Ankylosing spondylitis (AS) is a chronic inflammatory arthritis that primarily targets the spine. It affects the joints where ligaments and tendons attach to bone, leading to pain and stiffness. Kyphosis is a condition with an excessive forward curvature of the spine, often described as a “hunchback.” The connection is direct, as the inflammation from AS can cause spinal bones to fuse, locking the spine into a forward-bent position. This results in a rigid, structural kyphosis, which is different from postural kyphosis that is flexible and can be corrected by standing up straight.
The Pathophysiological Link Between AS and Kyphosis
Ankylosing spondylitis initiates inflammation in the spinal joints, particularly the sacroiliac joints where the spine connects to the pelvis. The body’s immune system mistakenly attacks the ligaments and their insertion points on the vertebrae, causing erosion and damage to bone and cartilage. This process is not limited to the spine and can also affect other joints like the hips and shoulders.
In response to this inflammation, the body starts a counterproductive healing process. It begins to deposit new bone material to repair the damage, a process called calcification and ossification, which occurs in the ligaments and discs between vertebrae. Over time, this new bone formation can bridge the gaps between vertebrae, causing them to fuse. This fusion, known as ankylosis, eliminates the spine’s natural flexibility.
The fusion process often solidifies the spine in a forward-bent posture. As more vertebrae fuse, this forward curve becomes more pronounced and permanent, creating a fixed thoracic kyphosis. The spine loses its normal alignment and becomes rigid in this stooped position. This structural change is irreversible without surgery and is a sign of advanced ankylosing spondylitis.
Symptoms and Diagnostic Process
The onset of ankylosing spondylitis is gradual, with symptoms that can fluctuate. Early signs include chronic lower back pain and stiffness, particularly around the pelvis, that worsens at night and is most severe in the morning. As the disease progresses, individuals may notice an increased forward curvature of their upper back, leading to a stooped posture. This can result in a measurable loss of height and difficulty standing straight.
Diagnosing kyphosis secondary to AS involves a physical examination and medical imaging. During a physical exam, a physician assesses the patient’s posture and measures the spine’s range of motion. They may also measure chest expansion, as rib joint involvement can limit the ability to take a deep breath. Blood tests can detect inflammatory markers and the HLA-B27 gene, which is found in many individuals with AS.
Imaging studies are used for a definitive diagnosis. X-rays can visualize the spine and reveal changes associated with AS, including the “bamboo spine” appearance in advanced stages where new bone bridges the vertebrae. Magnetic Resonance Imaging (MRI) can detect inflammation in the spine and sacroiliac joints before significant bone fusion has occurred. These techniques allow doctors to confirm the diagnosis and measure the severity of the kyphotic curve.
Non-Surgical and Surgical Interventions
Management of kyphosis in AS focuses on controlling the underlying disease and preserving spinal posture. Non-surgical treatments are the first line of defense and aim to reduce inflammation and maintain flexibility. Physical therapy involves specific stretching and extension exercises to counteract the forward pull on the spine and strengthen supporting muscles. Lifestyle modifications, like practicing good posture and sleeping on a firm surface, can also help prevent the spine from fusing in a bent position.
Medications are important for managing the inflammatory process of AS. Nonsteroidal anti-inflammatory drugs (NSAIDs) are used to alleviate pain and stiffness. For more aggressive disease, biologic medications, such as TNF or IL-17 inhibitors, can be prescribed. These drugs target specific parts of the immune system to control inflammation and can slow the progression of spinal fusion.
Surgical intervention is reserved for severe, debilitating cases of kyphosis. The primary surgical procedure is a spinal osteotomy. In this operation, a surgeon cuts through the fused vertebral column, realigns the spine into a more upright position, and uses instrumentation like rods and screws to hold it in place while it heals. This complex procedure can restore the ability to stand straight and look forward but is only considered when the deformity severely compromises quality of life.
Functional Impact on the Body
Severe kyphosis from ankylosing spondylitis can have significant effects on daily functioning. A primary challenge is the impairment of the horizontal gaze. When the head is fixed in a downward position, it becomes difficult to make eye contact, see obstacles while walking, or safely operate a vehicle. This can lead to social isolation and a loss of independence.
The stooped posture also impacts respiratory function. The forward curvature of the spine compresses the chest cavity, restricting the lungs’ ability to expand fully. This can lead to restrictive lung disease, causing shortness of breath, fatigue, and a reduced capacity for physical activity. The deformity can also create difficulties with swallowing and maintaining balance.