The rate of symptomatic nonunion after anterior cervical discectomy and fusion varies from 5% to nearly 50%. Nonunion can be effectively treated through either an anterior, posterior, or combined approach. In addition to axial neck pain caused by nonunion, graft extrusion, or instrumentation failure leading to dysphagia or esophageal perforation, graft collapse causing kyphosis, and root or cord compression can occur. These additional factors need to be taken into consideration when planning surgical management.
Nonunion after anterior cervical discectomy and fusion (ACDF) has been noted since the initial description of the procedure in the late 1950s, and it has been shown to have a negative effect on outcome. Despite modification of the technique over the years, the rate of nonunion ranges up to 63% based on the fusion method (graft material, fixation, corpectomy vs. interbody grafting), the number of levels fused, and the smoking status of the patient.
Riley et al. were the first to describe the use of posterior cervical fusion using interspinous wiring for the treatment of nonunion after ACDF. They successfully achieved a fusion in the two patients treated with this method. Their results were confirmed by several other authors who reported bony fusion in 94% to 100% of patients treated with the technique. At the time that the posterior approach was first described for the treatment of anterior cervical nonunion, posterior wiring was one of the only fixation techniques available in the cervical spine. It provided a reliable method to obtain fusion using a primary instead of revision approach and provided a large, native bone surface area over which a fusion could occur. The posterior approach also allowed decompression of the nerve roots through a posterior foraminotomy. The technique could also be performed in conjunction with an anterior approach to provide semirigid fixation when an anterior approach to address graft extrusion or collapse, kyphosis, or cord compression was necessary. As newer types of fixation such as anterior plate and screw systems, and posterior screw and rod systems were developed, they have been shown to be useful in the treatment of cervical nonunions. The purpose of this chapter is to review the clinical symptoms, spectrum of disease and treatment options, indications and contraindications, and outcomes of patients with nonunions after anterior fusion of the cervical spine.
INDICATIONS AND CONTRAINDICATIONS
Surgery is indicated in patients with nonunions whose symptoms are unresponsive to nonoperative management and are limiting activities of daily living. However, many nonunions do not require surgery because they are either an asymptomatic radiographic finding only, are minimally symptomatic and do not limit activities, or respond to nonoperative treatment such as neck exercises, traction, and pain medication. In a series reported in 1972, DePalma et al. detailed 16 nonunions in a series of 150 patients undergoing ACDF. Only 1 patient (1/16) was reported as having unsuccessful results. White et al. reported that more than 50% of patients with pseudarthrosis in their series responded well. In a study of 23 patients with nonunion after ACDF, Newman found that 30% of his patients with nonunion had persistent symptoms that were not severe enough to require surgery; however, the remaining 70% did require surgery.
Most patients with symptomatic nonunions have axial neck pain. The pain is mechanical in nature, increasing with activities and relieved or improved with rest. The neck pain often begins 2 to 3 months after surgery and frequently occurs after the discontinuation of external cervical orthosis if these are used or when attempts are made to resume normal activities. Kuhns et al. found that the average time from the initial ACDF to the revision procedure in their series of 33 patients with pseudarthrosis was 16 months. Lowery et al. found that selective facet blocks routinely relieved axial neck pain when performed at the level of the nonunion and were a useful tool to confirm the pseudarthrosis level in most cases. Radicular symptoms may also occur in conjunction with axial neck pain and can be a useful clinical symptom that frequently correlates to the level of nonunion in the setting of multilevel fusions or can indicate the need to include a symptomatic adjacent segment as part of the salvage procedure. Nerve root blocks can be useful in instances where the diagnosis is not clear. Dysphagia caused by mechanical irritation or compression of the esophagus from graft or instrumentation migration or axial pain may also be a symptom associated with pseudarthrosis.
Plain radiographs alone are often adequate to identify a nonunion. Lateral flexion/extension radiographs demonstrating an interspinous measurement difference of greater than 2 mm have been found to a more reproducible and reliable method than the Cobb method for making the diagnosis of pseudarthrosis ( Fig. 32–1 ). Bone resorption or marginal sclerosis can often be seen in the intervertebral space. Implant breakage and loosening is also commonly found in the setting of pseudarthrosis, with a reported rate of 63% in one series. CT with sagittal reconstructions can also be useful in examining the graft bone interface for ingrowth ( Fig. 32–2 ). Esophageal and upper airway assessment for perforation and function with cine-esophagoscopy and direct laryngoscopy to evaluate for aspiration and vocal cord function may be necessary in instances where prominent implant or swallowing or speech dysfunction occurs ( Fig. 32–3 ). If an anterior approach using the opposite side of the neck than the original surgery is planned, vocal cord evaluation is mandatory.