Ankylosing spondylitis is chronic arthritis caused by inflammation of the spine that can result in significant back pain and problems with mobility.

“Ankylosing spondylitis primarily affects large joints in the body, particularly where there are a lot of ligament attachments to bone,” Themistocles Protopsaltis, MD, an associate professor of orthopedic surgery and neurosurgery who sees patients at NYU Langone’s Spine Center, tells HealthiNation.

Sometimes this condition leads to ankylosis, which is when the spine’s vertebrae fuse together, causing a person to lose mobility of the spine and become “stuck” in an abnormal position, such as with the head stooped forward. This may require surgery to straighten the spine, says Dr. Protopsaltis.

“As the disease progresses, and as people age, the bones can fuse together in a position that is not optimal,” says Dr. Protopsaltis.