Adjacent segment disease is a condition that can develop following a spinal fusion surgery. This procedure involves permanently joining two or more vertebrae, which creates a solid, immobile block within the spine. Consequently, the spinal segments located directly above or below this fused area are subjected to increased stress and motion. This accelerated wear and tear can lead to degenerative changes in these adjacent segments, such as arthritis or spinal stenosis, a narrowing of the spinal canal.
Development of the Condition
Spinal fusion surgery achieves stability by eliminating movement at the treated levels. This rigidity, however, disrupts the natural distribution of forces along the spine. The spinal segments neighboring the fusion must compensate for the lack of motion in the fused segment, absorbing additional mechanical loads. This increased stress accelerates the natural aging process of the intervertebral discs and facet joints.
Think of the spine as a flexible chain; if several links are welded together, the links next to the weld will bend and twist more to accommodate movement, causing them to wear out faster. This accelerated degeneration can manifest as disc height loss, the formation of bone spurs, or instability. Pre-existing degeneration in the adjacent segments at the time of the initial surgery is a risk factor. Another contributing element is the number of spinal levels fused, as longer fusions create more stress on the neighboring segments.
Identifying the Symptoms
The most common indicator of adjacent segment disease is new or worsening back pain, often localized near the original spinal fusion. This pain may be distinct from the discomfort experienced before the initial surgery. Patients might also experience symptoms of nerve compression, which occurs when degenerative changes in the adjacent segments impinge on the spinal nerves.
One symptom is radiculopathy, which involves pain, numbness, or tingling that radiates from the spine into the arms or legs. The specific path of the pain depends on which nerve is affected. Another is neurogenic claudication, characterized by pain or weakness in the legs that intensifies with walking or standing and is typically relieved by sitting or bending forward. These symptoms arise as conditions like stenosis or a herniated disc develop in the overworked adjacent segments.
Diagnostic Process
Confirming a diagnosis of adjacent segment disease begins with a clinical evaluation. A physician will take a detailed patient history, focusing on the previous spinal fusion surgery and the new symptoms. This is followed by a physical examination to assess the patient’s range of motion, muscle strength, sensation, and reflexes. These steps help correlate symptoms with the specific spinal segments that may be affected.
Imaging studies are used to visualize the spine and confirm degenerative changes. X-rays, particularly flexion-extension views where the patient bends forward and backward, can reveal instability or arthritic changes in the vertebrae adjacent to the fusion. An MRI provides detailed images of soft tissues, allowing the doctor to see disc herniations, nerve compression, and the extent of spinal stenosis. A CT scan may also be used for a more detailed look at the bony structures.
Management and Treatment Approaches
The management of adjacent segment disease starts with conservative, non-surgical approaches. The goal of these treatments is to alleviate pain and improve function without additional surgery. These can include:
- Physical therapy to strengthen the core muscles that support the spine, which can help reduce the load on the affected segments.
- Anti-inflammatory medications to manage pain and reduce inflammation around the nerves.
- Activity modification, which involves avoiding movements and activities that exacerbate symptoms.
- Epidural steroid injections to deliver medication directly to the source of the inflammation.
When conservative treatments fail to provide adequate relief, or if neurological symptoms like weakness or numbness worsen, surgery may be considered. The surgical approach is tailored to the specific degenerative changes that have occurred. The objectives are to decompress the pinched nerves and stabilize the affected spinal segment. This often involves a laminectomy, a procedure to remove a portion of the vertebra to create more space for the nerves. In many cases, the surgeon may need to extend the original fusion to include the newly degenerated segment, which provides long-term stability.