimate stress was gained during the first week after neurorrhaphy, with no significant increase for 10 to 12 weeks. Ultimate strains for control and repaired nerves for all time intervals ranged from 14.2% +/- 1.8% to 26.0% +/- 3.9%. Maximal simulated in situ stress and strain remained in the toe region of the stress versus strain curve, implying that no nerves ruptured because ultimate stress and strain were never approached. Caution must be exercised in extrapolating these data to the human clinical situation.