Ankylosing Spondylitis

Ankylosing spondylitis (AS) is an inflammatory form of arthritis that mostly affects the spine and the sacroiliac joints. Over time it can cause vertebrae to fuse together, leading to stiffness and changes in posture. Early diagnosis and modern medications make a major difference in long-term outcomes.

What's happening in your spine

In AS, the body's immune system mistakenly attacks the joints and ligaments of the spine. Persistent inflammation triggers the body to lay down new bone where ligaments and joint capsules attach. Over years this new bone can bridge the spaces between vertebrae, gradually fusing the spine into a fixed position.

Common symptoms

• Slow-onset low back and buttock pain, usually before age 45
• Stiffness that is worst in the morning or after rest and improves with movement
• Pain that wakes you in the second half of the night
• Reduced flexibility — trouble bending forward, twisting, or looking up
• A stooped or rounded posture in later stages
• Fatigue; sometimes eye inflammation (uveitis) or hip and shoulder pain

Causes & risk factors

The exact cause is unknown but genetics play a large role — most patients carry the HLA-B27 gene marker. AS commonly begins in late teens to early thirties and is more often diagnosed in men, though women are affected as well.

How it's diagnosed

A rheumatologist usually leads the diagnosis. Workup includes a careful history, physical exam, blood tests (including HLA-B27 and inflammatory markers), X-rays of the SI joints, and MRI, which can show inflammation years before X-ray changes appear.

Treatment options

The goals of treatment are to control inflammation, preserve motion, and protect posture.

• Regular exercise and stretching — especially extension-based and postural exercises
• Physical therapy and aquatic therapy
• NSAIDs as a first-line medication
• Biologic medications (TNF inhibitors, IL-17 inhibitors) prescribed by a rheumatologist for active disease
• Smoking cessation, which slows disease progression

Surgery is reserved for patients who develop severe deformity, fractures of a fused spine, or significant nerve compression. Procedures include osteotomies to correct a forward-bent spine, fusion for unstable fractures, and decompression when nerves are pinched.

When to see a specialist

See a spine specialist if you have a known AS diagnosis with progressive deformity, a new injury to a fused spine, or new neurological symptoms such as numbness, weakness, or trouble walking. Even minor falls in patients with AS can cause serious spinal fractures and need urgent imaging.