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 Table of Contents  
ORIGINAL ARTICLE
Year : 2019  |  Volume : 2  |  Issue : 2  |  Page : 134-137

Lateral Approach to the Lumbar Spine of Sprague Dawley Rat: Development of a Novel Animal Model for Spine Surgery


1 Indian Spinal Injuries Centre, New Delhi, India
2 National Institute of Immunology, New Delhi, India

Date of Web Publication23-Jul-2019

Correspondence Address:
Dr. Harvinder Singh Chhabra
Indian Spinal Injuries Centre, Vasant Kunj, New Delhi - 110 070
India
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Source of Support: None, Conflict of Interest: None


DOI: 10.4103/isj.isj_59_18

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  Abstract 


Background: Low back pain is a common ailment affecting individuals all around the globe. Animal models are required to study and further explore the treatment modalities. Lumbar spinal surgeries and disc repair is an important tissue engineering research domain. Dorsal and ventral approaches to access rat spine have been traditionally performed but suffer from a number of shortcomings such as higher morbidity, loss of neurology, high postoperative pain, and longer surgery. Methods: We used ten male Sprague Dawly rats, 3 months of age, and weighing an average of 280 gm. The surgeries were performed under dissociative anesthesia (ketamine: 50 mg/kg body weight). The spine was approached by left lateral incision extending from iliac crest and centering the level to be exposed. Skin and subcutaneous tissues were cut, external and internal oblique muscles were split in the direction of fibers, transverse abdominis was split vertically, and psoas was sacrificed. This made the spine and disc levels visible from the left lateral aspect. The muscles were approximated, and skin was closed with nonabsorbable mattress sutures. Postoperative analgesics (meloxicam 5 mg/kg body weight) and antibiotics (ceftriaxone 30 mg/kg body weight) were used. Results: This work has led to the development of a novel in vivo rat model using lateral retroperitoneal approach. This approach provides less pain and faster recovery in the postoperative stage. Moreover, it allows easy exposure and little surgery-related peri- or post-operative complications. Conclusion: Lateral retroperitoneal approach is a novel and safe method of spinal exposure in rats which may pave way for various live rat spine surgery models and experiments in future.

Keywords: Animal morbidity, lateral approach, spine model, Sprague Dawley rat


How to cite this article:
Goel SA, Nagpal P, Nagarajan P, Panda A K, Chhabra HS. Lateral Approach to the Lumbar Spine of Sprague Dawley Rat: Development of a Novel Animal Model for Spine Surgery. Indian Spine J 2019;2:134-7

How to cite this URL:
Goel SA, Nagpal P, Nagarajan P, Panda A K, Chhabra HS. Lateral Approach to the Lumbar Spine of Sprague Dawley Rat: Development of a Novel Animal Model for Spine Surgery. Indian Spine J [serial online] 2019 [cited 2019 Dec 13];2:134-7. Available from: http://www.isjonline.com/text.asp?2019/2/2/134/263284




  Introduction Top


Low back pain is a common ailment affecting individuals around the globe.[1] As per a recent study, majority of hours lost during work is due to low back pain.[2],[3],[4],[5],[6] Since progressive degenerative changes of the intervertebral discs are age and posture related, these numbers will probably continue to increase as the population grows older.[7]

Researchers have used animal models to study the mechanism of lumbar disc diseases in variousin vivo studies such as rabbit, sheep, goat, pig, and dog.[8],[9],[10],[11],[12] There even have been use ofin vivo models of disc diseases for studying tissue engineering techniques such as gene transfer, local hormonal injection, and autologous cell implantation.[1],[13] Newer modalities and techniques need to be developed to tackle the situation of ease of accessibility, reproducibility with less pain, and morbidity to the animal. Hence, it is important to develop animal models and surgical techniques to study the approaches to the animal spine with minimum harm. A few animal models do exist to study operative techniques and treatment modalities. Dorsal and ventral approaches to rat spine have been published in literature but suffer from a number of disadvantages.[14]

In this study, we have developed a rat surgery model where the approach was from lateral aspect. This helped in avoiding the damage to the intraperitoneal organs, reduced pain in postoperative period, reduced surgical time, and kept the surgeon away from the vessels such as aorta and vena cava, thus limiting animal fatality. Moreover, targeting the spine from the lateral area gave access to the body of the spine. This even helped to preserve the neurology of rat by reducing the chances of nerve injury.

Technique

We used 10 male Sprague Dawly rats, 3 months of age, and weighing an average of 280 g. The surgeries were conducted after ethical board approval and IRB approval from National Institute of Immunology (where the experiments were performed) and as per the current ethical norms.

Anesthesia

A single intraperitoneal injection of 50 mg/kg ketamine and 10 mg/kg xylazine was used to anaesthetize the rats. Ophthalmic ointment was used to prevent eye dehydration. This method of anesthesia has been widely used to anesthetize the experimental animals.[14]

Positioning

After shaving and disinfecting the lateral aspect of the abdomen with 10% iodine solution followed by 70% isopropyl alcohol, the rats were placed in lateral position on heating pad [Figure 1]. The abdominal contents were allowed to hang, and the surgeon faced the anterior abdominal area [Figure 1]. The limbs were taped to the table. Surgery took place under strict aseptic precautions.
Figure 1: (a) Surgical table used during the lateral approach of rat surgery. (b) Rat positioning during surgery. The surgeon faces the abdominal area. Ic: Level of iliac crest, In: Tentative incision line, Ab: Loosely hanging abdomen

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Surgical approach

A curvilinear incision was made in the lateral abdominal wall [Figure 2]a. The incision was made on the left side of the rat abdomen. Skin and subcutaneous tissue were meticulously dissected. External oblique (EO) was dissected in the direction of the fibers [Figure 2]b. The internal oblique muscle was found perpendicular to EO in the area just below it [Figure 2]c. It was dissected in the direction of the fibers. Transverse abdominis was encountered next, and it was split vertically. Below the transverse abdominis muscle, there was peritoneal cavity which was not disturbed. The abdominal cavity was allowed to hang along with the abdominal contents. The spine was traced and psoas was sacrificed since the psoas muscle does not host lumbar plexus as in humans [Figure 2]d. The spine was visible from the lateral aspect without encountering any vessels/nerves or disturbing any vital organs [Figure 2]d and [Figure 3]a. The muscles were approximated, and the skin was closed with nonabsorbable vertical mattress sutures [Figure 3]b.
Figure 2: (a) Position of the rat on surgical table showing the dorsal (d) and ventral (v) area. (b) Fibers of external oblique muscle. Arrow shows the direction of the fibers. (c) Fibers of internal oblique muscle. Arrow shows the direction of the fibers. (d) Exposure of the spine (Sp). P: Psoas muscle

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Figure 3: (a) Exposure of the spine and L1 vertebral body. (b) After final closure and suturing of the wound

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Postoperative care

After surgery, oral meloxicam (5 mg/kg) was given and repeated every 12 hourly for 72 h to control pain. Injection ceftriaxone (30 mg/kg) was given 12 hourly for 3 days to prevent postoperative infections. Food access remained unrestricted during the postoperative period.


  Discussion Top


Dorsal and ventral approaches have been described in the past to approach the animal spine; however, they suffer from a number of short comings.[14],[15] Dorsal approach is the simplest of the technique as it does not involve vital organs.[15] However, it suffers with the limitations of exposing the rat discs or the anterior spinal structures completely. To reach the anterior structures with dorsal approach, the spine needs to be fractured or the rat needs to be sacrificed.[15] Moreover, this technique leads to neurological damage in rat models due to the difficulty in approaching anterior structures through fractured spine.[15] Ventral approach has been published in 2004 which discusses about targeting the anterior structures of rat spine.[14] However, the issue with such an approach is that it involves damage to the peritoneum and retraction of the vital organs, which may prove to be fatal.[14] Moreover, aorta and vena cava are encountered just in front of the spine; damage to them may lead to the death of the experimental animal. To add to it, since the organs in ventral area of rat have higher pain receptors, the animal suffers with more pain in postoperative stage.

The lateral approach to rat spine has been successfully conducted by us in 10 rats. The advantages of this technique include adequate exposure, simpler approach than dorsal/anterior to access discs, anterior spinal structures, and a reliable surgery. This procedure can be done by a single person in <40 min. No special microsurgical skills are required in this technique.

When compared with the ventral approach to spine,[14] there is no damage to the peritoneum, thus reducing the chances of morbidity and mortality in rats. The postoperative pain is also less as the vital organs and peritoneum are not disturbed. The inner layers need not be sutured as it involves only splitting of the muscles. These muscles can be approximated and skin sutured with nonabsorbable sutures. Neurological damage was not noted in any of our operated rats. Ventral approach has shown the complications of bleeding from prevertebral vessels.[14] These vessels were not encountered during the lateral approach. Aorta and vena cava were also left undisturbed during the lateral approach to the spine from the left side. There were no signs that the digestive tract suffered from excess retraction during the procedure. All rats had normal bowel and bladder control even in the postoperative stage. There is absence of peritoneal fixation of the intestine to the dorsal abdominal wall in rats.[14] This makes the exposure of the main portion of the lumbar spine easier in rats using anterior transperitoneal approach. This feature is not noted in humans, and hence, anterior transperitoneal approach has been considered inappropriate above the lumbosacral junction.[14],[15] The lateral approach may hold promise of being used in other animals too above the lumbosacral junction. This approach does suffer from a few limitations which need to be considered before planning an experiment. Approaching the L5–S1 junction is difficult due to the presence of high rising iliac crest. Hence, the extent of vertebral exposure is limited to L1–L4. Furthermore, the lumbar plexus in rats is formed by fourth lumbar to third sacral nerve and supplies the skin and muscles of pelvis and hind limbs. It lies deep within the abdominal cavity and should not be dissected lest it results in loss of neurology.

The feasibility of doing a diaphragm-splitting approach may be explored in future to reach the thoracic region. The surgeon may witness a few common issues during the surgery such as damage to the rat peritoneum, inadequate exposure, and limited space to work on discs. These may be resolved through the process of allowing the peritoneal contents to hang anteriorly and the use of high magnification microscope/loops.

Since we did not encounter any postoperative infections and little antibiotics were administered to the rats, we believe that aseptic surgery conditions are worthwhile in the procedure. All our surgeries included autoclaved instruments, disposable gloves and scalpel and fumigated rooms before surgery. All procedures, including intraperitoneal injection of ketamine, were done under strict aseptic precautions.


  Conclusion Top


The lateral approach to lumbar spine is surprisingly simple, safe, relatively painless, and reliable method for gaining access to the lumbar spine in the rat. The reproducibility of this technique may contribute to the usefulness of rodent models for variousin vivo studies of tissue engineering.

Financial support and sponsorship

Nil.

Conflicts of interest

There are no conflicts of interest.



 
  References Top

1.
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Boos N, Weissbach S, Rohrbach H, Weiler C, Spratt KF, Nerlich AG, et al. Classification of age-related changes in lumbar intervertebral discs: 2002 Volvo award in basic science. Spine (Phila Pa 1976) 2002;27:2631-44.  Back to cited text no. 7
    
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Lipson SJ, Muir H. 1980 Volvo award in basic science. Proteoglycans in experimental intervertebral disc degeneration. Spine (Phila Pa 1976) 1981;6:194-210.  Back to cited text no. 8
    
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Osti OL, Vernon-Roberts B, Fraser RD. 1990 Volvo award in experimental studies. Anulus tears and intervertebral disc degeneration. An experimental study using an animal model. Spine (Phila Pa 1976) 1990;15:762-7.  Back to cited text no. 9
    
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Kääpä E, Holm S, Han X, Takala T, Kovanen V, Vanharanta H, et al. Collagens in the injured porcine intervertebral disc. J Orthop Res 1994;12:93-102.  Back to cited text no. 11
    
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Ethier DB, Cain JE, Yaszemski MJ, Glover JM, Klucznik RP, Pyka RE, et al. The influence of anulotomy selection on disc competence. A radiographic, biomechanical, and histologic analysis. Spine (Phila Pa 1976) 1994;19:2071-6.  Back to cited text no. 12
    
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Nishida K, Kang JD, Suh JK, Robbins PD, Evans CH, Gilbertson LG, et al. Adenovirus-mediated gene transfer to nucleus pulposus cells. Implications for the treatment of intervertebral disc degeneration. Spine (Phila Pa 1976) 1998;23:2437-42.  Back to cited text no. 13
    
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Rousseau MA, Bass EC, Lotz JC. Ventral approach to the lumbar spine of the Sprague-Dawley rat. Lab Anim (NY) 2004;33:43-5.  Back to cited text no. 14
    
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Gebhard H, Bowles R, Dyke J, Saleh T, Doty S, Bonassar L, et al. Total disc replacement using a tissue-engineered intervertebral disc in vivo: New animal model and initial results. Evid Based Spine Care J 2010;1:62-6.  Back to cited text no. 15
    


    Figures

  [Figure 1], [Figure 2], [Figure 3]



 

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