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Peripheral nerve injury repair using a nerve connector as an alternative to direct repair. OBJECTIVE: Nerve injuries can have devastating effects on patients' quality of life. However, the clinical results of direct nerve repair, which is commonly performed for peripheral nerve injury, are often unsatisfactory because of undesirable tension at the repair site. Previous studies have suggested that using a nerve conduit as a connector could provide outcomes that are equivalent to, or potentially better than, direct suture repair. Therefore, the aim of this study was to investigate the underlying mechanisms of peripheral nerve regeneration through a short gap encapsulated in a conduit using transgenic mice. METHODS: Sixty-four transgenic mice (Thy1 yellow fluorescent protein [YFP]-16), in which all axon fibers of the motor and sensory nerves constitutively express YFP, were used in this study. The sciatic nerve of each mouse underwent transection to artificially create an injury. Two weeks later, two types of repair operations were performed: 1) direct epineurial suture (direct repair [DR] group); and 2) repair using an artificial nerve (a polyglycolic acid conduit) as a nerve connector (connector repair [CR] group). Recovery was monitored by serial in vivo imaging of axonal growth and was assessed through histomorphometric measurements such as the axon number, myelinated fiber diameter, myelin sheath thickness, and g-ratio. Functional recovery was evaluated by calculating the area of anterior tibialis muscle fibers and using the von Frey filament test. Gene expression at the repair site was also analyzed. RESULTS: Although regeneration was slower in the CR than the DR group, the muscle area at week 6 was significantly higher in the CR group, indicating better motor recovery. Moreover, sensory recovery was similar between the CR and DR groups at the final 12-week examination. CONCLUSIONS: These findings indicate that repair using an artificial nerve as a connector achieved better, albeit slow, functional recovery than repair using a direct epineural suture.