Anteroposterior lumbar spine radiograph of a 42-year-old man with chronic back pain shows fused sacroiliac joints, vertebral body squaring, interspinous ligament calcification, flowing syndesmophytes, and posterior element fusion.
Lateral lumbar spine radiograph of the patient.
A 42-year-old man presents with complaints of chronic lower back pain. He has a history of T12 compression fracture as a result of a traumatic fall that occurred 5 years previously. He recovered well from the injury, but over the last few years, his entire back has become progressively more sore and stiff. Anteroposterior and lateral lumbar spine radiographs show fused sacroiliac joints, vertebral body squaring, interspinous ligament calcification, flowing syndesmophytes, and posterior element fusion.
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Radiographic findings that include fused sacroiliac joints, vertebral body squaring, interspinous ligament calcification, flowing syndesmophytes (bony growth that originates inside a ligament), and posterior element fusion are consistent with the diagnosis of ankylosing spondylitis (AS). AS is a seronegative spondyloarthropathy of unknown etiology that affects primarily the axial skeleton. Testing for human leukocyte antigen (HLA)-B27 is positive in 90% of those with AS.
Enthesitis or enthesopathy are the main clinical features of AS that help differentiate it from rheumatoid arthritis. Enthesopathy is inflammation at the tendon and ligament insertion that leads to bony destruction, surrounding soft tissue ossification, and new bone formation with eventual joint ankylosis. Ankylosis and loss of spine motion lead to syndesmophyte formation and the characteristic “bamboo spine” appearance on lateral radiograph.1,2
Systemic manifestations of AS may include uveitis, cardiac abnormalities, and susceptibility to Klebsiella pneumoniae synovitis. Musculoskeletal manifestations may include bilateral sacroiliitis, progressive kyphosis, cervical spine fracture, and hip and shoulder arthritis. Low bone density and osteoporosis are found in up to 62% of those with AS, explaining the higher incidence of compression fractures in these individuals.
AS is diagnosed using the modified New York criteria, which includes lower back pain for at least 3 months that improves with exercise and is not relieved with rest, limitation with lumbar spine motion, decreased chest expansion relative to normal values for same age and sex, and radiographic criteria of bilateral sacroiliitis grade 2 to 4 or unilateral sacroiliitis grade 3 to 4.1,2
Dagan Cloutier, MPAS, PA-C, practices in a multispecialty orthopedic group in the southern New Hampshire region and is editor-in-chief of the Journal of Orthopedics for Physician Assistants (JOPA).
- Kubiak EN, Moskovich R, Errico TJ, Di Cesare PE. Orthopedic management of ankylosing spondylitis. J Am Acad Orthop Surg. 2005;13:267-278.
- Moore D. Ankylosing Spondylitis. Orthobullets website. http://www.orthobullets.com/spine/2044/ankylosing-spondylitis. Accessed February 7, 2017.