Hideo Kawai, Marie lie Baudrimont, Vincent Travers, and Laurent Sedel

A COMPARATIVE EXPERIMENTAL STUDY OF VASCULARIZED AND NONVASCULARIZED

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NERVE GRAFTS ABSTRACT In order to compare vascularized and nonvascularized nerve grafts in a normal bed, 96 median nerve grafts were performed in rabbits. The median nerves were grafted in situ bilaterally, whether vascularized or nonvascularized. The length of the grafts was 2 cm, 4 cm, or 6 cm. A morphometric study was performed eight weeks and 24 weeks after the operation. No significant differences were found between vascularized and nonvascularized grafts at the same levels of nerve grafts. However, significant differences between vascularized and nonvascularized grafts were found for 4-cm and 6-cm grafts at eight weeks, and for 6-cm grafts at 24 weeks postoperatively, comparing the proximal normal nerve segments with the nerve segments distal to the nerve grafts.

Since Taylor1 first reported a free vascularized superficial radial nerve graft, this microsurgical technique has been used in clinical cases. It is still a matter of controversy whether or not a vascularized nerve graft is better than a nonvascularized nerve graft for nerve regeneration.2 Some authors have reported encouraging experimental results with vascularized nerve grafts.3"7 Clinical indications for this procedure include ischemic recipient beds, nerve repairs of large nerve gaps, and reconstruction with large nerve trunk grafts. The results of clinical applications have been reported to be better than those of conventional nerve grafts.8-12 However, blood flow in free nerve grafts reportedly started after 72 hr,13-15 followed by a greater blood flow to the nonvascularized nerve graft at four through six days, suggesting that during the initial two days after operation, there is a difference between vascularized and nonvascularized nerve grafts. Therefore, difficult and time-consuming vascularized nerve grafts may not be necessary for many clinical situa-

tions. 1617 In fact, if the vascularized nerve graft fails, it may be more detrimental for nerve regeneration than a conventional nerve graft. In clinical cases, it is very difficult to comparatively evaluate the functional results of vascularized and nonvascularized nerve grafts. It was therefore decided to determine whether or not vascularized nerve grafts present advantages over nonvascularized ones in a normal bed, with special reference to the nerve graft length.

MATERIALS AND METHODS The bilateral median nerves of 48 white rabbits weighing 2.0 kg to 2.8 kg were used. The entire median nerve lies along the brachial artery and is fed by it anywhere between the axilla and elbow. Consequently, this nerve could easily be removed, either vascularized

Department of Orthopaedic Surgery, Osaka University Medical School, Osaka, Japan, Orthopaedic Services, Hopital Saint-Antoine and Hopital Saint-Louis, and Central Service of Anatomy and Cytologic Pathology, Hopital Saint-Antoine, Paris, France Reprint requests-. Dr. Kawai, Dept. of Orthopaedic Surgery, Osaka University Medical School, 1-1-50 Fukushima, Fukushima-ku, Okasa 553, Japan Accepted for publication February 22, 1990 Copyright © 1990 by Thieme Medical Publishers, Inc., 381 Park Avenue South, New York, NY 10016. All rights reserved.

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JOURNAL OF RECONSTRUCTIVE MICROSURGERY/VOLUME 6, NUMBER 3

Figure 1. The right median nerve lying along the brachial artery was cut proximally and distally, leaving the connection between the median nerve and brachial artery, and sutured in situ. A vascularized 6-cm nerve graft 24 weeks postoperatively.

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Figure 2. The left median nerve was freed totally from the vascular supply and sutured in situ. A nonvascularized 4-cm nerve graft, eight weeks after surgery.

and 24 weeks after the procedure. The remaining 14 rabbits had died from pulmonary infections and were excluded. The histologic specimens at eight weeks were taken bilaterally at points 5 mm proximal and 5 mm distal to the nerve graft, and from the middle of the nerve graft. The histologic sections at 24 weeks were performed at points 5 mm proximal and 5 mm distal to the nerve graft. The specimens were fixed in 2.5 percent glutaraldehyde and stained with toluidine blue. A morphometric study of the transverse section was then performed. The diameter and number of myelinated fibers per mm2 were determined, with semiautomatic analyzer (Compaq) at x 1,000 magnification, measuring an eight times 1150 |xm2 area of the specimens.

RESULTS At eight weeks, the segment in the middle of the nerve graft, regardless of nerve-graft length, showed a significant increase in the number of axons over the nerve segment proximal to the nerve graft on both the vascularized and nonvascularized side. Furthermore, the segment distal to the nerve graft on the nonvascularized side showed statistically significantly fewer nerve fibers than did that proximal to it, except for the 2-cm nerve grafts (Table 1). At 24 weeks, the segment distal to the nerve graft of the 6-cm nerve graft showed significantly more axons than did the section proximal to it (Figs. 3 and 4), while differences in the number of axons between the nerve distal to the nerve graft segment and the nerve proximal to it on both the vascularized and nonvascularized sides of 2-cm and 4-cm nerve grafts and on the nonvascularized side of 6-cm grafts were not statistically significant (Table 2). Measurement of the myelinated axon diameter at eight weeks showed that the segment at the middle of the nerve graft had significantly smaller axons than the segment proximal to the nerve graft in 2-cm and 4-cm grafts, but this was not the case with 6-cm nerve grafts (Table 3). The nerve distal to the nerve graft segment showed a significantly smaller axon diameter than that proximal to it, bilaterally for 2-cm grafts and on the nonvascularized side of 4-cm grafts. However, this was not the case with 4-cm grafts on the vascularized side and 6-cm grafts on both sides. At 24 weeks, the segment distal to the nerve graft showed significantly smaller nerve axons on the vascularized side of 6-cm grafts but not on the bilateral sides of 2-cm and 4-cm grafts or on the nonvascularized side of 6-cm grafts (Table 4). To summarize, there was no difference in axon diameter or axon count between the vascularized and the nonvascularized side at the same levels of nerve segments. However, a comparison of the segment dis-

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or nonvascularized, without concern for the vascular pedicle to the nerve. Each animal was anesthetized with intramuscular ketamine (80 mg/kg) and chlorpromazine (2 mg/kg). The bilateral median nerves were exposed and identified without difficulty. The right median nerve was cut proximally at the axilla and distally at a level of the arm corresponding to the nerve graft length (2,4, or 6 cm), dissecting about 5 mm of nerve length to be cut and sutured. The right nerve was sutured in situ, leaving the vascular connection to the brachial artery throughout the nerve graft (Fig. 1). Each nerve suture was performed with two 10-0 nylon stitches under an operating microscope. The left median nerve was proximally and distally cut and completely freed, followed by microscopically performed nerve suture (Fig. 2). The operated limb was not immobilized after operation. The length of the nerve grafts was divided into three groups: 2 cm, 4 cm, and 6 cm. Thirty-four rabbits was sacrificed at eight weeks

JULY 1990

NERVE GRAFTS/KAWAI, BAUDRIMONT, TRAVERS, SEDEL Axon Counts at Eight Weeks* (per mm2)

Table I.

4-cm Nerve Craft

2-cm Nerve Craft VNG

VNGt

NVNG

7609 ± 2120 8 10787 ± 1889 10217 ± 2595 8 8 < 0.05 < 0.01 6535 ± 3139 5611 ± 2334 8 8 NS NS

Proximal No. Middle No. P Distal No. P

NVNGt

4956 ± 1112 6 10942 ± 2746 7826 ± 1627 6 6 < 0.01 < 0.01 4674 ± 2 5 1 6 2880 ± 866 6 6 NS < 0.01

b-cm Nerve Craft VNG

NVNG

5507 ±: 1040 3 12174 ± 1522 9348 ± 1522 2 2 < 0.01 < 0.01 3587 ± 1220 5109 ± 2367 3 3 NS < 0.05

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"Values represent mean ± standard error of mean. tVNG versus NVNG, p < 0.05. There are no statistical differences between VNG and NVNG for any other factors. p values represent the results of a statistical comparison between the segment proximal to the nerve graft and that distal to the nerve graft.t. VNG = vascularized nerve graft, NVNG = nonvascularized nerve graft, NS = not significant.

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Figure 4. Transverse section distal to the nonvascularized nerve segment of a 6-cm graft had fewer myelinated nerve fibers than that of a vascularized one at 24 weeks postoperatively (toluidine blue, xlOO).

Figure 3. Transverse section of vascularized nerve segment distal to a 6-cm nerve graft showed good myelinated nerve fibers 24 weeks postoperatively (toluidine blue, X100).

Table 2. 2-cm Nerve Craft VNG Proximal No. Distal No. p

Axon Counts at 24 Weeks* (per mm2)

NVNG

8139 ± 3121 6 9446 ± 3366 12018 ± 4069 5 6 NS NS

4-cm Nerve Craft VNG

NVNG

7601 ± 1996 6 7243 ± 1107 8031 ± 1655 6 6 NS NS

b-cm Nerve Craft VNG

NVNG

7652 ± 755 5 12217 ± 3424 9457 ± 3365 5 5 < 0.01 NS

*Values represent mean ± standard error of mean. p values represent the results of a statistical comparison between the segment proximal to the nerve graft and that distal to the nerve graft. VNG = vascularized nerve graft, NVNG = nonvascularized nerve graft, NS = not significant. There are no statistical differences between VNG and NVNG.

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JOURNAL OF RECONSTRUCTIVE MICROSURGERY/VOLUME 6, NUMBER 3 Table 3.

Axon Diameters at Eight Weeks* (per

2-cm Nerve Graft VNG

Proximal No. Middle No. P Distal No. P

4.04 < 3.42

A comparative experimental study of vascularized and nonvascularized nerve grafts.

In order to compare vascularized and nonvascularized nerve grafts in a normal bed, 96 median nerve grafts were performed in rabbits. The median nerves...
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