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Predisposition for Spinal Fracture in Ankylosing Spondylitis

¹ Department of Radiology, Harborview Medical Center, University of Washington School of Medicine, 325 Ninth Ave., Seattle, WA 98104.
² Department of Orthopedics, Harborview Medical Center, University of Washington School of Medicine, Seattle, WA 98104.

 
This is another in the continuing series on radiology in trauma cases from the Harborview Medical Center. Editors: Fred A. Mann, Eric J. Stern, and Alexander B. Baxter.

Address correspondence to F. A. Mann

Introduction

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A 40-year-old man with established ankylosing spondylitis of the lower spine was struck by a car and sustained an isolated back injury with thoracolumbar junction tenderness and swelling. Mild bilateral hip flexion weakness was present with no other neurologic deficit. Lumbar spine radiographs showed an unstable extension fracture—dislocation through the L1-L2 disk space (Fig. 1A) and characteristic features of ankylosing spondylitis. He underwent posterior fusion and instrumentation from T12 to L3. Minimal iliopsoas weakness persisted.

View larger version (63K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1 .—40-year-old man with ankylosing spondylitis who was struck by car and sustained isolated back injury. Two years later he was readmitted with lower back pain after series of falls. A, Lateral lumbar spine radiograph shows extension fracture-dislocation through L1-L2 disk space (black arrow). Note ankylosis of posterior spinal elements (White arrow).

Two years later the patient was readmitted with lower back pain after a series of falls. The lateral lumbar spine radiograph (Fig. 1B) showed new widening of the L4-L5 disk space and a transverse fracture through the fused articular facets; these findings were confirmed on CT (Fig. 1C). He underwent extension of the posterior fusion and instrumentation to the L5 level without further neurologic deterioration.

View larger version (81K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1 .—40-year-old man with ankylosing spondylitis who was struck by car and sustained isolated back injury. Two years later he was readmitted with lower back pain after series of falls. B, Two years later, lateral lumbar spine radiograph shows new widening of L4-L5 disk space (thick arrow) with transverse fracture through ossified facet joints below prior fusion (thin arrow).

View larger version (112K): [in this window] [in a new window] [as a PowerPoint slide]   Fig. 1 .—40-year-old man with ankylosing spondylitis who was struck by car and sustained isolated back injury. Two years later he was readmitted with lower back pain after series of falls. C, Axial CT scan with 3-mm collimation and sagittal reformation confirms injury (arrow).

The diffuse paraspinal ossification and inflammatory osteitis of advanced ankylosing spondylitis creates a fused, brittle spine that is susceptible to fracture. Even minor trauma can produce an unstable injury as a result of disruption of the ossified supporting ligaments.

Thoracolumbar fractures are reported less frequently than cervical injuries in patients with ankylosing spondylitis [1, 2]. Three recognized patterns are simple vertebral compression fractures, transversely oriented shear fractures, and stress fractures associated with pseudoarthrosis [3].

Simple vertebral compression fractures are osteoporosis-related injuries that occur early in the course of the disease, before ankylosis, and typically result in stable kyphosis [3]. Transversely oriented shear fractures are acute fractures of the ankylosed spine that invariably disrupt the ossified supporting ligaments and usually traverse the disk space. Disruption of all three columns of the spine predisposes the fracture to displacement and neurologic injury [3]. Stress fractures associated with pseudoarthrosis are subacute injuries that constitute part of the spectrum of spondylodiscitis, a destructive discovertebral ("Andersson") lesion, that tends to occur in the thoracolumbar region [4, 5]. End-plate erosions and disk height changes, with vertebral sclerosis or osteolysis, can be seen radiographically. Although the inflammatory process may play a role, many cases are probably caused by the nonunion of stress fractures [4]. These fractures are more stable than transversely oriented shear fractures, with infrequent neurologic sequelae [3].

The recognition of minimally displaced fractures in patients with ankylosing spondylitis is compromised by coexisting osteopenia and deformity. One must specifically search for disk space widening and discontinuity of the ossified paraspinal ligaments. New back pain in patients with ankylosing spondylitis or other diseases with paraspinal ossification should be assumed to be caused by fracture until disproven. Axial CT has potential diagnostic limitations because of the transverse fracture plane; sagittal reformations should be obtained. In problem cases MR imaging and radionuclide scintigraphy [6] can be helpful.

Our patient sustained two unstable transdiskal lumbar spine injuries within a 2-year period, reflecting the predisposition for spine fracture in ankylosing spondylitis. Prompt reduction and stabilization of the first injury resulted in favorable neurologic outcome. The site of the second fracture, which followed only minor trauma, was influenced by altered biomechanics at the margin of the previous fusion.

References

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1. Thorngren KG, Liedberg E, Aspelin P. Fractures of the thoracic and lumbar spine in ankylosing spondylitis. Arch Orthop Trauma Surg 1981;98:101-107
2. Olerud C, Frost A, Bring J. Spinal fractures in patients with ankylosing spondylitis. Eur Spine J 1996;5:51-55[Medline]
3. Trent G, Armstrong GWD, O'Neil J. Thoracolumbar fractures in ankylosing spondylitis: high risk injuries. Clin Orthop 1988;227:61-66[Medline]
4. Gelman MI, Umber JS. Fractures of the thoracolumbar spine in ankylosing spondylitis. AJR 1978;130:485-491[Abstract]
5. Rasker JJ, Prevo RL, Lanting PJH. Spondylodiscitis in ankylosing spondylitis, infection or trauma? A description of six cases. Scand J Rheumatol 1996;25:52-57[Medline]
6. Resnick D, Williamson S, Alazraki S. Focal spinal abnormalities on bone scans in ankylosing spondylitis: a clue to the presence of fracture or pseudarthrosis. Clin Nucl Med 1981;6:213-217[Medline]

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This Article Figures Only Full Text (PDF) Alert me when this article is cited Alert me if a correction is posted Services Email this article to a friend Similar articles in this journal Similar articles in PubMed Alert me to new issues of the journal Download to citation manager Citing Articles Citing Articles via Google Scholar Google Scholar Articles by Hanson, J. A. Articles by Mirza, S. Search for Related Content PubMed PubMed Citation Articles by Hanson, J. A. Articles by Mirza, S. Social Bookmarking                      What's this?