Cervical Fusion Related Problems: Malalignment and Nonunions

Two common complications that occur in cervical surgery are malalignment, particularly after multilevel laminectomies, and nonunions. In both clinical situations, prevention and early recognition are critical in its respective clinical management. In postlaminectomy kyphosis, the prevailing cause is an alteration in the normal spinal biomechanics. The exact incidence is unknown; however, when this malalignment occurs, significant morbidity may be inflicted on the patient. Surgical treatment is the mainstay once a patient becomes symptomatic. Anterior cervical procedures are heavily utilized in the correction of the deformity. Like postlaminetomy kyphosis, nonunions can also largely be prevented. The incidence of pseudarthrosis has ranged from 0-50%. With advances in instrumentation and attention to surgical detail, the incidence has decreased. Fortunately, not all nonunions are symptomatic and warrant treatment. If symptomatic nonunion does occur, surgical options exist; anterior, posterior, and combined cervical procedures are viable options depending on the pathology. As the rate of cervical procedures increase in today’s population, it is paramount for any spine surgeon to be aware of these complications. Fortunately, if these complications do occur, the surgeon is armed with various methods to treat these deformities. Postlaminectomy Kyphosis Normal cervical lordosis ranges from 15-35 degrees. This sagittal curve results in preferential load distribution to the posterior elements; however, the vertebral body, facet joints and surrounding capsule, interspinous ligaments, and paraxial cervical spine musculature all contribute to the stabilization of lordosis. In cases where these structures are weakened or disturbed, this critical balance may result in cervical kyphosis. The causes of cervical kyphosis are numerous, yet a common etiology is via iatrogenic means, particularly due to aggressive facet resections in multilevel laminectomies. Several studies have demonstrated that progressive facet resection results in cervical spine instability. For example, Zdeblick et al reported that foraminotomies involving removal of greater than 50% of the facet resulted in segmental hypermobility, while Cusick et al found a 32% decrease in flexion-compression strength with unilateral facetectomy. Removal of 50% of the facet capsule alone also results in significant mobility during flexion and extension. Furthermore, disruption of the posterior tension band and denervation of the posterior cervical musculature can result in progressively increasing anterior compression loads that result in deformity, offering an explanation for the incidence of postoperative kyphosis in laminoplasty patients. Other risk factors for post-surgical kyphosis include age, preoperative sagittal alignment, intra-operative positioning, anterior graft complications such as extrusion and collapse, and posterior fusion without instrumentation. Regardless of the iatrogenic insult, hypermobility of the spine transfers load to the anterior column often leading to kyphosis. It should be noted, however, that extensive multilevel laminectomies do not immediately destabilize the spine. This article will discuss the specific management for postlaminectomy kyphosis. The exact incidence of postlaminectomy kyphosis is unknown; however, the incidence has been estimated at 20%. Furthermore, literature suggests that the incidence is higher in the younger population, likely a result of incomplete bone formation, resultant wedging deformity, and excessive motion of intervertebral spaces with cervical motion. In addition, the pediatric population is exposed to radiation in conjunction with posterior cervical fusion. Radiation can result in bone death and impaired bone growth, ultimately leading to kyphosis. In contrast, the adult population typically suffers from diffuse spondylosis, in effect stabilizing the cervical spine and preventing kyphosis. Early recognition of clinical symptoms due to postlaminectomy kyphosis is paramount in treatment. The typical clinical presentation of kyphosis is back or neck pain. Albert and Vaccaro described a “honeymoon” period when patients after laminectomy have transient improvement of neurological symptoms or remain symptomatically unchanged. As sagittal deformity occurs, the head assumes a position over the torso, placing the paraspinal musculature at a disadvantage. Eventually, muscle fatigue, facet joint arthopathy, or radiculopathy due to foraminal compression ensue, and if the deformity continues to progress, neurological symptoms such as myelopathy may appear. If kyphosis is suspected, radiographic evaluation includes static (Fig 1a) and dynamic radiographs. The extension radiograph will demonstrate the degree of lordosis that can be obtained. If a fixed sagittal deformity is discovered, a computerized tomography (CT) scan may be necessary for better bony evaluation as well as vertebral artery anatomy, both of which are paramount for surgical planning if a corpectomy is needed. A magnetic resonance image (MRI) is critical as well as this study can determine the cause of neurological symptoms and evaluate for intrinsic abnormalities to the cord that may increase the risk of surgery, such as myelomalacia, syrinx formation, and spinal cord atrophy (Fig 1b-c). Once symptomatic kyphosis occurs, surgical goals are to correct the sagittal plane deformity, stabilize the spine, and decompress any neural compression. In patients with flexible deformities and no ventral compression of the cord, an isolated posterior spinal fusion may suffice. Intraoperatively, the patient should be placed in a neutral position in a headholder to facilitate exposure and placement of instrumentation. Prior to final tightening of the instrumentation, the head should be extended to achieve lordosis. It should be noted, however, that whenever the cervical spine is extended, iatrogenic foraminal stenosis can potentially occur and should be treated accordingly. In other clinical situations, an anterior procedure should be included in the treatment plan. Fixed deformities with ankylotic facets should be treated with a posterior release supplemented with anterior correction. In fixed deformities without ankyloses, an anterior corpectomy or multiple level discectomies and fusion can be utilized. Studies, however, have demonstrated that an anterior construct alone increases the graft extrusion rate, so a posterior fusion usually is included as well. Riew et al reported on eighteen patients with postlaminectomy kyphosis treated with multilevel corpectomies with anterior strut grafting. Nine of the eleven complications were graft-related, resulting in the alteration in treatment protocol to include a circumferential fusion. Moreover, Herman and Sonntag studied twenty patients with postlaminectomy kyphosis in whom the mean kyphosis was 38 degrees. Traction improved the angle by 8 degrees. Open reduction via only an anterior approach and corpectomy improved the mean to 28 degrees. Steinmetz et al achieved on average 20 degrees of correction with the use of only an anterior approach. Multilevel anterior cervical discectomies and fusion provide greater segmental correction in the sagittal plane than corpectomies, yet segmental posterior fixation will also be required for definitive treatment. The authors’ preference is if there is ventral spinal cord compression by the vertebral bodies, corpectomies are recommended (Fig 1d-e). If, however, the patient does not have myelopathic findings and cord compression, but rather suffers from disc pathology, discectomies are