Ankylosing spondylitis (AS) is a chronic inflammatory disease that primarily targets the spinal joints, profoundly impacting their structure and function over time. It begins with inflammation in the sacroiliac joints, located where the spine meets the pelvis, and gradually progresses upward along the spine. This inflammation causes pain and stiffness, especially in the lower back and buttocks, which are often the earliest symptoms people notice.
The core way AS affects spinal joints is through persistent inflammation of the joints and the entheses—the sites where ligaments and tendons attach to bones. This inflammation triggers the body’s repair mechanisms, which unfortunately leads to the formation of new bone in these areas. Instead of restoring normal joint function, this new bone growth causes the vertebrae to gradually fuse together. This fusion process is called ankylosis.
Normally, the spinal joints allow for flexibility and movement, enabling bending, twisting, and turning. But as the vertebrae fuse, the spine loses its flexibility and becomes rigid. This loss of movement can be severe enough to create a characteristic “bamboo spine” appearance on X-rays, where the spine looks like a single, solid bone rather than a series of separate vertebrae. This fusion not only limits mobility but also changes posture, often causing a forward stoop or hunched back.
The impact on spinal joints is not limited to the vertebrae themselves. The inflammation can also affect the small joints between the vertebrae (facet joints) and the discs that cushion them. Over time, this can lead to chronic pain, stiffness, and reduced range of motion throughout the entire spine—from the lower back up through the mid and upper back, and even the neck.
In addition to bone fusion, the inflammation can cause swelling and damage to the cartilage and soft tissues around the joints. This contributes to joint pain and stiffness, especially after periods of rest or inactivity, such as in the morning. Movement and exercise often relieve this stiffness temporarily, but as the disease progresses, the pain and rigidity become more persistent.
The spinal changes caused by AS can also affect other functions. For example, when the ribs and spine fuse, chest expansion during breathing becomes limited, leading to breathing difficulties. The cervical spine (neck area) can also be involved, which may cause neck pain and stiffness and, in severe cases, neurological symptoms if nerves are compressed.
Because AS is a systemic disease, the inflammation and joint damage in the spine are often accompanied by symptoms in other parts of the body, such as inflammation in the eyes, heart, and other joints. But the hallmark of AS remains its progressive impact on the spinal joints, which can severely limit a person’s mobility and quality of life if not managed properly.
Managing AS involves controlling inflammation to slow down joint damage and maintain spinal mobility. Treatments include medications to reduce inflammation and pain, physical therapy to keep the spine flexible, and exercises tailored to avoid further joint stress. Early diagnosis and consistent management are crucial to prevent or delay the fusion process and preserve as much spinal function as possible.
In essence, ankylosing spondylitis transforms the spinal joints from flexible, mobile structures into rigid, fused segments through chronic inflammation and abnormal bone growth. This process leads to pain, stiffness, reduced movement, and postural changes that define the disease’s impact on the spine.