Ankylosing Spondylitis and Spine Surgery

Peer Reviewed

Ankylosing spondylitis (AS) is a type of chronic inflammatory arthritis that affects the spine’s bones, joints, and ligaments. AS is also known as von Bechterew’s disease, Marie-Strümpell disease, and rheumatoid spondylitis, and it is characterized by spinal stiffness and pain. It’s a progressive disease causing the spine’s bones and joints to fuse together, leading to rigidity and spinal deformity in advanced cases.

SpineUniverse talked with Neurosurgeon, Ali A. Baaj, MD, about ankylosing spondylitis, including its symptoms, diagnosis, and treatment. Dr. Baaj is Co-Director of the Spinal Deformity and Scoliosis Program at Weill Cornell Medicine’s Center for Comprehensive Spine Care in New York, NY. Ankylosing spondylitis is one of Dr. Baaj’s areas of specialization.
Healthy spine versus one with Ankylosing Spondylitis Ankylosing spondylitis is a type of chronic inflammatory arthritis causing the spine’s bones and joints to fuse together. Photo Source:

How common is ankylosing spondylitis, and who may be at risk?

Dr. Baaj: Ankylosing spondylitis is not a common disorder, roughly 1 to 1.5% of the population is affected. But its prevalence is more dependent on what part of the world you come from and your ancestry—some people are genetically predisposed to developing AS and may begin to experience symptoms during their teenage years. Ankylosing spondylitis affects men 3 times more often than women.

The hereditary aspect of ankylosing spondylitis was connected to the human leukocyte antigen HLA-B27 a long time ago. Presence of the antigen can be detected by a blood test. While HLA-B27 is strongly associated with AS, some people who have the antigen do not have nor will ever develop AS. Interestingly, this antigen is also associated with many other diseases, such as Crohn’s disease.

Please explain how AS can affect the spine.

Dr. Baaj: Ankylosing spondylitis most commonly affects the sacroiliac joints (SI joints) and may move up the spine into the thoracic (mid back) and cervical (neck) levels progressively over time. The chronic inflammatory nature of AS causes the vertebral segments to fuse together—this is sometimes called autofusion or autofusing. The disease can take over causing profound stiffening of the spine affecting the shape of the spinal column. The stiffening may lead to spinal rigidity increasing the risk for bone fracture.

Patients with severe AS may exhibit a flexed forward body position called kyphosis that can affect the lumbar, thoracic, and cervical regions (eg, thoracolumbar kyphosis). Sometimes this is also called fixed sagittal imbalance because the spinal column no longer is vertically straight or equal front/back, left/right sides.

The forward pitch of the thoracic and cervical spine can become so severe that a chin-on-chest deformity develops, making it difficult or impossible for the patient to move his or her head. In severe cases, the patient cannot see forward, and breathing and eating may become hampered.

How do these changes develop and progress?

Dr. Baaj: The spine’s vertebral bodies, such as those in the low back, may gradually develop a square-like shape. This change develops as connective tissues (eg, tendons, ligaments) thicken, grow, and attach to the disc’s annulus fibrosus; it’s almost like a sheath-like encasement of the vertebral bodies involved.

As ankylosing spondylitis progresses, the fibrous tissues, discs, and ligaments ossify, meaning they gradually turn into bone. The facet joints lose their cartilage and eventually fuse into solid unmovable masses. In some instances, the spine may appear like bamboo, and is sometimes called bamboo spine. In conjunction with these changes, spinal deformity gradually develops (eg, kyphosis).

What types of symptoms are related to AS?

Dr. Baaj: Pain and tenderness in the SI joints are usually the first symptoms reported. Stiffness may be localized (eg, low back) or felt throughout the spine when waking up; sometimes, these symptoms disrupt sleep. Low back pain may radiate into the buttocks and thighs.

The symptoms of AS are different from those caused by mechanical back pain, such as a sprain or strain. Exercise can improve mechanical back pain, whereas in ankylosing spondylitis, exercise usually increases symptoms.

Stiffness associated with ankylosing spondylitis affects spinal range of motion—that is, the ability to easily/smoothly move your back or neck forward, backward, and from side-to-side. When the thoracic spine is affected, pain and stiffness are felt in the mid back region, and chest expansion may be affected (eg, difficult to take a full deep breath).

When you evaluate a patient with AS, what’s involved?

Dr. Baaj: Of course, the patient’s medical and family histories are important, but I want to analyze how the disease is affecting the patient’s quality of life, and how we can improve that. Typically, that includes a physical and neurological examination and x-rays (eg, standing, lateral, flexion/extension). CT scans may be performed, too, especially during early manifestations of ankylosing spondylitis—as with any disease, early detection is important to long-term care.

Imaging tests are also used to measure spinal alignment and deformity. Also, depending on the patient’s symptoms, various physical tests may be performed to evaluate range of motion, flexibility, and balance. Many patients with AS may also be osteopenic, and DEXA scans would be recommended if major fusion surgery is considered.

At what point in a patient’s care do you become involved? Is it primarily for a surgical consultation?

Dr. Baaj: Often, I am part of the patient’s care team. The patient’s rheumatologist may prescribe a biologic or disease-modifying drug to manage the progressive nature of AS and/or anti-inflammatory medications. And while some patients with ankylosing spondylitis may never need spine surgery, their spinal disease often requires oversight or observation by a specialist like myself.

When AS only affects the sacroiliac (SI) joints, what treatment, if any, is recommended?

Dr. Baaj: It’s typical for AS to affect both SI joints. Treatment is usually non-surgical and can include anti-inflammatory drugs, sacroiliac joint injections, and physical therapy. Bracing is usually not effective to help relieve or manage ankylosing spondylitis-related SI joint pain.

When is spine surgery recommended to treat ankylosing spondylitis?

Dr. Baaj: Surgery is recommended to treat unstable fractures, progressive spinal deformity (eg, kyphosis, chin-on-chest deformity), and/or neurological deficits. Extremity weakness, loss of balance, problems walking, and abnormal reflexes are examples of neurologic dysfunction or deficit. It is imperative for a patient with known AS who suffers even minor trauma to be evaluated promptly. Fractures of the spine in a patient with AS are often highly unstable and can cause spinal cord injury if not treated promptly.

What is involved in a patient’s pre-operative evaluation?

Dr. Baaj: The evaluation, or pre-surgical planning, considers the levels or regions of the spine affected by ankylosing spondylitis, as well as the diagnosed problem. Assessing the potential benefits and risks of surgery must be carefully weighed and explained to the patient. Surgery for kyphotic spinal deformity with or without chin-on-chest is complex spine surgery often requiring removal of bone (ie, osteotomy).

Depending on the diagnosis, full-length x-rays are needed to evaluate the entire alignment of the spine, and used to measure where a deformity starts, ends, and its size. If the patient has a chin-on-chest deformity, the chin-brow angle is measured.

Furthermore, pre-operative images can be utilized to determine patient positioning on the operating table, incisions, osteotomies, and type and placement of spinal instrumentation. Pre-planning the entire surgical procedure is typical in these types of complex spine surgeries.

How may a fracture be treated?

Dr. Baaj: Considering the cervical spine (neck) and ankylosing spondylitis rigidity, fractures pose a heightened risk due to their close proximity to the spinal cord. Fracture may result from a simple injury or trauma. The risk is high for paralysis, bleeding, and death. Depending on the severity of the neck fracture, traction may be used to realign the spine and surgical stabilization (instrumentation and fusion) or halo vest immobilization until the fracture heals. Fractures in patients with AS are typically highly unstable “fracture dislocation” types. They require prompt surgical fixation with screws and rod systems. Kyphoplasty or vertebroplasty isn't typically effective at treating these fractures.

What surgical procedures are performed to treat spinal deformity caused by ankylosing spondylitis?

Dr. Baaj: Progressive and debilitating spinal deformity can occur in patients with AS. The goal of surgery is to realign and stabilize the spine in a manner that affords the patient the best posture possible. Whether in the cervical or thoracic spine (and sometimes lumbar spine), bony resection is needed (osteotomy) to “loosen” the spinal segments (eg, vertebral bodies) before spinal realignment and stabilization can take place. A stabilization system of screws and rods is used to hold the spine in the new alignment, and fusion material (ie, bone graft) is used to provide long-term stability.

Please explain a typical patient’s post-operative program of care.

Dr. Baaj: Regardless if a patient underwent surgery for fracture or deformity, the post-operative period can be challenging. After several days in the hospital, most patients will need inpatient rehabilitation for aggressive mobilization and physical therapy. Patients typically will need to be braced for at least 6-12 weeks after surgery. During that time, serial x-rays are performed every 3 to 6 months to assess the fusion. Potential complications include wound non-healing and delay fusion.

Updated on: 09/10/19
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Ali A. Baaj, MD
Associate Professor of Neurological Surgery
Cornell University
New York, NY
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