Effect of conduit repair on aberrant motor axon growth within the nerve graft in rats

After peripheral nerve injury, minimizing axonal misdirection has been a matter of importance to obtain good functional outcomes. In general, it becomes more challenging as the nerve defect length is longer. As previous works suggested that a conduit repair leaving a short gap could induce some target-specific reservation, we expected that a distally placed conduit combined with nerve graft would enhance the specificity of reservation, especially in dealing with a long gap. To test this, a 14-mm-long gap was created in the rat sciatic nerves and repaired with either 1) whole nerve graft (WG), 2) interfascicular nerve grafts (FG), or 3) whole nerve graft combined with distally placed silicone tube leaving a 5-mm gap (TUBG). At the end of follow up, the extent of target specific reservation (measurement of the compound muscle action potentials evoked by stimulation of the sciatic nerve and its tibial and common peroneal fascicles) and the accuracy of motoneuronal projection (sequential retrograde labeling of the common peroneal motor pool) were assessed. Both assessments revealed that groups FG and TUBG had a similar selectivity, which was significantly higher than in group WG. Consistent with these results, the functional recovery as assessed by walking track analysis showed no significant difference between groups FG and TUBG, whereas those were significantly superior to group WG. In contrast, histomorphometric assessment of the regenerating axons and wet muscle weight showed no significant difference among the three groups. In conclusion, conduit repair would have some effects on reducing motor axonal misdirection, and it might be more effective when used in the management of a large defect in combination with nerve graft.