What is Ankylosing Spondylitis?

Ankylosing Spondylitis (AS) is one of the many forms of spondyloarthropathy or spondyloarthritis, and more specifically, a seronegative auto-immune spondyloarthropathy. AS is a chronic, progressive, inflammatory arthritis affecting the spine primarily, with involvement of other joints as well, especially the sacroiliac (SA) joint. It typically affects males (5:1) between 15 and 35 years of age, though children as young as 3 can show signs (Roberts and Manchester 158). The exact etiology is not clear though the gene HLA-B27 appears to have a primary role in AS and other seronegative spondyloarthropathies. 90-95% of AS patients test positive for HLA-B27, but not everyone with the gene develops AS (Roberts and Manchester 158). AS is seen more commonly in Caucasians and Native American populations and rarely in African Americans and Japanese.

Process of Fusion

-Inflammation of SA joints, unilateral or bilateral, followed by ankylosis

-Inflammation of intervertebral joints

-Healing of fibrous tissue produces calcification that ankyloses the synovial (apophyseal and costovertebral) joints of the spine

-Interspinous and superspinous ligaments also ossify, progressing from lumbar spine up

-Formation of bony syndesmophytes further fuse vertebrae

-Outer margins of fibrous intervertebral discs ossify

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The outcome of the spinal fusion is a smooth ‘bamboo spine’ appearance as the vertebral bodies lose their normal shape and become more square. Fusion of SA joints also occurs and can be either bilateral or unilateral.

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