Cervical fusion stabilizes the bones of the neck (cervical spine) to alleviate pain and neurological symptoms caused by instability or nerve compression. The surgery joins two or more vertebrae using a bone graft or artificial spacer, often secured with a plate and screws to encourage a solid bony connection. Although the procedure has a high success rate, sometimes the fusion fails to heal or maintain stability. Ongoing pain, stiffness, or a return of neurological symptoms after the expected recovery period indicate that the spine has not stabilized as intended. Understanding the cause of this failure is the necessary first step toward finding a solution.
Identifying the Reasons for Fusion Failure
The most common cause of a failed cervical fusion is pseudoarthrosis, where the bone graft fails to create a solid bony bridge between the vertebrae, resulting in a false joint. This lack of bony union stems from patient-specific and mechanical factors that interfere with the body’s natural healing process.
Lifestyle habits, such as smoking, are strong predictors of non-union because nicotine inhibits the function of osteoblasts, the cells responsible for forming new bone. Certain underlying health conditions can also impede fusion. These include diabetes, which affects blood flow and cellular healing, and osteoporosis, which involves low bone mineral density. Using chronic steroid medications or having poor nutritional status can similarly reduce the body’s capacity for robust healing.
Mechanical issues at the surgical site can also contribute to failure, even in otherwise healthy patients. This includes instrumentation failure, where the metal screws or plates break, loosen, or shift from their initial placement, leading to instability. Inadequate preparation of the fusion bed during the initial surgery, such as insufficient removal of the intervertebral disc or endplate cartilage, can also prevent the bone graft from integrating properly. Furthermore, fusing multiple segments of the spine increases the overall risk of non-union compared to a single-level procedure.
Diagnostic Confirmation of Non-Union
Confirming a non-union requires specific imaging studies that visualize the bony structure and assess for abnormal movement, as symptoms alone are insufficient for a definitive diagnosis. The initial step involves dynamic X-rays, which are images taken while the patient moves their neck into flexion and extension. These views allow physicians to measure movement between the fused segments; motion greater than one millimeter suggests instability and a lack of solid fusion.
To gain a detailed look at the bone graft itself, a high-resolution Computed Tomography (CT) scan is typically ordered. The CT scan is the most accurate imaging method for determining if a continuous bridge of bone, known as bridging bone, has formed across the fusion site. The presence of a radiolucent gap, or a clear space where bone should be, often confirms pseudoarthrosis.
A Magnetic Resonance Imaging (MRI) scan is sometimes used in the workup, though it is not the primary tool for assessing bone fusion. Instead, the MRI is valuable for evaluating soft tissue structures, such as checking for recurrent disc herniation, excessive scar tissue formation, or new compression on the spinal cord or nerve roots. Combining the information from dynamic X-rays and a CT scan provides the most complete picture of the mechanical and biological success of the original fusion.
Non-Surgical Management Before Revision
Before considering another operation, a structured non-surgical approach is attempted, especially if the non-union is stable or symptoms are mild. Targeted physical therapy focuses on strengthening the muscles surrounding the neck, providing external stability and support to the spine. This reduces mechanical strain on the unstable segment and alleviates pain without further invasive procedures.
Pain management strategies can also offer symptomatic relief while the body attempts to heal or while a patient prepares for a revision. These may include the use of non-steroidal anti-inflammatory medications or nerve-specific medications to manage persistent discomfort. Injections, such as epidural steroid injections, can be targeted to reduce localized nerve inflammation and swelling. In cases of a recent or minor non-union, a temporary external brace or collar may be prescribed to further immobilize the neck and promote bone healing.
Surgical Revision Approaches
When non-surgical treatments fail to provide lasting relief, or if instability is severe, surgical revision is necessary to correct the failed fusion. This procedure aims to achieve a solid fusion where the initial attempt failed, often requiring a more robust approach. A core part of the procedure involves extensive preparation of the fusion bed, including removing failed graft material, scar tissue, and the fibrous tissue that formed the pseudoarthrosis.
The surgeon will typically remove the original hardware, such as the plate and screws, and replace it with new, often stronger instrumentation to provide immediate stability. One significant decision involves the surgical approach. If the original surgery was performed from the front (anterior), the revision may be performed from the back (posterior), or vice versa. Posterior revision surgery is sometimes favored for non-union because it allows for a higher rate of successful bony fusion compared to a repeat anterior approach alone.
During the revision, a high-quality bone graft is used to maximize the chances of a successful union. This may involve using an autograft, which is bone harvested from the patient’s own body, as it contains living bone cells and growth factors that promote fusion. Biologic bone graft enhancers, such as bone morphogenetic protein (BMP), may also be utilized to stimulate bone growth at the surgical site. In some instances, the fusion may need to be extended to include additional adjacent segments if those segments have also become unstable or degenerative due to the stress placed on them after the original surgery.