Loop nerve graft prefabrication for peripheral nerve defect reconstruction

Abstract

Background: Delayed autologous nerve graft reconstruction is inevitable in devastating injuries. Delayed or prolonged repair time has deleterious effects on nerve grafts. We aimed improving and accelerating nerve graft reconstruction process in a rat long nerve defect model with loop nerve graft prefabrication particularly to utilize for injuries with tissue loss.

Methods: Twenty-four Sprague-Dawley rats were allocated into three groups. 1.5 cm long peroneal nerve segment was excised, reversed in orientation, and used as autologous nerve graft. In conventional interpositional nerve graft group (Group 1), nerve defects were repaired in single-stage. In loop nerve graft prefabrication group (Group 2), grafts were sutured end-to-end (ETE) to the proximal peroneal nerve stumps. Distal ends of the grafts were sutured end-to-side to the peroneal nerve stumps 5 mm proximal to the ETE repair sites in first stage. In second stage, distal ends of the prefabricated grafts were transposed and sutured to distal nerve stumps. In staged conventional interpositional nerve graft group (Group 3), grafts were sutured ETE to proximal peroneal nerve stumps in first stage. Distal ends of the grafts and nerve stumps were tacked to the surrounding muscles until the final repair in second stage. Follow-up period was 4 weeks for each stage in Groups 2 and 3, and 8 weeks for Group 1. Peroneal function index (PFI), electrophysiology, and histological assessments were conducted after 8 weeks. P<0.05 was considered significant for statistical analysis.

Results: PFI results of Group 1 (-22.75±5.76) and 2 (-22.08±6) did not show statistical difference (p>0.05). Group 3 (-33.64±6.4) had a statistical difference compared to other groups (p<0.05). Electrophysiology results of Group 1 (16.19±2.15 mV/1.16±0.21 ms) and 2 (15.95±2.82 mV/1.17±0.16 ms) did not present statistical difference (p>0.05), whereas both groups had a statistical difference compared to Group 3 (10.44±1.96 mV/1.51±0.15 ms) (p<0.05). Axon counts of Group 1 (2227±260.4) and 3 (2194±201.1) did not have statistical difference (p>0.05), whereas both groups had significantly poor axon counts compared to Group 2 (2531±91.18) (p<0.05).

Conclusion: Loop nerve graft prefabrication improved axonal regeneration without delay. Loop prefabrication can accelerate prolonged regeneration time for the injuries indicating a delayed nerve reconstruction. Higher axon counts derived with loop nerve prefabrication may even foster its investigation in immediate long nerve defect reconstructions in further studies.

Figure 1

Peroneal nerve segment excised and reversed as a conventional interpositional autologous nerve graft (a), nerve defect repaired with conventional interpositional autologous nerve graft (b), and schematic illustration for the single stage conventional interpositional nerve graft repair (c).

Figure 2

Epineurotomy with delicate axotomy for end-to-side coaptation.

Figure 3

First stage of loop peroneal nerve graft prefabrication with end-to-end and end-to-side coaptation (a). Schematic illustration for first stage of loop peroneal nerve graft prefabrication. Blue arrows indicate the end-to-side axonal sprouting to the distal end of the nerve graft. Red arrows represent the end-to-end axonal sprouting to the proximal end of the nerve graft (b). End-to-side coaptation is transected and the distal end of the nerve graft is transposed to the distal nerve stump in second stage (c). Schematic illustration for second stage of the loop nerve graft prefabrication. Red arrow indicates the regular pathway for the axonal regeneration. Blue arrow indicates the axonal sprouting from the end-to-side coaptation site that regenerated and refreshed the distal end of the nerve graft. The reverse axonal sprouting direction observed at the distal end of the nerve graft is consistent with reversing the nerve graft orientation after the harvest (d).

Figure 4

Staged conventional interpositional nerve graft repair. In first stage, proximal end of the nerve graft is coaptated to the proximal nerve stump. Distal end of the graft and distal nerve stump is not coaptated (a). Schematic illustration of the staged interpositional nerve grafting. The red arrow shows the axonal sprouting direction (b). In second stage, distal end of the nerve graft and distal nerve stump are coaptated (c). The red arrow in the illustration shows the constant regeneration pathway in conventional nerve graft repair (d).

Figure 5

Peroneal function index (PFI) scores.

Figure 6

Nerve conduction study amplitude results.

Figure 7

Nerve conduction study velocity results.

Figure 8

Light (a-c) and electron (d-f) micrographs. (a) Conventional single stage interpositional nerve graft repair group. Black arrow: Myelinated nerve fiber, arrowhead: Schwann cell, asterisk: connective tissue, white arrow: Fibroblast. (b) Loop peroneal nerve graft prefabrication group. Black arrow: Myelinated nerve fiber, arrowhead: Schwann cell, asterisk: connective tissue. (c) Staged interpositional nerve graft repair group. Black arrow: Myelinated nerve fiber, arrowhead: Schwann cell, asterisk: connective tissue, white arrow: fibroblast. (d) Conventional single stage interpositional nerve graft repair group; a: axoplasm, m: myelin sheath, n: nucleus of Schwann cell, Sc: cytoplasm of Schwann cell. (e) Loop peroneal nerve graft prefabrication group; a: axoplasm, m: myelin sheath, Sc: cytoplasm of Schwann cell, c: collagen fibers, asterisk: vacuole in the axoplasm. (f) Staged interpositional nerve graft repair group; a: axoplasm, m: myelin sheath, Sc: cytoplasm of Schwann cell, n: nucleus of Schwann cell, asterisk: vacuole in the axoplasm.

Figure 9

Myelinated axon count results.