Morphometrical analysis of the thoracolumbar dural sac in sheep using computed assisted myelography

Summary

Objectives

Sheep are frequently used as animal models in experimental spinal injury studies. Therefore, extensive knowledge of ovine spinal dimensions is essential for experimental design and interpretation of results obtained in these trials. This study aimed to obtain quantitative morphometrical data of the thoracolumbar dural sac in sheep and determine the anatomical relationship between the dural sac and the vertebral canal.

Methods

Computed assisted myelography imaging was carried out in five adult German Black-Headed Mutton sheep under general anaesthesia. Transverse images were acquired with 2 mm slice thickness from the first thoracic to the sixth lumbar vertebrae. Sagittal and transverse diameters and the cross-sectional area of the dural sac and vertebral canal were measured. To determine the anatomical relationship between the dural sac and vertebral canal, the pedicledural sac distance (PPSD) and the epidural space as well as the SAC (available space for the dural sac) were calculated.

Results

Sagittal diameters of the dural sac ranged from 5.1 to 12.0 mm. Transverse diameters ranged from 5.6 to 12.2 mm. The dural sac area covered 45.9% and 49.0% of the thoracic and lumbar vertebral canal area. The PDSD in the lumbar vertebrae was up to 15.8% larger than in the thoracic ones. The dural sac area was significantly positively correlated with the transverse diameter and area of the vertebral canal.

Clinical significance

The lumbar vertebral canal contained more space for the dural sac, which seems to be safer for testing spinal implants.

Keywords

Animal model - ovine - dural sac - myelography - computed tomography

• References

• 1 Wilke H, Wenger K, Claes L. Testing criteria for spinal implants: recommendations for the standardization of in vitro stability testing of spinal implants. Eur Spine J 1998; 7: 148-154.
• 2 Dickey P, Dumas A, Bednar A. Comparison of porcine and human lumbar spine flexion mechanics. Vet Comp Orthop Traumatol 2003; 16: 44-49.
• 3 Nout YS, Rosenzweig ES, Brock JH. et al. Animal models of neurologic disorders: a nonhuman primate model of spinal cord injury. Neurotherapeutics 2012; 9: 380-392.
• 4 Martini L, Fini M, Giavaresi G. et al. Sheep model in orthopedic research: a literature review. Comp Med 2001; 51: 292-299.
• 5 Rossignol S, Chau C, Giroux N. et al. The cat model of spinal injury. Prog Brain Res 2002; 137: 151-168.
• 6 Frigon A. The Cat Model of Spinal Cord Injury. In: Aldskogius H. editor. Animal Models of Spinal Cord Repair. New York: Humana Press; 2013. pg. 2013-159.
• 7 Soubeyrand M, Laemmel E, Dubory A. et al. Rat model of spinal cord injury preserving dura mater integrity and allowing measurements of cerebrospinal fluid pressure and spinal cord blood flow. Eur Spine J 2013; 1-10.
• 8 Konrad P, Tacker W, Levy W. et al. Motor evoked potentials in the dog: effects of global ischemia on spinal cord and peripheral nerve signals. Neurosurgery 1987; 20: 117-124.
• 9 Benneker M, Gisep A, Krebs L. et al. Development of an in vivo experimental model for percutaneous vertebroplasty in sheep. Vet Comp Orthop Traumatol 2012; 25: 173-177.
• 10 Turner AS. Experiences with sheep as an animal model for shoulder surgery: strengths and shortcomings. J Shoulder Elbow Surg 2007; 16: S158-S163.
• 11 Cain CC, Fraser RD. Bony and vascular anatomy of the normal cervical spine in the sheep. Spine 1995; 20: 759-764.
• 12 Vaccaro AR, Nachwalter RS, Klein GR. et al. The significance of thoracolumbar spinal canal size in spinal cord injury patients. Spine 2001; 26: 371-376.
• 13 Pavlov H, Torg J, Robie B. et al. Cervical spinal stenosis: determination with vertebral body ratio method. Radiology 1987; 164: 771-775.
• 14 Arlien-Søborg P, Kjaer L, Praestholm J. Myelography, CT, and MRI of the spinal canal in patients with myelopathy: a prospective study. Acta Neurol Scand 1993; 87: 95-102.
• 15 Azar-Kia B, Fine M, Naheedy MH. Importance of metrizamide CT for evaluation of the thoracic spine. Comput Radiol 1985; 9: 233-241.
• 16 Badami JP, Norman D, Barbaro NM. et al. Metrizamide CT myelography in cervical myelopathy and radiculopathy: correlation with conventional myelography and surgical findings. Am J Roentgenol 1985; 144: 675-680.
• 17 Nout Y, Reed S. Cervical vertebral stenotic myelopathy. Equine Vet Educ 2003; 15: 212-223.
• 18 Sharp NJ, Cofone M, Robertson ID. et al. Computed tomography in the evaluation of caudal cervical spondylomyelopathy of the Doberman Pinscher. Vet Radiol Ultrasound 1995; 36: 100-108.
• 19 da Costa RC, Echandi RL, Beauchamp D. Computed tomography myelographic findings in dogs with cervical spondylomyelopathy. Vet Radiol Ultrasound 2012; 53: 64-70.
• 20 Hara Y, Tagawa M, Ejima H. et al. Usefulness of computed tomography after myelography for surgery on dogs with cervical intervertebral disc protrusion. J Vet Med Sci 1994; 56: 791-794.
• 21 Hirabuki N, Mitomo M, Miura T. et al. Computed tomographic myelography characteristics of spinal cord atrophy in juvenile muscular atrophy of the upper extremity. Eur J Radiol 1991; 13: 215-219.
• 22 Naganawa T, Miyamoto K, Ogura H. et al. Comparison of magnetic resonance imaging and computed tomogram-myelography for evaluation of cross sections of cervical spinal morphology. Spine 2011; 36: 50-56.
• 23 Ogura H, Miyamoto K, Fukuta S. et al. Comparison of magnetic resonance imaging and computed tomography-myelography for quantitative evaluation of lumbar intracanalar cross-section. Yonsei Med J 2011; 52: 137-144.
• 24 Bolender N, Schönström N, Spengler D. Role of computed tomography and myelography in the diagnosis of central spinal stenosis. J Bone Joint Surg Am 1985; 67: 240-246.
• 25 Inoue H, Ohmori K, Takatsu T. et al. Morphological analysis of the cervical spinal canal, dural tube and spinal cord in normal individuals using CT myelography. Neuroradiology 1996; 38: 148-151.
• 26 Jones J, Wright J, Bartels J. Computed tomographic morphometry of the lumbosacral spine of dogs. Am J Vet Res 1995; 56: 1125-1132.
• 27 Yu Y, Du Boulay G, Stevens J. et al. Computed tomography in cervical spondylotic myelopathy and radiculopathy: visualisation of structures, myelographic comparison, cord measurements and clinical utility. Neuroradiology 1986; 28: 221-236.
• 28 Sherman J, Nassaux P, Citrin C. Measurements of the normal cervical spinal cord on MR imaging. Am J Neuroradiol 1990; 11: 369-372.
• 29 Tierney RT, Maldjian C, Mattacola CG. et al. Cervical spine stenosis measures in normal subjects. J Athl Train 2002; 37: 190-193.
• 30 Roberts R, Selcer B. Myelography and epidurography. Vet Clin North Am Small Anim Pract 1993; 23: 307-329.
• 31 Way TW, Chan H-P, Goodsitt MM. et al. Effect of CT scanning parameters on volumetric measurements of pulmonary nodules by 3D active contour segmentation: a phantom study. Phys Med Biol 2008; 53: 1295-1312.
• 32 Tins B. Technical aspects of CT imaging of the spine. Insights Imaging 2010; 1: 349-359.
• 33 Schönström N. The significance of oblique cuts on CT scans of the spinal canal in terms of anatomic measurements. Spine 1988; 13: 435-436.
• 34 Schwarz T, Saunders J. CT acquisition principle. In: Schwarz T, Saunders J. editors. Veterinary computed tomography. Oxford: Wiley-Blackwell 2011; 9-27.
• 35 Seiler G, Kinns J, Dennison S. et al. Vertebral column and spinal cord. In: Schwarz T, Saunders J. editors. Veterinary Computed Tomography. Oxford: Wiley-Blackwell; 2011. pg. 2011-209.
• 36 Beers GJ, Carter A, Leiter B. et al. Interobserver discrepancies in distance measurements from lumbar spine CT scans. Am J Roentgenol 1985; 144: 395-398.
• 37 Passantino A. Application of the 3Rs principles for animals used for experiments at the beginning of the 21st century. Annu Rev Biomed Sci 2008; 10: T27-T32.