Tensile strength of healing peripheral nerves

Although the time required for a nerve to gain sufficient strength to withstand normal physiologic forces of joint motion is unknown, typically nerve repairs are protected up to 3 weeks postoperatively. The authors investigated the mechanical strength of a nerve repair as a function of time. Fifty adult Sprague-Dawley rats underwent sciatic nerve division and repair, and were sacrificed in groups of 10 at 0, 1, 2, 4, and 8 weeks. Repaired nerves were then mechanically loaded at 5 mm/min to failure. Gapping across the repair site was captured on high-resolution video. The contralateral sciatic nerve served as a control. A significant increase in tensile strength was gained between 0 and 1 week and between 2 and 4 weeks. Healing nerves achieved 63 percent of the strength of the control by 8 weeks. Controls showed no gain in strength over the testing period. Gapping occurred at lower forces at all time increments. From 0 to 1 week, a significant increase in load necessary to produce gapping was found, which did not increase significantly again until 8 weeks. These results may have implications for postoperative rehabilitation protocols in patients with nerve injuries.