Evaluation of the influence of kyphosis and scoliosis on intervertebral disc extrusion in French bulldogs

Inglez de Souza et al. BMC Veterinary Research (2018) 14:5 DOI 10.1186/s12917-017-1316-9 RESEARCH ARTICLE Open Access Evaluation of the influence of kyphosis and scoliosis on intervertebral disc extrusion in French bulldogs Maria Claudia C. M. Inglez de Souza1,2, Richard Ryan2, Gert ter Haar2, Rowena M. A. Packer2, Holger A. Volk2 and Steven De Decker2* Abstract Background: Although thoracic vertebral malformations with kyphosis and scoliosis are often considered incidental findings on diagnostic imaging studies of screw-tailed brachycephalic breeds, they have been suggested to interfere with spinal biomechanics and intervertebral disc degeneration. It is however unknown if an abnormal spinal curvature also predisposes dogs to develop clinically relevant intervertebral disc herniations. The aim of this study was to evaluate if the occurrence of thoracic vertebral malformations, kyphosis or scoliosis would be associated with a higher prevalence of cervical or thoracolumbar intervertebral disc extrusion in French bulldogs. Results: French bulldogs that underwent computed tomography for reasons unrelated to spinal disease (n = 101), and French bulldogs with thoracolumbar (n = 47) or cervical intervertebral disc extrusion (n = 30) that underwent magnetic resonance imaging were included. There was a significant association between the presence of kyphosis and the occurrence of intervertebral disc extrusion, particularly in the thoracolumbar region. Dogs with kyphosis were at nearly a two times increased odds of being affected by intervertebral disc extrusion than those without kyphosis [(OR = 1.98 (95% CI: 1.04–3.78)]. There was also an association between the presence of scoliosis and the anatomical distribution of intervertebral disc extrusions, with dogs with scoliosis more likely to have more caudal lumbar intervertebral disc extrusions. Presence of scoliosis was not associated with an increased odds of being affected by intervertebral disc extrusion. Conclusions: Although thoracic vertebral malformations with kyphosis only rarely cause spinal cord dysfunction in itself, French bulldogs with kyphosis appear to be at higher risk to develop thoracolumbar intervertebral disc extrusion. Keywords: Vertebral malformation, Hemivertebra, Intervertebral disc disease, Intervertebral disc herniation, Brachycephalic Background Thoracic congenital vertebral body malformations, including hemivertebra with kyphosis and scoliosis are frequently encountered in brachycephalic screw-tailed dogs, such as the French bulldog (FB) [1–10]. The pathophysiological mechanism resulting in development of clinical signs is considered multifactorial with vertebral misalignment, instability and vertebral stenosis considered important factors [1, 3, 11]. This condition is however most often identified as an incidental radiological finding and 78% up to 93% of neurologically * Correspondence: 2 Department of Clinical Science and Services, Royal Veterinary College, University of London, Hawkshead lane, AL9 7TA North Mymms, Hatfield, UK Full list of author information is available at the end of the article normal FBs will demonstrate evidence of congenital vertebral body malformations with or without spinal kyphosis on diagnostic imaging studies of the vertebral column [3, 12, 13]. Recent studies have suggested that the severity of eventually present spinal kyphosis should be considered a critical factor in the development of spinal cord dysfunction [3, 7, 9]. Although thoracic vertebral body malformations with kyphosis is only rarely considered the primary cause of clinical signs, it has been suggested these malformations can be associated with alterations in spinal biomechanics [1, 3, 6, 7]. Changes in biomechanical properties can be associated with secondary degenerative changes of the vertebral column [6, 14, 15]. Thoracic vertebral body malformations with kyphosis have been associated with © The Author(s). 2018 Open Access This article is distributed under the terms of the Creative Commons Attribution 4.0 International License (http://creativecommons.org/licenses/by/4.0/), which permits unrestricted use, distribution, and reproduction in any medium, provided you give appropriate credit to the original author(s) and the source, provide a link to the Creative Commons license, and indicate if changes were made. The Creative Commons Public Domain Dedication waiver (http://creativecommons.org/publicdomain/zero/1.0/) applies to the data made available in this article, unless otherwise stated. Inglez de Souza et al. BMC Veterinary Research (2018) 14:5 subsequent early degeneration of adjacent intervertebral discs and altered distribution of intervertebral disc extrusions (IVDEs), along the vertebral column in FB [5]. It is currently however unclear if the presence of congenital thoracic vertebral body malformations with kyphosis or scoliosis also increases the actual risk of suffering from cervical or thoracolumbar IVDE. The aim of this retrospective observational study was therefore to investigate the relationship between congenital thoracic vertebral body malformations, kyphosis, and scoliosis and the occurrence of cervical and thoracolumbar IVDE in FBs. It was hypothesized that FBs with kyphosis or scoliosis would have an increased risk to develop IVDE, would have a different anatomical distribution of IVDE along the vertebral column and would develop IVDE at a younger age when compared with those without spinal curvature abnormalities. Methods Case selection The digital medical database of the Small Animal Referral Hospital, Royal Veterinary College was retrospectively reviewed from November 2010 to September 2016 to identify (1) a group of FBs with thoracolumbar or cervical IVDE (Hansen type I intervertebral disc disease) diagnosed by magnetic resonance imaging (MRI) [16, 17] and (2) a control group of FBs that underwent computed tomography (CT) of the thoracic vertebral column for reasons unrelated to spinal disease. For all dogs, the imaging studies and complete medical records had to be available for review. To be included in the first group, dogs had to have clinical signs and imaging findings compatible with IVDE. Dogs were excluded if the medical records or imaging studies were unavailable, if imaging studies did not include the complete thoracic vertebral column, or if any other orthopaedic or spinal disorder was detected. To be included in the second group, dogs had to be free of obvious clinical signs related to spinal or orthopaedic disease. Information retrieved from the medical records included age, gender, neutering status, clinical signs, reason for undergoing MRI or CT, final diagnosis, and initiated treatment. Imaging For the group of FBs with intervertebral disc disease, thoracolumbar or cervical IVDE was diagnosed by highfield MRI under general anesthesia (1.5 T scanner; Intera; Philips Medical Systems) and included a minimum of T2weighted (repetition time (ms) (TR)/ech (...truncated)