Adjacent Segment Disease (ASD) represents a condition that can emerge following spinal fusion surgery. Spinal fusion is a procedure designed to permanently join two or more vertebrae, aiming to stabilize a section of the spine and alleviate pain. However, this stabilization can lead to changes in the spinal segments directly above or below the fused area. This article explores the commonness of Adjacent Segment Disease and the various influences on its occurrence.
The Nature of Adjacent Segment Disease
Adjacent Segment Disease involves the accelerated degeneration of spinal segments next to a fused area. When vertebrae are fused, natural motion at that level is eliminated. This transfers increased stress and pressure to neighboring discs and joints, which compensate for the lost motion. This increased mechanical load accelerates wear and tear on these adjacent segments.
As a result, patients may experience symptoms similar to those that initially prompted the spinal fusion. Common manifestations include localized pain in the neck or back, which can sometimes radiate into the arms, hands, legs, or feet. Other symptoms may involve numbness, tingling, or muscle weakness in affected limbs. These issues arise as adjacent segments degenerate, potentially causing disc herniation, spinal stenosis, or facet joint arthritis.
How Often Does Adjacent Segment Disease Occur?
The reported rates of Adjacent Segment Disease can vary considerably, depending on how ASD is defined and the duration of follow-up after surgery. Researchers often distinguish between radiographic ASD, which refers to degenerative changes visible on imaging scans without necessarily causing symptoms, and symptomatic ASD, where these changes lead to noticeable pain and other issues. Radiographic ASD is more common, with reported occurrences ranging widely, from under 5% to over 90% in cervical spine studies. In lumbar spine studies, radiographic ASD has been reported with an incidence from 5% to 100%.
Symptomatic ASD, which involves actual discomfort requiring attention, occurs at lower rates. For the cervical spine, the pooled prevalence of symptomatic ASD is around 13.34%. The incidence of symptomatic ASD in the cervical spine can increase by approximately 2.9% per year, meaning about 25.6% of patients might experience it within 10 years after fusion. For the lumbar spine, the annual incidence of symptomatic ASD requiring further surgery has been reported at about 2.5% over the first 10 years. Cumulative rates for symptomatic ASD in the lumbar spine can range from 13.6% at 5 years to 22.2% at 10 years. The reoperation rate for ASD can be around 5.2% after lumbar fusion and 5.78% after cervical surgery.
Key Factors Contributing to ASD
Several elements contribute to the likelihood of developing Adjacent Segment Disease, encompassing patient-specific characteristics, surgical considerations, and biomechanical alterations. Patient-related factors include age, with older individuals having a higher risk. Pre-existing degeneration in adjacent spinal segments is a significant contributor, as these areas may be compromised before surgery. Conditions like obesity, smoking, and potentially genetics can also influence the risk.
Surgical factors play an important role. The number of spinal segments fused impacts the stress on neighboring levels; longer fusion constructs can impose greater mechanical stress. The specific level of fusion also matters, with certain areas like L4/L5 and L5/S1 (lumbar), and C5/C6 and C6/C7 (cervical), being more prone to ASD due to their inherent mobility. Surgical technique, including attention to spinal alignment and preserving soft tissues, can also influence outcomes.
Managing and Preventing Adjacent Segment Disease
Diagnosing Adjacent Segment Disease involves a thorough clinical evaluation, including patient history and physical examination, to assess symptoms and neurological deficits. Imaging studies such as X-rays, MRI, and CT scans are then used to identify degenerative changes in the segments next to the fusion and confirm the presence and extent of ASD.
Management of symptomatic ASD begins with conservative approaches, including physical therapy, pain medications such as NSAIDs, and injections to reduce inflammation and pain. If conservative treatments do not provide sufficient relief, surgical options may be considered, which might involve decompression or further fusion at the affected adjacent level. Strategies to prevent or delay ASD include careful patient selection, optimizing surgical techniques to minimize stress on adjacent segments, and maintaining proper spinal alignment during the initial fusion. Motion-preserving technologies, like artificial disc replacement, are also being explored as alternatives to fusion to reduce the risk of ASD.