Ankylosing Spondylitis
ankylosing spondylitis
Ankylosis (fusion)
- Ankylosing spondylitis is the major form of axial spondyloarthritis. Ankylosis means fusion.
Costovertebral joint fusion
- The most illustrative example of ankylosis (joint fusion) in ankylosing spondylitis is costovertebral joint fusion and other variants of chest wall ankylosis, which can result in reduced chest wall expansion and cause ventilatory impairment through chest wall restriction.
Sacroiliitis
- The key sites of fusion in ankylosing spondylitis are the sacroiliac joint, called sacroiliitis, and the lumbar spine.
- There is symmetric inflammation at the bilateral sacroiliac joints. This erosive process creates a "pseudo-widening" and ultimately an ankylosis of the joint. Sacroiliitis presents with SI joint tenderness.
Lumbar spine disease (Bamboo spine)
- For the lumbar spine, the vertebrae are squared (there edges are straightened) and there is reduction in height of the intervertebral spaces, which occurs via syndesmophyte bridges between the vertebrae (intervertebral bony bridges), creating a "bamboo" appearance.
- These lumbar changes manifest with profound pain and stiffness in the morning, which improves with exercises, and then worsens in the evening.
- Note that the Schober test is used to assess the degree of forward flexion of the lumbar spine.
Enthesitis
- Another important musculoskeletal manifestation is enthesitis (which we also address in psoriatic arthritis) – it's inflammation at the insertion of a tendon (such as the achilles), ligament, or joint capsule into the bone. The inflammation can lead to fibrosis (new bone formation).
HLA-B27 & Male sex
- Ankylosing spondylitis has a strong association with HLA-B27 and male sex. Roughly 90% of white individuals with the AS are HLA-B27 positive (it is less common in non-white patients).
Extraskeletal manifestations
- Uveitis, which can occur in up to one-third of patients.
- Aortic insufficiency and other cardiac manifestations.
- Additional spine complications, including discitis, cauda equina syndrome, and atlantoaxial subluxation.
- Pulmonary fibrosis along with the previously mentioned chest wall restriction.
- Kidney manifestations.