Limitations of conduits in peripheral nerve repairs

Abstract

Nerve conduits have emerged as alternatives to autologous nerve grafts, but their use in large-diameter nerve deficits remains untested. We report four patients who underwent repair of large-diameter nerves using absorbable nerve conduits and discuss the failed clinical outcomes. The reported cases demonstrate the importance of evaluating the length, diameter, and function of nerves undergoing conduit repair. In large-diameter nerves, the use of conduits should be carefully considered.

Figure 1

Patient 1—intraoperative photos. a Four years after right median nerve repair with a collagen conduit; this intraoperative view revealed a large neuroma-in-continuity. b A 7-cm gap was developed before normal fascicular pattern was discovered, and c the defect was then repaired using the medial antebrachial cutaneous nerve.

Figure 2

Patient 1—histologic specimens. a Histology of the surgical specimen reveals dense fibrinous scar tissue and lack of nerve structures in the section of the distal conduit. b The midconduit section shows significant disorganized architecture with no axonal organization, consistent with neuroma. c Proximally, normal nerve architecture is demonstrated.

Figure 3

Patient 2—intraoperative photos. a Proximal stump (P) ending in a large neuroma discontinuous with distal stump (D) and adjacent to scar tissue on the radial aspect (XX, separated by dashed line), 9 months postinjury. b Trimming of the nerve stumps resulted in a 6-cm gap distance. c Four separate medial antebrachial cutaneous nerve channels were used to bridge the gap.

Figure 4

Patient 2—histologic specimens. a Histology of the surgical specimen reveals dense fibrinous scar tissue and lack of nerve structures in the section of the distal conduit. b The proximal conduit section shows significant disorganized architecture with no axonal organization, consistent with neuroma. No regeneration was seen through the conduit. c Proximally, normal nerve architecture is demonstrated.

Figure 5

Comparative study findings. A study comparing collagen conduits, processed allografts, and isografts yielded the distal fiber counts illustrated at a 6-week time point. No distal nerve regeneration was demonstrated in the conduit and processed allograft animals when the gap length was doubled [24].

Figure 6

Large-diameter nerves. The figure illustrates the importance of diameter in determining overall volume of a nerve gap. Conduits A and B are of equal volume. Doubling the radius in conduit B gives an equal total volume of conduit A with only one-fourth the length according to the formula V = Πr²L where V is the volume, r is the radius, Π is the pi (∼3.14), and L is the length.