Ankylosing spondylitis (AS) usually presents in the second or third decade. It affects mostly males but occasionally is reported in females.
Patients present with morning stiffness and persistent, sometimes progressive, axial pain. When the disease affects the major joints of the lower extremities (hips, knees), the patients will complain of pain in those regions as well.
Over time, enthesopathic changes appear and may, eventually, result in spine fusion. The fusion is caused by ossification of the anterior, posterior, and interspinous ligaments; the facet joints; and the discs. The spine ends up as a very rigid, solid structure known as bamboo spine (Figure 8-1). Lack of spinal motion interferes with the ability of the spine to withstand flexion and extension moments and brings about spinal osteoporosis. The spine becomes very fragile and as a result even simple, noncomplicated falls may lead to an unstable spinal fracture. In many instances the fracture occurs through the calcified discs (Figure 82). Because of this fragility, new-onset spinal pain should never be taken lightly in patients with AS. If X-rays of the painful region fail to detect an apparent fracture, bone scan and thin-slice CT or multislice CT with the multiplanar reconstructions may help reveal it at an early phase. Spine fractures are more common in the thoracic segments but may occur in the lumbar as well as the cervical regions.
In AS, the physical examination usually reveals decreased range of motion in the lumbar spine and the thoracic cage. The Schober test
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