Ovine Lumbar Intervertebral Disc Degeneration Model Utilizing a Lateral Retroperitoneal Drill Bit Injury
Summary
Intervertebral disc degeneration is a significant contributor to back pain and a leading cause of disability worldwide. Numerous animal models of intervertebral disc degeneration exist. We demonstrate an ovine model of intervertebral disc degeneration, utilizing a drill bit, which achieves a consistent disc injury and reproducible level of disc degeneration.
Abstract
Intervertebral disc degeneration is a significant contributor to the development of back pain and the leading cause of disability worldwide. Numerous animal models of intervertebral disc degeneration have been developed. The ideal animal model should closely mimic the human intervertebral disc with regard to morphology, biomechanical properties and the absence of notochordal cells. The sheep lumbar intervertebral disc model fulfils these criteria. We present an ovine model of intervertebral disc degeneration utilizing a drill bit injury through a lateral retroperitoneal approach. The lateral approach significantly reduces the incision and potential morbidity associated with the traditional anterior approach to the ovine spine. Utilization of a drill-bit method of injury affords the ability to produce a consistent and reproducible injury, of precise dimensions, that initiates a consistent degree of intervertebral disc degeneration. The focal nature of the annular and nucleus pulposus defect more closely mimics the clinical condition of focal intervertebral disc herniation. Sheep recover rapidly following this procedure and are typically mobile and eating within the hour. Intervertebral disc degeneration ensues and sheep undergo necropsy and subsequent analysis at periods from eight weeks. We believe that the drill bit injury model of intervertebral disc degeneration offers advantages over more conventional annular injury models.
Introduction
Lower back pain is the leading cause of disability worldwide1. Lumbar intervertebral disc degeneration associated discogenic pain is considered a significant contributor to lower back pain2. There is an increasing demand for reliable animal models of intervertebral disc disease for broadening the understanding of the degenerative process and for the investigation of potential therapies.
Numerous animal models of intervertebral disc degeneration exist3. Animals models used in the investigation of degenerative disc disease range in size from mice4, to larger mammals such as dogs5, sheep6, and non-human primates7. Methods used to induce intervertebral disc degeneration can be broadly classified into the categories of mechanical (e.g. intervertebral disc compression8 or surgical injury6), chemical (e.g. chemical nucleolysis5) or, less commonly, spontaneous degeneration (e.g. the sand rat9).
Given the complexity of human intervertebral disc degeneration, a perfect animal model does not exist. However, important considerations in choosing an appropriate animal model to mimic this condition closely have been identified3. Such considerations include the absence of notochordal cells (primitive cells with possible progenitor cell function10 absent from the adult nucleus pulposus in humans, sheep, goats and chondrodystrophic dogs but present in most mammals), similarities in animal and intervertebral disc size relative to humans, comparable biomechanical forces to the clinical condition, mechanistic and ethical considerations3.
Non-human primates meet many of the above criteria. Baboon and macaque models of spontaneous intervertebral disc degeneration have been described11,12,13. Both species spend large amounts of time in erect or semi-erect postures — a distinct advantage relative to other animal models. However, ethical and practical consideration (e.g. expense, housing, delayed onset of spontaneous degeneration) restrict their use in many institutions.
The ovine spine is an established model of intervertebral disc degeneration, with advantages including cellular, biomechanical and anatomical similarities to the human spine10,14,15. Despite the quadrupedal stature of sheep the ovine lumbar intervertebral disc is exposed to similar stresses to the human disc14. The ovine model is also more widely accepted, from an ethical perspective, than non-human primate models. Varied methods have been described to initiate the degenerative process, many of which require direct access to the intervertebral disc. Due to the termination of the spinal cord in the sacral region and ossification of the posterior longitudinal ligament in the ovine lumbar spine, posterior approaches to the intervertebral disc are technically challenging and less commonly used in the sheep16. The traditional access routes to the sheep lumbar spine, i.e. via anterior or anterolateral approaches, require large abdominal incisions, are fraught with risks of hernia, and damage to internal viscera and neurovascular structures16. The use of a relatively small lateral incision away from dependent abdominal areas may decrease such risks17.
We present an ovine model of degenerative lumbar intervertebral disc disease using drill bit injury performed through a minimally invasive lateral approach, and inspired by the work of Zhang et. al18. The goal of this protocol is to enable a reliable lumbar disc injury model that is readily reproducible, produces a consistent injury, and is safe and well tolerated. This approach is well-suited to investigators seeking to induce a milder degree of lumbar intervertebral disc degeneration than that observed with traditional surgical annulotomy (unpublished data) for the investigation of either intervertebral disc degeneration or regenerative therapies. These findings will be described in a forthcoming publication.
Protocol
Representative Results
Discussion
This minimally invasive lateral access approach is efficacious and safe with no post-operative herniae, abdominal wound dehiscence or infection observed in this series. Use of the drill bit intervertebral disc injury model with a depth stop provides a reproducible method of inducing a consistent intervertebral disc injury of known dimension (i.e. a 3.5 mm diameter x 12 mm depth injury in this study). In our experience, this method produces a less severe degree of disc degeneration than that observed in conventio…
Disclosures
The authors have nothing to disclose.
Acknowledgements
Dr. Chris Daly is the recipient of the Foundation for Surgery Richard Jepson Research Scholarship. The authors would like to thank Dr. Anne Gibbon, Dr. Dong Zhang and the staff of Monash Animal Services, Monash University for their assistance with animal surgery and care.
Materials
| Medetomidine Hydrochloride (10 mL Injection) | Therapon/Zoetis | PFIDOM10 | Multiple suppliers: Zoetis/Ilium |
| Thiopentone | Troy | Triothiopentone | Multiple suppliers: Neon Laboratories, Jagsonphal Pharmaceuticals |
| Isoflurane (2-3 % in oxygen) | Baxter | AHN3636 | Multiple suppliers: Baxter/VetOne |
| Amoxicillin parenteral | GlaxoSmithKline | JO1CA04 | Multiple suppliers: GlaxoSmithKline/Merck |
| Bupivacaine (0.5% Injection 20 mL) | Pfizer | 005BUP001 | Multiple suppliers: Pfizer/AstraZeneca |
| PVD Iodine Solution | Jurox | 61330 | Multiple suppliers: Jurox/Orion |
| Chlorhexidine 5%w/v | Jurox | Chlorhex C 5L (SCRUB) | Multiple suppliers: Jurox/Pfizer |
| Transdermal Fental Patch (75 μg/h) | Janssen-Cilag | S8-Dur7.5 | Multiple suppliers: Sandoz |
| Buprenorphine iv | Jurox | 504410 | Multiple suppliers: LGM Pharma |
| Atipamezole (Antisedan 0.06 mg/kg – 0.08 mg/kg) | Zoetis | PFIANT10 | Multiple suppliers: Ilium |
| Oster Golden A5 2-Speed Clippers | Oster | 078005-140-003 | Oster |
| 20 ml luer lock syringe | Terumo | 6SS+20L | Multiple suppliers: Medshop Australia/Terumo |
| 21 G IV needle | Terumo | SG3-1225 | Multiple suppliers:Medshop Australia/Terumo |
| #4 scalpel handle | Austvet | AD010/04 | Multiple suppliers: Austvet/SurgicalInstruments |
| #22 scalpel baldes | Austvet | ||
| Gillies tissue forceps | Austvet | AB430/15 | Multiple suppliers: Austvet/SurgicalInstruments |
| Metzenbaum curved dissecting scissors | Austvet | AC101/14 | Multiple suppliers: Austvet/SurgicalInstruments |
| Deaver retractor | Surgical Instruments | 23.75.03 | Multiple suppliers: Surgical Instrument/Austvet |
| Hohmann retractor | Austvet | KA173/35 | Multiple suppliers: Austvet/SurgicalInstruments |
| Mayo suture scissors | Austvet | AC911/14 | Multiple suppliers: Austvet/SurgicalInstruments |
| Needleholder 14 cm | EliteMedical | 18-1030 | Multiple suppliers: EliteMedical/Austvet |
| CMT 3.5 mm Brad-Point Drill | Carbatec | 516-035-51 | Multiple suppliers: Southeast Tool/Carbatec |
| Drill Bit Stop 4 mm | Drill Warehouse | 20121600 | Multiple suppliers: Amazon |
| Bosch 10.8 V Cordless Angle Drill | Get Tools Direct | GWB10.8V-LIBB | Multiple suppliers:Bunnings/Get Tools Direct |
| Autoclavable veterinary drill bag | AustVet | DRA043-AV | AustVet |
| 2-0 absorbable synthetic braided sutures | Ethicon | VCP335H | Ethicon |
| 3-0 absorbable synthetic braided sutures | Ethicon | VCP232H | Ethicon |
| Siemens 3 Tesla Skyra Widebore MRI | Siemens | N/A | Siemens |
| 9.4 Tesla Agilent (Varian) MRI | Agilent Technologies | N/A | Agilent Technologies |
| Atomscope HF 200 A Radiogaph | Radlink | 330003A | Multiple Suppliers: Radlink/DLC Australia |
| Veterinary Pulse Oximiter | DLC | 192500A | Multiple suppliers: DLC Australi Pty Ltd/AustVet |
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