A syndesmophyte is an abnormal, bony growth that develops within the ligaments of the spine, resulting in the fusion of adjacent vertebrae. This process of new bone formation, known as ossification, is a sign of an underlying inflammatory condition affecting the spinal joints. These growths develop slowly over time, bridging the spaces between vertebral bodies and leading to structural damage and reduced flexibility.
Understanding the Formation of Syndesmophytes
Syndesmophyte formation is a pathological process where soft connective tissue is replaced by bone. This ossification typically begins in the outer layer of the intervertebral disc, specifically the annulus fibrosus, and the longitudinal ligaments that run the length of the spine. The inflammatory process at the point where the ligament attaches to the bone, known as the enthesis, triggers the body to generate new bone as a form of misguided repair.
These bony structures are classified based on their appearance and origin. Marginal syndesmophytes are slender and tend to grow vertically and symmetrically from the edge of one vertebral body to the next. Non-marginal syndesmophytes, by contrast, are generally thicker, bulkier, and may grow horizontally or asymmetrically. When multiple marginal syndesmophytes fuse completely, they create a continuous column of bone, known as “bamboo spine” on X-ray, permanently eliminating the mobility of that spinal segment.
The Primary Conditions That Cause Syndesmophytes
The development of syndesmophytes is most strongly associated with a group of inflammatory joint diseases called spondyloarthropathies. Ankylosing Spondylitis (AS) is the most prominent of these conditions, where syndesmophytes are considered a hallmark of advanced disease. In AS, the marginal syndesmophytes usually appear thin and symmetrical, beginning predominantly in the lower spine and progressing upward. This pattern of growth directly correlates with the disease’s tendency to cause progressive spinal stiffness.
Other inflammatory arthropathies, such as Psoriatic Arthritis (PsA) and Reactive Arthritis, can also cause syndesmophytes to form. In these conditions, the growths are frequently non-marginal, appearing thick and asymmetrical, sometimes skipping vertebral levels. This difference in radiological appearance helps clinicians distinguish between the various types of spondyloarthropathies. It is also important to differentiate syndesmophytes from the bony bridges seen in Diffuse Idiopathic Skeletal Hyperostosis (DISH), a non-inflammatory condition that produces coarse, thick ossifications along the anterior longitudinal ligament.
Symptoms and Functional Consequences
The formation and progression of syndesmophytes result in a cascade of symptoms that directly impact a person’s quality of life and mobility. The most common experience is chronic back pain and increasing spinal stiffness, particularly noticeable in the morning or after periods of rest. As the bony bridges form and harden, the spine’s natural flexibility is progressively lost.
This loss of motion limits the range of movement in bending, twisting, and extending the back. In advanced cases, the continuous fusion of multiple vertebrae can lead to a fixed, forward-bent posture known as hyperkyphosis. This stooped position severely restricts a person’s ability to look straight ahead, creating functional challenges and making the rigid spine more susceptible to fracture from minor trauma.
Approaches to Treatment and Management
The primary goal of managing syndesmophytes is to control the underlying inflammatory disease to prevent new bone growth. Existing syndesmophytes cannot be reversed once fully ossified, so treatment focuses entirely on slowing or halting structural progression. Nonsteroidal anti-inflammatory drugs (NSAIDs) are a first-line treatment to reduce inflammation and pain, which helps slow the rate of disease progression.
For many patients, biologic therapies are utilized to target specific inflammatory pathways that drive new bone formation. Medications such as Tumor Necrosis Factor (TNF) inhibitors and Interleukin-17 (IL-17) inhibitors effectively suppress inflammation and may slow the development of new syndesmophytes. Physical therapy and regular exercise are fundamental components of management, aiming to maintain maximum spinal flexibility, strength, and good posture. In rare instances where severe spinal deformity significantly impairs vision or function, surgical intervention called an osteotomy may be performed to strategically cut and realign the fused spine.