Experimentelle Untersuchungen zur Heilung durchtrennter peripherer Nerven

Summary

The behavior of the connective tissue during the healing of transsected nerves was studied. Experiments were carried out with rahbits. The sciatic nerve was trans-sected and repaired using different techniques. Postoperatively the animals were all treated in exactly the same way. The clinical course was registrated carefully, with special attention to the return of the motor function and the occurence and extension of decubital ulcers. Finally the animals were sacrified, and the site of nerve repair was excised and histologically examined using Hämatoxilin, Eosin. Van Gieson, Kresylviolett, Klüver-Barriera, Sudan-Schwarz B, Bodian staining.

Two different techniques were compared by operating on the two sciatique nerves of the same animal. Individual factors could be excluded as the result of each two operations was compared in the same individual.

• A. In 32 rabbits, 64 sciatic nerves were repaired by epineural end-to-end suture (Mersilen 6×0) in order to study the timing of the healing process.

  • 1. After 3 days the circumference of the suture site was bridged by a fibrin membrane. Proliferation of connective tissue was seen mainly in the epineurium and the external layers of the perineurium for a short distance both proximal and distal to the suture line. The connective tissue advanced in the direction of the suture line. Obstacles were avoided by going round about on the external side.

    After 7 days a layer of connective tissue was formed at the circumference of the suture site. This layer originated from the epineurium proximal to the suture line, passed the sutures at their external side and reached the epineurium of the distal stump distal to the suture line.

    At the 3rd day the first regenerating axons were seen in the proximal stump. Some of them had reached the distal stump at day 7.

  • 2. After 14 days there was a firm connective tissue layer developed. There was fibrous tissue around the suture material. According to the tendency of the connective tissue to advance around the external site of obstacles, all the suture material was inside the connective tissue layer and shifted towards the center of the cross section.

  • 3. After 21 days there was progressive maturation of the connective tissue. Many regenerated axons had reached the distal stump. There was no tendency to aberration if the straight course of advancement was not blocked e.g. by suture material etc.

  • 4. After 5 weeks the perineurium was re-established. Between the two stumps there was a more-or-less broad endoneural scar. Many axons are to be seen within the distal stump having already crossed the suture line; some of them show thickening, loss of contour and fragmentation. As the remnants of the original axons following Wallerian degeneration had already disappeared within the 2nd week, these damaged axons are regenerated axons.

  • 5. After 2 months the scar formation is terminated.

• B. The influence of tension on the connective tissue proliferation. In 26 rabbits, a section of 5mm length (8%) was excised from the sciatic nerve and the two stumps united by end-to-end suture under moderate tension.

  The gap between the two stumps became filled by scar tissue, which was in these cases much wider. The connective tissue proliferation was increased. There was much more endoneural scar tissue formed, and the perineurium was thickened. Within the proximal and distal stump stretching of the nerve fibres and endoneural fibrosis was present. Many more of the regenerated axons within the distal stumps presented signs of degeneration.

  The forces which are needed to unite the stumps of a trans-sected nerve were determined.

  To unite the stumps of a nerve without any defect a force of 5–6 g is necessary. The force increases slowly as the defect increases up to 2 or 3 mm. If a larger defect is present the amount of tension necessary to unite the stumps increases rapidly (see Fig. 3).

  The functional result after suture under tension was much inferior to the controls (see Figs. 4 and 5).

  These experiments demonstrate the deterioration of the functional results if a nerve suture is carried out under tension. This corresponds to reports in the literature referring to interior clinical results if the size of nerve defects which are united by end-to-end suture exceed a certain limit.

  The reason for the inferior results is not only blocking of the suture line by scar tissue but to a certain degree secondary damage to regenerated axons, apparently by shrinkage of the scar tissue.

  In 10 human cases trans-sected peripheral nerves had been united by end-to-end suture under moderate tension 6–12 months previously. No function returned. Therefore the suture sites were resected and the nerve defects bridged by nerve grafts. The specimens were studied carefully. In all of them much scar tissue was found between the nerve stumps. Suture material with granulomatas could be seen within the cross sections. In 5 cases only a few axons were present in the distal stumps; in 3 cases a larger number were present. Many of them showed signs of recent damage. Since the primary nerve lesion 6–12 months had passed, and this proves that the damaged axons or regenerated axons having suffered secondary damage. The results of the experiments in rabbits are confirmed by this study in human specimens.

• C. By reducing the tension at the suture site connective tissue proliferation and scar formation could be reduced.

• D. In 32 rabbits a section 5 mm in length of one sciatic nerve was resected and regrafted into the defect as a free graft. In this experiment the regenerating axons had to cross two suture lines in the nerve and were under the same tension as in the case of end-to-end suture without a defect.

  In 25 rabbits the sciatic nerve was trans-sected. A nerve graft of 5 mm, provided from the contralateral sciatic nerve was introduced as a free graft. In this group the axons had to cross two suture lines, but the nerve was under reduced tension.

  In 3 rabbits the total gap between the nerve stumps due to retraction after trans-section (6–8 mm) was bridged by grafts. These nerves were under no tension at all.

  The connective tissue proliferation decreases with decreasing tension. The endoneural scars were very thin, and in cases with long grafts hardly to be detected.

  The functional results demonstrated that under favorable conditions the regeneration after grafting is equal to end-to-end suture, and much better than after end-to-end suture under tension (Figs. 4 and 5).

• E. Wrapping of the suture site by collagen, millipore or silastic membranes increased connective tissue proliferation between nerve and sheath. The functional results were inferior to simple suture.

• F. Suture material causes granulomatas and fibrosis. Due to the advancement of the connective tissue along the outer site of the sutures they are shifted towards the centre. Therefore in a part of the cross section the axon growth is impeded. The connective tissue proliferation is reduced if only a very small amount of very fine suture material is used.

  The use of cyanoacrylate glues lead to a high degree of fibrosis and inferior results.

  Homogenous and autogenous plasma was used by different authors, but severe reactions against fibrin and deviation of the growing axons was observed.

• G. Natural union. To reduce the operative trauma and to avoid any foreign body reaction nerve grafts were introduced into the gap resulting from retraction of the nerve stumps after trans-section without using any suture, glue or anything else to secure the union. The nerve stumps and the ends of the graft were united very carefully. As the graft was exactly as long as, or even a bit longer than, the gap, there was no tendency to separate. After 20 minutes the ends adhered strongly enough to permit the total nerve, including the graft, to be excised and removed without occurence of separation.

• H. From the experiments the conclusion was drawn that, when uniting peripheral nerves, tension should be avoided. If there is a defect, nerve grafts yield better results than suture under tension.

  The following points can be established.

  • 1. The origin of the main part of the connective tissue after trans-section of a peripheral nerve is the epineurium. Connective tissue proliferation of the surrounding connective tissue does not play any role if approximation of the stumps in secured.

  • 2. The circumference of the suture line is bridged by a fibrin membrane after 3 days and by a layer of connective tissue after 7 days.

  • 3. The amount of connective tissue proliferation depends of the tension at the suture line. It is secondarily affected by the operative trauma and by the amount and quality of the suture material. Wrapping does not decrease the connective tissue proliferation.

  • 4. Without obstacles such as scars and suture granulomatas the regenerating axons proceed straight ahead without any tendency to aberrate. Wrapping seems therefore not be of any advantage.

  • 5. The connective tissue proliferation can be decreased by: Avoiding tension. Reducing the operative trauma. Reducing amount of suture material. Resection of the epineurium as main source of the connective tissue proliferation.

  • 6. If approximation without tension is not possible, nerve grafting should be carried out.

On the basis of the experimental experience the following operative technique of nerve grafting was developed:

The epineurium of the two nerve stumps is resected. A dissection of the fasciculi of the nerve stumps is carried out. Major fasciculi are isolated individually. Minor fasciculi are isolated in groups of 3–5. The ends are resected at different levels according to the amount of trauma or fibrosis present. A sketch is made of the fascicular structure of the two nerve stumps. Using this sketch we try to define the corresponding fasciculi or groups of fasciculi. Between the corresponding fasciculi or groups of fasciculi nerve grafts (sural nerve) are introduced. The grafts are larger than the defect in position of function. Under microscopic control a careful adaptation is achieved. One suture (Nylon 10×0) at each end of each graft is used to secure the union. Under certain conditions we have relied only on the natural union and did not use any suture at all. As the fasciculi respectively groups of fasciculi had been resected at different levels, stumps and grafts are interdigitated with each other. For a median nerve 4–6, and for an ulnar nerve 3–5 individual nerve grafts were used.

This technique was used in more than 200 cases with satisfactory results. The results even after bridging long defects (more than 5 cm) are good, and much better than the results published by Asworth, Boyes and Stark (1971) who used end-to-end suture to overcome large defects of peripheral nerves.