Type grouping in rat skeletal muscle after crush injury

Laboratory investigation

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Accuracy of reinnervation is an important factor that determines outcome after nerve injury and repair. Type grouping—the clustering of muscle fibers of the same type after reinnervation—can be used to investigate the accuracy of reinnervation. In this study, the degree of type grouping after crush injury in rats was compared with the clustering of muscle fibers after autografting or single-lumen nerve grafting.


Twelve weeks after sciatic nerve crush injury in rats, clustering of Type I muscle fibers was analyzed in the target muscle with adenosine 5′-triphosphatase staining. In addition, the number of regenerated axons was determined in the nerve distal to the crush injury. Results were compared with that of the authors' previous study.


Type grouping was more abundant after crush injury than after autograft or single-lumen nerve graft repair.


Crush injury leads to more clustered innervation of muscle fibers, probably because the Schwann cell basal lamina tubes are not interrupted as they are in autograft or artificial nerve graft repair. This finding adds to understanding the processes playing a role in nerve regeneration.

Abbreviations used in this paper: CSA = cross-sectional area; TMC = trimethylene carbonate.

Article Information

Drs. Bovenberg and Degeling contributed equally to this study.

Address correspondence to: Carmen L. A. M. Vleggeert-Lankamp, Ph.D., M.D., Department of Neurosurgery, Leiden University Medical Centre, P.O. Box 9600, RC Leiden, The Netherlands NL-2300. email: cvleggeert@lumc.nl.

Please include this information when citing this paper: published online November 26, 2010; DOI: 10.3171/2010.9.JNS091656.

© AANS, except where prohibited by US copyright law.



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    Light microscopic cross-sections and diameter frequency distributions of the peroneal nerve of unoperated (control) and experimental nerves. Left column: Light microscopy transverse 1-μm cross-sections of peroneal nerves, immersion fixed, and stained with a 1% toluidine blue/1% borax solution. The regenerated peroneal nerves had the same thickness as the control nerve, and appeared healthy. Center column: Enlarged samples of the depicted cross-sections, their position indicated by the inset squares in the left column. The diameter of the regenerated nerve fibers was smaller compared with control nerve fibers, and the myelin sheath was thinner. Often multiple fibers were fasciculated within areas of size comparable to the size of single myelinated fibers in the control nerve. Right column: Bar graphs demonstrating fiber diameter frequency distributions. For each graph the data were lumped into 28 diameter classes (bin size 0.5 μm), and plotted against the number of nerve fibers present in that class. A general decrease in the diameter range of all regenerating nerve fibers is evident.

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    Nerve morphometric data of control (4 animals), autograft (12 animals), TMC graft (5 animals), and crush (6 animals) nerves are depicted as bar graphs. A: Total surface of the nerve cross-section (nerve area). B: Mean diameter of myelinated nerve fibers. C: Number of myelinated nerve fibers. D: Density of myelinated nerve fibers. Data are represented as mean ± SD. *Significant difference compared with control group; #significant difference compared with autograft group.

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    Light microscopy cross-sections of gastrocnemius muscle sections. Transverse 1-μm cross-sections of gastrocnemius muscles distal to unoperated (A) and crushed (B) peroneal nerves, immersion fixed, and adenosine 5′-triphosphatase stained.

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    Muscle morphometrical data of control (4 animals), autograft (12 animals), TMC graft (5 animals), and crush (6 animals) gastrocnemius muscles are depicted as bar graphs. A: Muscle CSA. B: Mean muscle fiber CSA. C: Total number of muscle fibers. D: Mean Type I (light gray bar) and Type II (dark gray bar) muscle fiber numbers. E: Mean Type I and Type II muscle fiber CSA. *Significant difference compared with control group.

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    Type grouping in gastrocnemius muscle. A: Bar graph demonstrating type grouping percentages. The type grouping percentage represents the number of clustered Type I fibers present in the gastrocnemius muscle, and does not take into account the size of the clusters. Data are represented as means ± SDs. *Significantly different compared with control muscle; #significantly different compared with autograft muscle; $significantly different compared with TMC graft muscle. B–E: Pie charts demonstrating the distribution of Type I cluster sizes (grouped) in gastrocnemius muscle. Percentage frequency of occurrence of Type I cluster sizes 1 (gray), 2–12 (black), and > 12 (white) in the control, autograft, crush, and TMC graft groups. Crush resulted in the lowest percentage of size 1 fiber clusters (unclustered fibers), and the highest percentage of both 2–12 and > 12 fiber clusters, followed by autograft.


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