J Korean Neurosurg Soc.  2016 Sep;59(5):430-436. 10.3340/jkns.2016.59.5.430.

Chronic Paraspinal Muscle Injury Model in Rat

• Cho TG
• Park SW
• Kim YB

• KMID: 2351709
• DOI: http://doi.org/10.3340/jkns.2016.59.5.430

Abstract

OBJECTIVE
The objective of this study is to establish an animal model of chronic paraspinal muscle injury in rat.
METHODS
Fifty four Sprague-Dawley male rats were divided into experimental group (n=30), sham (n=15), and normal group (n=9). Incision was done from T7 to L2 and paraspinal muscles were detached from spine and tied at each level. The paraspinal muscles were exposed and untied at 2 weeks after surgery. Sham operation was done by paraspinal muscles dissection at the same levels and wound closure was done without tying. Kyphotic index and thoracolumbar Cobb's angle were measured at preoperative, 2, 4, 8, and 12 weeks after the first surgery for all groups. The rats were sacrificed at 4, 8, and 12 weeks after the first surgery, and performed histological examinations.
RESULTS
At 4 weeks after surgery, the kyphotic index decreased, but, Cobb's angle increased significantly in the experimental group (p<0.05), and then that were maintained until the end of the experiment. However, there were no significant differences of the kyphotic index and Cobb's angle between sham and normal groups. In histological examinations, necrosis and fibrosis were observed definitely and persisted until 12 weeks after surgery. There were also presences of regenerated muscle cells which nucleus is at the center of cytoplasm, centronucleated myofibers.
CONCLUSION
Our chronic injury model of paraspinal muscles in rats shows necrosis and fibrosis in the muscles for 12 weeks after surgery, which might be useful to study the pathophysiology of the degenerative thoracolumbar kyphosis or degeneration of paraspinal muscles.

Keyword

Animal model; Paraspinal muscle; Chronic injury; Kyphosis; Degeneration

MeSH Terms

Animals
Cytoplasm
Fibrosis
Humans
Kyphosis
Male
Models, Animal
Muscle Cells
Muscles
Necrosis
Paraspinal Muscles*
Rats*
Rats, Sprague-Dawley
Spine
Wounds and Injuries

Figure

• 

  Fig. 1 Incision was done from T7 to L2. Paraspinal muscles were detached from the spinous processes, facet joints and transverse processes (A). The Fig. of confirming the paraspinal muscles though Adson forcep (B). Tied both muscles eight respectively at each intervertebral level with black silk 4-0 (Ethicon) (C). Two weeks after the surgery, paraspinal muscle exposed (D) and untied.

• 

  Fig. 2 Representative lateral radiographs of an experimental rat model with C-arm. Preoperative image (A) and the image after 12 weeks of the surgery (B). The kyphotic deformity at 12 weeks after the surgery increased compared to preopearive image.

• 

  Fig. 3 Kyphotic index was calculated as the ratio of length to depth of the thoracodorsal kyphosis (length/depth). Length was measured as the linear distance from the ventral surface of the vertebral bodies of C7 to L6. Depth was measured as the maximum perpendicular distance from that line to the dorsal vertebral border.

• 

  Fig. 4 Kyphotic index decreased significantly at 2 weeks after surgery comparing to preoperative index, and at 4 weeks after surgery comparing to the index at 2 weeks after surgery. All the kyphotic indices of experimental group at 2, 4, 8, and 12 weeks after surgery were smaller significantly comparing to those of sham and normal groups at the corresponding time points. *Significant difference between the experimental and sham groups (p<0.05), †Significant difference in experimental group between preoperative and POD#2 week (p<0.05), ‡Significant difference in experimental group between POD#2 week and POD#4 week (p<0.05). POD : post-operative day.

• 

  Fig. 5 Cobb's angle increased significantly at 2 weeks comparing to preoperative index, and the angle also increased significantly at 4 weeks comparing to that of 2 weeks. There was no significant change in the angles between 4 and 12 weeks after surgery. All the Cobb's angles of experimental group at 2, 4, 8, and 12 weeks after surgery were greater significantly comparing to the corresponding angles of sham and normal groups. *Significant difference between the experimental and sham groups (p<0.05), †Significant difference in experimental group between preoperative and POD#2 week (p<0.05), ‡Significant difference in experimental group between POD#2 week and POD#4 week (p<0.05). POD : post-operative day.

• 

  Fig. 6 The distribution of muscle fibers in the sham group is regular. Hematoxylin and eosin (H&E), ×100 (A), Picrosirius red, ×100 (B).

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  Fig. 7 In the experimental group at four weeks after the surgery, the fibers with necrosis (*) and inflammatory cells infiltrations are visible [hematoxylin and eosin (H&E), ×100, A]. Connective tissue proliferation and segmental fibrosis are observed (Picrosirius red, ×100, B).

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  Fig. 8 In the experimental group at eight weeks after the surgery, inflammatory cells and necrotic fibers are decreased and connective tissue proliferation and segmental fibrosis are increased by comparison with findings at four weeks after the surgery. The forms of the muscle fibers are irregular and the centronucleated myofibers (arrow) are observed [A : Hematoxylin and eosin (H&E), ×100; B : Picrosirius red ×100; C : Picrosirius red ×400]. In the experimental group at twelve weeks after the surgery, similar findings are observed (D : H&E, ×100; E : Picrosirius red ×100; F : Picrosirius red ×400).

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