Spinal fractures in patients with ankylosing spondylitis

Transcription

1 Spinal fractures in patients with ankylosing spondylitis Poster No.: C-0847 Congress: ECR 2016 Type: Educational Exhibit Authors: M. Marino, A. Leone, A. Semprini, L. Tonetti, V. Zecchi, C Colosimo ; Roma/IT, Rome/IT Keywords: Trauma, Motility, Arthritides, Imaging sequences, MR, Digital radiography, CT, Musculoskeletal system, Musculoskeletal spine DOI: /ecr2016/C-0847 Any information contained in this pdf file is automatically generated from digital material submitted to EPOS by third parties in the form of scientific presentations. References to any names, marks, products, or services of third parties or hypertext links to thirdparty sites or information are provided solely as a convenience to you and do not in any way constitute or imply ECR's endorsement, sponsorship or recommendation of the third party, information, product or service. ECR is not responsible for the content of these pages and does not make any representations regarding the content or accuracy of material in this file. As per copyright regulations, any unauthorised use of the material or parts thereof as well as commercial reproduction or multiple distribution by any traditional or electronically based reproduction/publication method ist strictly prohibited. You agree to defend, indemnify, and hold ECR harmless from and against any and all claims, damages, costs, and expenses, including attorneys' fees, arising from or related to your use of these pages. Please note: Links to movies, ppt slideshows and any other multimedia files are not available in the pdf version of presentations. Page 1 of 27

2 Learning objectives The primary purposes of this educational exhibit were: to outline the factors that increase the incidence of vertebral fractures in patients with ankylosing spondylitis (AS); to review the radiological features of these conditions. Background Ankylosing spondylitis (AS) is a chronic autoimmune spondyloarthopathy mainly affecting the axial skeleton [1]. The ankylosed spine is prone to fracture even after a minor trauma and patients with AS have a fourfold vertebral fracture risk during their lifetime compared to healthy individuals [2, 3]. A delay in diagnosis often occurs due to both patient and doctor related factors. Even in the presence of symptomatic clinical vertebral fractures, patients frequently fail to differentiate acute fracture-type pain from preexisting inflammatory pain, so the diagnosis is often overruled by attributing the pain to disease activity [4, 5] (Fig. 1 on page 4). Page 2 of 27

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4 Fig. 1: Persistent mechanical back pain during 3-4 weeks in a 57-year-old man with AS. Lateral radiograph of the thoracolumbar spine shows ossification of the anterior longitudinal ligament except for L1-2 level (arrow) where the bony bridging is incomplete. This sign raised the suspicion of a fracture (Fig. 3). References: Institute of Radiology, Catholic University, School of Medicine, Rome/IT Furthermore, the absence of major trauma in the patient's history, as well as difficulties in fracture identification on the basis of radiography alone may also lead to a doctor's delay [3, 6]. Delayed diagnosis can worsen prognosis, as vertebral fractures are often unstable and require proper treatment in order to avoid primary and secondary neurological injury. Inflammation and new bone formation represent the two central features of AS promoting the pathological remodeling of the spine. Inflammation is characterized by enthesitis that determines ectopic bone formation within the affected structures and progressively leads to ossification of the spinal ligaments, intervertebral disks, endplates and apophyseal structures [1]. As the disease progresses, chronic inflammation promotes the development of syndesmophytes and causes the "squaring" of the endplates of vertebral bodies, finally resulting in the characteristic hyperkyphotic "bamboo spine" [1, 7]. AS is also associated with osteoporosis that is attributed to an uncoupling of the bone formation and bone resorption processes and promotes weakening of the spine as well as increased risk of vertebral fractures [5, 8, 9]. Biomechanically, the loss of flexibility of the fused spine results in a structure that behaves like a long bone and acts as a rigid lever, incapable of appropriately dissipating the energy of a traumatic event [1, 6, 10]. Susceptibility to spinal fractures in patients with AS is further increased by a significantly impaired mobility, as well as problems with balance and coordination that reduce the ability to take protective measures during a fall [1, 11]. Images for this section: Page 4 of 27

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6 Fig. 1: Persistent mechanical back pain during 3-4 weeks in a 57-year-old man with AS. Lateral radiograph of the thoracolumbar spine shows ossification of the anterior longitudinal ligament except for L1-2 level (arrow) where the bony bridging is incomplete. This sign raised the suspicion of a fracture (Fig. 3). Institute of Radiology, Catholic University, School of Medicine, Rome/IT Page 6 of 27

7 Findings and procedure details Mechanism of injury, location and types of fractures in AS patients Interestingly, fractures in AS patients have the following distinctive characteristics: the majority of fractures occur after low-energy trauma [1, 2, 6, 12-14]: due to its changed biomechanical properties, the forces needed to fracture an ankylosed spine are smaller than those required to fracture a normal spine. Therefore, in the AS spine even a trivial trauma (i.e. falls from standing/ sitting position) can result in a fracture of the vertebral body or its other components. Sometimes, fractures can occur without any recognizable trauma; hyperextension is the most frequently observed mechanism of injury [2, 12]; the lower cervical spine is the most commonly injured area because of its increased mobility, small vertebral bodies, oblique articular facets and the mobility of the skull on it [2-4, 15]; AS-related fractures usually pass through the vertebral body (transvertebral fractures) (Fig. 2 on page 16) or through the intervertebral disk (transdiskal fractures) (Fig. 3 on page 16) because of extensive osteopenic changes and loss of elasticity of the disks [2, 4, 12, 13, 15, 16]; both the anterior and posterior elements of the vertebra are often involved (Fig. 3 on page 16): as ossified ligaments and surrounding tissues are also damaged (Fig. 3 on page 16c), fractures of the ankylosed spine tend to be highly unstable and may be associated with neurological complications [1, 2, 4-6, 10-16]. Fig. 2: Lumbar transverse fracture in a 65-year-old woman after a fall from sitting position. a) Lateral radiograph of the thoracolumbar spine shows the fracture through Page 7 of 27

8 L1 vertebral body (arrow). b) Axial CT scan confirms the fracture extending to the middle column (arrows). References: Institute of Radiology, Catholic University, School of Medicine, Rome/IT Fig. 3: The same patient as in Fig. 1. a, b) Axial CT scans passing through L2 vertebra reveal bilateral non-displaced fracture at L2 pedicle-articular pillar junction (arrows in a and b). c, d) Sagittal multiplanar reformatted CT images clearly define the transverse intradiskal fracture involving the anterior and posterior longitudinal ligaments (arrows in c) and extending to posterior elements (arrow in d). References: Institute of Radiology, Catholic University, School of Medicine, Rome/IT Imaging modalities and findings Imaging of the spine plays a crucial role in the management of AS patients allowing an early detection of vertebral fractures and reducing the high rate of mortality and morbidity in such patients. Radiography Even when a fracture is clinically suspected, diagnosis can be difficult on the basis of radiography alone, given the highly abnormal spinal structure in patients with AS (ossified ligaments, surrounding osseous proliferation, poor outlining of the disk space, osteoporosis) [1, 3, 5, 6, 10, 13, 17]. Furthermore, the possibility to detect fractures Page 8 of 27

9 located in the lower cervical spine or fractures of the thoracic neural arch and its pedicles is reduced due to projection of the shoulder girdle [1, 3, 4, 6, 10] (Fig. 4 on page 17). The use of CT and MR imaging has been shown to increase the sensitivity of initial radiographic assessment [2, 6, 10, 12, 13]. Accordingly, CT should be used to image the spine whenever a patient with AS presents with new onset neck or back pain, no matter how minor or trivial the reported trauma, as it can demonstrate vertebral fractures in detail [1, 6, 12] (Fig. 4 on page 17a). Sometimes the suspicion of a fracture on radiography raises when the bony bridging due to the ossification of the anterior and posterior longitudinal ligament is incomplete (Fig. 1 on page 17). Fig. 4: 49-year-old-man with AS after a fall from a scaffold. a) Sagittal multiplanar reformatted CT image shows transverse fracture through the C7 vertebral body involving the ossified anterior and posterior longitudinal ligaments (arrow). b) Lateral radiograph does not show the lesion. References: Institute of Radiology, Catholic University, School of Medicine, Rome/IT CT CT of the spine is considered the reference standard for showing bony details, including fractures and fragments in patients with spinal fractures and AS. The new generation CT scanners with multiplanar reconstructions and three-dimensional (3D) volume rendered images can provide information regarding the extent of the lesion and help in visualization of the details of these fractures [12] (Fig. 2 on page 16, Fig. 3 on page 16, Fig. 4 on page 17a, Fig. 5 on page 19, Fig. 6 on page 19, and Fig. 7 on page 20). The most relevant sign of AS fractures is widening of the intervertebral space. Page 9 of 27

10 Fig. 5: The same patient as in Fig. 2. a) Sagittal reformatted, and b) 3D volumerendered CT images better define the through-and-through fracture involving the ossified anterior longitudinal ligament and the body of L1 to its posterior cortex (arrows in a, and b). Note the ankylosis of posterior spinal elements in b. References: Institute of Radiology, Catholic University, School of Medicine, Rome/IT Page 10 of 27

11 Fig. 6: Transverse fracture of C6 vertebra in a 70-year-old woman, after a fall from standing height, complicated by paralysis in both arms and paresis in both legs. a) Axial CT scan passing through C6 vertebra, b) midsagittal, and c) sagittal to the right of the midline multiplanar reformatted CT images show the highly displaced nature of the fracture involving all three columns of C6 vertebra. Note the severe vertebral osteoporosis, the laminar fragment encroaching the spinal cord (arrow in a, and b), the disruption of ossified anterior longitudinal ligament (double-head arrow in b), and the flaval ligament tear (arrow in c). References: Institute of Radiology, Catholic University, School of Medicine, Rome/IT Page 11 of 27

12 Fig. 7: High dens fracture associated with a Jefferson bursting fracture in a 63-yearold man with AS after a fall down. a) Axial CT scan shows the high dens fracture (white arrow) and the Jefferson bursting fracture with only a single fracture of the anterior arch (*), and bilateral fracture of the posterior arch (yellow arrows). b) Sagittal 3D volumerendered CT image shows the cranial displacement of the posterior arch fragment (arrows). c) Axial CT scan passing through the foramen magnum and d) sagittal multiplanar reformatted CT image demonstrate the displacement of the posterior arch fragment into the foramen magnum causing brainstem encroachment (yellow arrow in c, and d). The high dens fracture is well evident in d (white arrow). This injury was complicated by tetraplegia. References: Institute of Radiology, Catholic University, School of Medicine, Rome/IT Magnetic resonance (MR) Imaging Page 12 of 27

13 Many reports in the literature suggest the presence of neurological complications after vertebral fractures in patients with AS, including spinal cord and nerve root lesions, intramedullary edema, and paravertebral hematomas resulting in a variable degree of sensory and/or motor deficits [2, 6, 12, 18] (Fig. 6 on page 19, Fig. 7 on page 20, Fig. 8 on page 21, Fig. 9 on page 22, and Fig. 10 on page 23). Alaranta et al. [18] determined that the incidence of spinal cord injuries (SCI) in patients with AS was 11.4 times that in the population at large. The higher incidence of SCI in AS is, of course, correlated with the increased incidence of spinal fractures in these patients, but also directly related to the AS disease process. In fact, ossified spinal ligaments also fracture as part of the injury pattern, further decreasing the structural support available to the spine [1]. MR imaging is an excellent tool to evaluate soft tissues such as spinal ligaments, joint capsules and nervous structures, so it is considered the modality of choice to detect neurologic complications and a reasonable option to exclude occult fractures undetected by multi-detector CT [3, 13, 10, 17] (Fig. 8 on page 21, Fig. 9 on page 22b-c, and Fig. 10 on page 23). Bone and soft tissue near the fracture line become edematous for some time after trauma and increased signal intensity is readily detected on fluid sensitive fat-suppressed sequences, i.e. short-tau inversion recovery (STIR) or fat-saturated T2-weighted images (Fig. 8 on page 21c). The fracture line appears as a linear area of low signal intensity on both T1 and T2 sequences, unless fluid collection or hematoma are present inside the fracture line [12] (Fig. 10 on page 23). Fig. 8: The same patient as in Fig. 6. a) Sagittal T1-weighted, b) corresponding T2weighted, and c) fat-suppressed T2-weighted images confirm the acute fracture of C6 vertebra with extensive vertebral body edema and retropulsion, and define the position of the laminar fragment relative to the spinal cord (yellow arrow in b, and c). The resultant cord contusion that spans five vertebral levels is seen on the T2-weighted Page 13 of 27

14 images (small arrow in b, and c). Posterior longitudinal ligament stretching (white arrow in b, and c), and a heterogeneous prevertebral hematoma (* in a, b, and c) resulting from the anterior longitudinal ligament disruption are also evident. References: Institute of Radiology, Catholic University, School of Medicine, Rome/IT Fig. 9: The same patient as in Fig. 7. a) Sagittal multiplanar reformatted CT image shows, in addition to the already-mentioned fractures, chronic C5 and C6 fracture with ankylosis of the vertebral bodies forming a single vertebral block (arrow), and mild retropulsion of posterior wall fragment. Increase in the C4-5 interlaminar and interspinous distance reflects a posterior ligament complex tear (double-head arrow). b) Sagittal T2-weigthed MR image confirms the brainstem encroachment (yellow arrow) as well as the C5-6 vertebral body collapse (white arrow), with no evidence of signal changes in the cord. Due to the respiratory compromise, the patient had difficulty in remaining immobile during the examination. c) Sagittal T2-weighted MR image of the thoracolumbar spine showing chronic compression fracture of T12 vertebral body (*). Note the marrow signal is normal. The patient remained a complete tetraplegic until his death 9 days later for respiratory insufficiency. References: Institute of Radiology, Catholic University, School of Medicine, Rome/IT Page 14 of 27

15 Fig. 10: Transverse comminuted fracture of L5 vertebra with severe anterior displacement of the spine in a 56-year-old man after a simple fall. The patient was neurologically intact, with the sole complaint of lower back pain. a) Sagittal T1-weighted and b) corresponding fat-suppressed T2-weighted images show the fracture gap and the anterior subarachnoid space presenting with a low signal on T1-weighted image and a high signal on T2-weighted image (arrow in a, and b) (the signal of hematomas within the fracture gaps may vary with age). Note a heterogeneous dorsally located epidural collection extending from L1 to L5, which represents a spinal epidural hematoma (small arrows in b). References: Institute of Radiology, Catholic University, School of Medicine, Rome/IT Page 15 of 27

16 Images for this section: Fig. 2: Lumbar transverse fracture in a 65-year-old woman after a fall from sitting position. a) Lateral radiograph of the thoracolumbar spine shows the fracture through L1 vertebral body (arrow). b) Axial CT scan confirms the fracture extending to the middle column (arrows). Institute of Radiology, Catholic University, School of Medicine, Rome/IT Fig. 3: The same patient as in Fig. 1. a, b) Axial CT scans passing through L2 vertebra reveal bilateral non-displaced fracture at L2 pedicle-articular pillar junction (arrows in a and b). c, d) Sagittal multiplanar reformatted CT images clearly define the transverse Page 16 of 27

17 intradiskal fracture involving the anterior and posterior longitudinal ligaments (arrows in c) and extending to posterior elements (arrow in d). Institute of Radiology, Catholic University, School of Medicine, Rome/IT Fig. 4: 49-year-old-man with AS after a fall from a scaffold. a) Sagittal multiplanar reformatted CT image shows transverse fracture through the C7 vertebral body involving the ossified anterior and posterior longitudinal ligaments (arrow). b) Lateral radiograph does not show the lesion. Institute of Radiology, Catholic University, School of Medicine, Rome/IT Page 17 of 27

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19 Fig. 1: Persistent mechanical back pain during 3-4 weeks in a 57-year-old man with AS. Lateral radiograph of the thoracolumbar spine shows ossification of the anterior longitudinal ligament except for L1-2 level (arrow) where the bony bridging is incomplete. This sign raised the suspicion of a fracture (Fig. 3). Institute of Radiology, Catholic University, School of Medicine, Rome/IT Fig. 5: The same patient as in Fig. 2. a) Sagittal reformatted, and b) 3D volume-rendered CT images better define the through-and-through fracture involving the ossified anterior longitudinal ligament and the body of L1 to its posterior cortex (arrows in a, and b). Note the ankylosis of posterior spinal elements in b. Institute of Radiology, Catholic University, School of Medicine, Rome/IT Page 19 of 27

20 Fig. 6: Transverse fracture of C6 vertebra in a 70-year-old woman, after a fall from standing height, complicated by paralysis in both arms and paresis in both legs. a) Axial CT scan passing through C6 vertebra, b) midsagittal, and c) sagittal to the right of the midline multiplanar reformatted CT images show the highly displaced nature of the fracture involving all three columns of C6 vertebra. Note the severe vertebral osteoporosis, the laminar fragment encroaching the spinal cord (arrow in a, and b), the disruption of ossified anterior longitudinal ligament (double-head arrow in b), and the flaval ligament tear (arrow in c). Institute of Radiology, Catholic University, School of Medicine, Rome/IT Page 20 of 27

21 Fig. 7: High dens fracture associated with a Jefferson bursting fracture in a 63-year-old man with AS after a fall down. a) Axial CT scan shows the high dens fracture (white arrow) and the Jefferson bursting fracture with only a single fracture of the anterior arch (*), and bilateral fracture of the posterior arch (yellow arrows). b) Sagittal 3D volume-rendered CT image shows the cranial displacement of the posterior arch fragment (arrows). c) Axial CT scan passing through the foramen magnum and d) sagittal multiplanar reformatted CT image demonstrate the displacement of the posterior arch fragment into the foramen magnum causing brainstem encroachment (yellow arrow in c, and d). The high dens fracture is well evident in d (white arrow). This injury was complicated by tetraplegia. Institute of Radiology, Catholic University, School of Medicine, Rome/IT Page 21 of 27

22 Fig. 8: The same patient as in Fig. 6. a) Sagittal T1-weighted, b) corresponding T2weighted, and c) fat-suppressed T2-weighted images confirm the acute fracture of C6 vertebra with extensive vertebral body edema and retropulsion, and define the position of the laminar fragment relative to the spinal cord (yellow arrow in b, and c). The resultant cord contusion that spans five vertebral levels is seen on the T2-weighted images (small arrow in b, and c). Posterior longitudinal ligament stretching (white arrow in b, and c), and a heterogeneous prevertebral hematoma (* in a, b, and c) resulting from the anterior longitudinal ligament disruption are also evident. Institute of Radiology, Catholic University, School of Medicine, Rome/IT Fig. 9: The same patient as in Fig. 7. a) Sagittal multiplanar reformatted CT image shows, in addition to the already-mentioned fractures, chronic C5 and C6 fracture with ankylosis of the vertebral bodies forming a single vertebral block (arrow), and mild retropulsion Page 22 of 27

23 of posterior wall fragment. Increase in the C4-5 interlaminar and interspinous distance reflects a posterior ligament complex tear (double-head arrow). b) Sagittal T2-weigthed MR image confirms the brainstem encroachment (yellow arrow) as well as the C5-6 vertebral body collapse (white arrow), with no evidence of signal changes in the cord. Due to the respiratory compromise, the patient had difficulty in remaining immobile during the examination. c) Sagittal T2-weighted MR image of the thoracolumbar spine showing chronic compression fracture of T12 vertebral body (*). Note the marrow signal is normal. The patient remained a complete tetraplegic until his death 9 days later for respiratory insufficiency. Institute of Radiology, Catholic University, School of Medicine, Rome/IT Fig. 10: Transverse comminuted fracture of L5 vertebra with severe anterior displacement of the spine in a 56-year-old man after a simple fall. The patient was Page 23 of 27

24 neurologically intact, with the sole complaint of lower back pain. a) Sagittal T1-weighted and b) corresponding fat-suppressed T2-weighted images show the fracture gap and the anterior subarachnoid space presenting with a low signal on T1-weighted image and a high signal on T2-weighted image (arrow in a, and b) (the signal of hematomas within the fracture gaps may vary with age). Note a heterogeneous dorsally located epidural collection extending from L1 to L5, which represents a spinal epidural hematoma (small arrows in b). Institute of Radiology, Catholic University, School of Medicine, Rome/IT Page 24 of 27

25 Conclusion Spinal fractures are common in patients with AS and can occur even after minimal or no trauma. Fractures of the ankylosed spine tend to be unstable, because ossified ligaments also fracture. As a result, neurological complications represent a major risk. Recognition of these fractures can be challenging on the basis of radiographic examination alone. Patients with AS presenting with a trivial history of trauma or new pain symptoms should be critically evaluated for acute spinal fractures using CT and/or MR imaging, even if radiograph appears normal. Inadequate awareness and inappropriate management of these injuries can have devastating consequences. Therefore, it is important that doctors maintain a high level of suspicion for spinal injury in patients with known AS. Personal information M. Marino, Institute of Radiology, Catholic University, School of Medicine, Largo Agostino Gemelli 8, 00168, Rome. A. Leone, Institute of Radiology, Catholic University, School of Medicine, Largo Agostino Gemelli 8, 00168, Rome. A. Semprini, Institute of Radiology, Catholic University, School of Medicine, Largo Agostino Gemelli 8, 00168, Rome. L. Tonetti, Institute of Radiology, Catholic University, School of Medicine, Largo Agostino Gemelli 8, 00168, Rome. V. Zecchi, Institute of Radiology, Catholic University, School of Medicine, Largo Agostino Gemelli 8, 00168, Rome. C. Colosimo, Institute of Radiology, Catholic University, School of Medicine, Largo Agostino Gemelli 8, 00168, Rome. Page 25 of 27

26 References [1] Jacobs WB, Fehlings MG. Ankylosing spondylitis and spinal cord injury: origin, incidence, management, and avoidance. Neurosurg Focus 2008; 24(1): E12. [2] Westerveld LA, Verlaan JJ, Oner FC. Spinal fractures in patients with ankylosing spinal disorders: a systematic review of the literature on treatment, neurological status and complications. Eur Spine J 2009; 18(2): [3] Finkelstein JA, Chapman JR, Mirza S. Occult vertebral fractures in ankylosing spondylitis. Spinal Cord 1999; 37(6): [4] Sambrook PN, Geusens P. The epidemiology of osteoporosis and fractures in ankylosing spondylitis. Ther Adv Musculoskel Dis 2012; 4(4): [5] Geusens P, Vosse D, van der Linden S. Osteoporosis and vertebral fractures in ankylosing spondylitis. Curr Opin Rheumatol 2007; 19(4): [6] Waldman SK, Brown C, Lopez de Heredia L, Hughes RJ. Diagnosing and managing spinal injury in patients with ankylosing spondylitis. J Emerg Med 2013; 44(4): e315-e319. [7] Paparo F, Revelli M, Semprini A et al. Seronegative spondyloarthropathies: what radiologists should know. Radiol Med 2014; 119(3): [8] Davey-Ranasinghe N, Deodhar A. Osteoporosis and vertebral fractures in ankylosing spondylitis. Curr Opin Rheumatol 2013; 25(4): [9] Magrey M, Khan MA. Osteoporosis in ankylosing spondylitis. Curr Rheumatol Rep 2010; 12(5): [10] Thumbikat P, Hariharan RP, Ravichandran G, McClelland MR, Mathew KM. Spinal cord injury in patients with ankylosing spondylitis: a 10-year review. Spine 2007; 32(26): [11] Fatemi G, Gensler LS, Learch TJ, Weisman MH. Spine fractures in ankylosing spondylitis: a case report and review of imaging as well as predisposing factors to falls and fractures. Semin Arthritis Rheum 2014; 44(1): Page 26 of 27

27 [12] Wang YF, Teng MM, Chang CY, Wu HT, Wang ST. Imaging manifestations of spinal fractures in ankylosing spondylitis. AJNR Am J Neuroradiol 2005; 26(8): [13] Glace B, Dubost JJ, Ristori JM, Irthum B, Chazal J, Soubrier M. Transversal fractures in spinal ankylosis: a case series of 17 patients. Rev Med Interne 2011; 32(5): [14] Cooper C, Carbone L, Michet CJ, Atkinson EJ, O'Fallon WM, Melton LJ 3rd. Fracture risk in patients with ankylosing spondylitis: a population based study. J Rheumatol 1994; 21(10): [15] Kouyoumdjian P, Guerin P, Schaelderle C, Asencio G, Gille O. Fracture of the lower cervical spine in patients with ankylosing spondylitis: Retrospective study of 19 cases. Orthop Traumatol Surg Res 2012; 98(5): [16] Vosse D, Feldtkeller E, Erlendsson J, Geusens P, van der Linden S. Clinical vertebral fractures in patients with ankylosig spondylitis. J Rheumatol 2004; 31(10): [17] Cha TD, An HS. Cervical spine manifestations in patients with inflammatory arthritides. Nat Rev Rheumatol 2013; 9(7): [18] Alaranta H, Luoto S, Konttinen YT. Traumatic spinal cord injury as a complication to ankylosing spondylitis. An extended report. Clin Exp Rheumatol 2002; 20(1): Page 27 of 27