Spinal fusion is a surgical procedure designed to connect two or more vertebrae in the spine, preventing independent movement between them. This process aims to enhance the spine’s structure and reduce pain or nerve-related symptoms by creating a single, solid bone segment. While generally effective in stabilizing the back, a spinal fusion can sometimes fail to achieve its intended goal, leading to what is often described as the fusion “breaking” or “not holding.” This article explores the various aspects of spinal fusion failure, including its underlying causes, recognizable signs, and available treatment approaches.
Understanding Spinal Fusion’s Stability
The primary goal of spinal fusion is to create a stable, immobile segment within the spine. Surgeons achieve this by using bone graft material, which acts as a scaffold to encourage new bone growth across the vertebrae. Bone graft can come from the patient’s own body (autograft), from a donor (allograft), or be a synthetic substitute. The bone graft stimulates the formation of new bone, gradually integrating with the existing vertebrae to form a solid union over several months to a year.
To provide immediate stability while this biological fusion process occurs, surgeons often implant instrumentation such as screws, rods, plates, or cages. These devices hold the vertebrae in proper alignment and restrict motion, creating an environment conducive to bone healing. It is the successful growth of new bone that provides long-term stability, not solely the implanted hardware. Spinal fusion procedures generally have a high success rate, typically ranging from 70% to 90%, depending on various individual and procedural factors.
Causes of Fusion Failure
Despite high success rates, spinal fusions can fail to achieve a solid union, a condition often referred to as pseudoarthrosis or non-union. In this scenario, the bone graft does not fully fuse the vertebrae, allowing continued motion at the surgical site. Several factors contribute to non-union, including lifestyle choices like smoking, which impairs bone healing by reducing blood flow and bone formation. Patient health conditions such as obesity, diabetes, and osteoporosis can also hinder the fusion process. Certain medications, including some nonsteroidal anti-inflammatory drugs (NSAIDs) and steroids, may interfere with bone healing.
Hardware failure, where implanted screws, rods, or plates break, loosen, or migrate, is another mechanism of fusion failure. This often occurs when the bone fusion itself does not take place or is incomplete, causing the hardware to bear excessive stress and eventually fatigue. While the hardware provides initial support, its long-term integrity depends on the successful biological fusion. Post-surgical infection, though less common, can also impede bone healing and contribute to fusion failure.
Adjacent segment disease (ASD) is another long-term complication. After spinal fusion, the segments above or below the fused area may experience increased stress and strain due to altered biomechanics. This increased load can lead to accelerated degeneration in these adjacent segments, causing issues like disc herniation, spinal stenosis, or facet joint arthritis. While ASD is a distinct condition from the fusion itself failing, it can result in new pain and neurological symptoms that require further attention.
Signs of a Failed Fusion
Persistent or worsening pain in the fused area is a common sign of failed spinal fusion. This pain may feel different from the pain experienced before surgery. It can be a dull ache or a sharp, burning sensation, sometimes radiating to the legs or arms if nerves are compressed. New onset of pain in areas adjacent to the fusion site can suggest the development of adjacent segment disease, where nearby spinal segments are experiencing increased stress.
Patients may also notice a loss of functional improvement, experiencing reduced mobility or difficulty with activities. Radicular symptoms, such as numbness, tingling, or weakness in the extremities, can signal nerve involvement. Audible clicking or grinding sensations might indicate issues with the implanted hardware. The appearance of a new spinal deformity could also be a physical sign of a fusion that has not adequately solidified.
Addressing a Failed Fusion
If a failed spinal fusion is suspected, a spine specialist conducts a thorough clinical evaluation. Diagnostic imaging plays a central role in confirming the issue. X-rays are commonly used to assess the position of hardware and observe bone growth. More detailed imaging, such as computed tomography (CT) scans, provides a clearer view of bone formation. Magnetic resonance imaging (MRI) is useful for evaluating soft tissues, nerves, and potential issues like disc herniation or nerve compression in adjacent segments.
Treatment options for a failed fusion vary. Non-surgical management, including pain management techniques, physical therapy, and bracing, may be considered for mild cases or when surgery is not an option. These conservative approaches aim to alleviate discomfort and improve function without further surgical intervention.
When non-surgical methods are insufficient or if imaging confirms non-union or hardware failure, revision surgery is often necessary. This procedure may involve removing or revising failed hardware, adding more bone graft, or extending the fusion to include additional spinal levels. The specific surgical approach is tailored to the individual’s condition, aiming to restore spinal stability and alleviate persistent symptoms.