Management of peripheral nerve defects: external fixator-assisted primary neurorrhaphy

Controlled joint extension followed by gradual distraction with use of an external fixator may facilitate primary repair of peripheral nerve defects by permitting end-to-end repair without tension. The hypothesis of the present study was that gradual lengthening of nerve repairs with use of incremental distraction would provide superior results compared with grafting or repair under tension.

A median nerve segment measuring four times the diameter of the nerve was resected in thirty-six rabbits to create a 7-mm gap in the nerve. Neurorrhaphy was performed with use of one of three techniques. In Group 1 (cable graft), a tension-free medial antebrachial cutaneous graft was placed to allow full range of motion of the elbow postoperatively. In Group 2 (end-to-end repair without distraction), the elbow was externally fixed in hyperflexion and the nerve was repaired end-to-end. At fourteen days, the fixator was removed and unprotected elbow motion was permitted. In Group 3 (end-to-end repair with gradual distraction), the elbow was externally fixed in hyperflexion and primary neurorrhaphy was performed. At fourteen days, the elbow was extended 10 degrees every other day with use of the articulated external fixator until full extension was achieved. Median nerve amplitude, latency, and nerve-conduction velocity; flexor digitorum superficialis single-twitch force generation and maximum tetanic force generation; muscle mass; and elbow range of motion were measured at three or six months. In addition, histologic analysis of the median nerve distal to the repair site and the morphometry of the neuromuscular junction in the flexor digitorum superficialis were performed at six months.

All rabbits regained full active and passive range of motion. At three months, the nerve-conduction velocities in Groups 2 and 3 were significantly greater than that in Group 1. At six months, the nerve-conduction velocities and amplitudes in Group 3 were significantly greater than those in Groups 1 and 2. At six months, the tetanic force in Group 3 was significantly greater than those in Groups 1 and 2. There were no significant differences in muscle mass among the groups. There were no significant differences in histological findings among the three groups, although there was a trend toward larger fiber size in Group 3 as compared with the other two groups. The neuromuscular junctions in Group 3 had a significantly larger surface area than did those in Group 1 (p = 0.002) and Group 2 (p = 0.034).

The use of an articulated external fixator and controlled gradual distraction appears to facilitate the treatment of peripheral nerve defects.