How Bone Growth Causes Pain in Ankylosing Spondylitis

Medically Reviewed By William C. Lloyd III, MD, FACS
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For many types of arthritis, it’s the erosion of bone that drives pain. The opposite is true with ankylosing spondylitis (AS).  With AS, it’s the growth of new bone that causes pain and rigidity of the spine— two hallmarks of this inflammatory type of spinal arthritis.

In AS, the joints and ligaments along the spine become inflamed. As the disease progresses, the bones in the spine and pelvis area may fuse or grow together.

Exactly what causes new bone to grow in AS is not fully understood, but these spurs are visible in x-rays. As a direct result of the bone growth, the spine becomes stiff.  This makes any type of movement extremely uncomfortable. You can’t bend. You can’t turn, and eventually you just stop trying. In some extreme cases, AS can cause a hunched-forward posture.

In addition, there is an increased risk of spinal fracture due to decreased range of motion in the spine. The new bone is also inherently weak and brittle, which further increases the risk of fracture.

Treatments that halt the progression of AS may prevent bone growth and pain.

The first line of therapy is often nonsteroidal anti-inflammatory drugs (NSAIDs)—which are available in over-the-counter or prescription strengths. Taken when back pain flares, NSAIDs cool the inflammation that causes AS pain. They don’t necessarily prevent progression or bone growth, but not all people with AS will experience such a worsening of the disease.

Lifestyle changes count, too.

Regular exercise has a role in preserving flexibility in AS. Unlike other types of back pain, AS feels better with activity and worse with rest. Physical therapy, which stresses both strength training and flexibility, should also be an important part of AS treatment. It can help maintain range of motion in the back. Practicing good posture can help avoid stiffness and the downward curvature of the spine. Ask your doctor for tips on how you can practice good posture.

There is no specific AS diet, but staying trim can help relieve pressure on already inflamed joints. Eating foods that are rich in inflammation-fighting omega-3 fatty acids such as fatty fish pack a one-two punch against AS. Fish is a low-fat source of protein that can help you maintain a normal weight, and it has inflammation-fighting properties to boot.  

If NSAIDs are not enough to relieve the pain or side effects including gastrointestinal upset makes them hard to tolerate, other AS treatments are available. For example, steroids and disease-modifying drugs (sulfasalazine and methotrexate) work by reducing inflammation in the joints. They all have their share of benefits and drawbacks that must be discussed with your doctor.

Newer biologic drugs target tumor necrosis factor-alpha (TNF-a), a protein that is thought to kick start the inflammation cascade that leads to AS. There are currently five TNF-a blockers approved by the US Food and Drug Administration to treat AS. They include Enbrel (Etanercept), Remicade (Infliximab), Humira (Adalimumab), Simponi (Golimumab), and Cimzia (Certolizumab). Clinical research has shown that these TNF-a blockers can potentially slow or halt AS progression in some people. These drugs are given by intravenous infusion or injection. Potentially serious side effects may include increased risk of infection.

The decision to begin using these medications is not made lightly. It is based on your symptoms as well as how quickly your AS is advancing. This can be assessed via physical exams along with imaging and blood tests. In severe cases of AS, surgery may also be considered.

The best way to stay ahead of AS and painful bone growth is to keep in touch with your doctor. Schedule regular follow-up appointments and check-in when the pain or stiffness worsens.

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Medical Reviewer: William C. Lloyd III, MD, FACS
Last Review Date: 2021 Aug 15
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