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Low back pain is a common ailment affecting individuals around the globe. As per a recent study, majority of hours lost during work is due to low back pain. 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.
Researchers have used animal models to study the mechanism of lumbar disc diseases in various in-vivo studies like rabbit, sheep, goat, pig, dog etc. There even have been uses of in-vivo models of disc diseases for studying tissue engineering techniques like gene transfer, local hormonal injection and autologous cell implantation. 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.
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 intra-peritoneal organs, reduced pain in post-operative period, reduced surgical time and kept the surgeon away from the vessels like 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.
We used 7 male Sprague-Dawly rats, 3 months of age and weighing an average of 280 gm. The surgeries were conducted after ethical board approval and as per the current ethical norms.
A single intra-peritoneal 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.
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. The abdominal contents were allowed to hang and the surgeon faced the anterior abdominal area. The limbs were taped to the table. Surgery took place under strict aseptic precautions.
A curvi-linear incision was made in the lateral abdominal wall. The incision was made on the left side of the rat abdomen. Skin and sub-cutaneous tissue were meticulously dissected. External oblique was dissected in the direction of the fibers. The internal oblique muscle was found perpendicular to external oblique in the area just below it. It was dissected in the direction of the fibers. Transverse abdominus was encountered next and it was split vertically. Below the tranverse abdominus 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. The spine was visible from the lateral aspect without encountering any vessels/nerves or disturbing any vital organs. The muscles were approximated and the skin was closed with non-absorbable vertical mattress sutures.
After surgery, oral Meloxicam (5 mg/kg), was given and repeated every 12 hourly for 72 hours to control pain. Injection Ceftriaxone (30 mg per Kg) was given 12 hourly for three days to prevent post-operative infections. Food access remained unrestricted during the postoperative period.
Dorsal and ventral approaches have been described in the past to approach the animal spine however they suffer from a number of short comings. Dorsal approach is the simplest of the technique as it does not involve vital organs. However, it suffers with the limitations of exposing the rat discs or the anterior spinal structures completely. In order to reach the anterior structures with dorsal approach, the spine needs to be fractured or the rat needs to be sacrificed. Moreover, this technique leads to neurological damage in rat models due to the difficulty in approaching anterior structures via fractured spine. Ventral approach has been published in 2004 which discusses about targeting the anterior structures of rat spine. 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. 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 post-operative stage.
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