Multilevel laminectomy has been used to treat a variety of conditions of the cervical spine. In the adult population, it is most commonly used to treat cervical myelopathy resulting from spondylosis, ossification of the posterior longitudinal ligament (OPLL), or congenital stenosis. Less frequently, multilevel laminectomy is used to decompress the cervical spine in trauma or neoplastic conditions. In pediatric patients, the most common surgical indication is for tumor resection. Other indications for laminectomy in pediatric patients include Arnold-Chiari and syringomyelia decompression.

Multilevel laminectomy is an effective means to decompress the cervical spine. It provides a wide decompression and, when combined with foraminotomy, can decompress both the spinal cord and nerve roots. It is a relatively safe procedure and is generally well-tolerated by patients. Despite its efficacy in decompressing the neural elements, significant concerns have been raised about the destabilizing nature of this procedure with resultant changes in the sagittal alignment and alteration of normal biomechanics. The most concerning complication associated with this procedure is the development of postlaminectomy kyphosis. This sagittal plane imbalance places the spinal cord at risk and may result in new or cause an exacerbation of neurological symptoms. The objective of this chapter is to describe the incidence, biomechanics, prevention, and management of patients with postlaminectomy kyphosis.

The exact incidence of postlaminectomy instability remains unclear. The inability to provide the exact incidence is due to the multifactorial influence of age, preoperative diagnosis, preoperative sagittal alignment, and extent of bony resection on the occurrence of developing instability. Despite this fact, certain patients are definitely at higher risk for developing postoperative instability.

Children have the highest incidence of postlaminectomy kyphosis (1,2,3). The incidence of pediatric patients developing this complication ranges from 37% (1) to 95% in a series by Aronson et al. (4). The initial hypotheses that were suggested for the increased incidence of this complication in the pediatric population included the radiation of the postlaminectomized spine and aggressive facet resection. Yasuoka et al., after reviewing the radiographs of two patient groups (those patients over the age of 40 requiring surgery for postlaminectomy instability and patients under 25 who developed instability after multilevel laminectomy), suggested that there were two conditions that predisposed children to postlaminectomy deformity (5). The more common of the two findings was a wedging deformity of the anterior portion of the vertebral body. After laminectomy of the cervical spine, the biomechanics are altered, resulting in more load transmission through the anterior vertebral body (especially in flexion). In skeletally immature individuals with incomplete ossification of the vertebral bodies, this increased load can result in wedging of the anterior aspect of the body. This wedging deformity
will accentuate any sagittal plane imbalance. The second finding that was noted in children was excessive motion of the intervertebral spaces with flexion/extension moments. This was postulated to be due to increased viscoelastic properties of their intervertebral ligaments (i.e., interspinous and capsular ligaments). The significance of this becomes important when vertebral body wedging develops and the posterior ligaments are further stretched, resulting in more stress being placed on the anterior vertebral body. The inherent ligamentous laxity, combined with abnormal stresses, creates a cycle resulting in further wedging of the vertebral body and sagittal plane deformity.

Adults have a much lower incidence of postlaminectomy kyphosis, especially when there is normal preoperative sagittal alignment and no instability. Changes in overall sagittal alignment are more frequent, occurring in 21% to 47% of patients (6,7,8,9,10). Zdeblick and Bohlman proposed that this decreased incidence to develop postlaminectomy kyphosis in adults was due to stability imparted by the diffuse spondylosis seen in degenerative spines (11). Patients undergoing multilevel laminectomy for OPLL have also been thought to have a decreased incidence of postlaminectomy instability due to the ossification foci imparting stability. Mikawa et al. reviewed radiographs from adult patients who had undergone multilevel laminectomy for spondylosis, OPLL, and tumor, finding an 11% incidence of postoperative kyphotic or meandering types of deformity (10). Interestingly, OPLL accounted for 86% of these cases and spondylosis resection did not account for any (10).

Average cervical lordosis in asymptomatic patients ranges from 15 to 35 degrees (12,13). In this lordotic position, load transfer across the spine is preferentially distributed across the posterior elements. Pal and Sherk demonstrated that 36% of the axial compression passes through the anterior column while 64% is transmitted through the posterior column (32% per side) (14). The key structures that are responsible for load transmission—as well as maintaining stability—include the vertebral body, facet joints and associated capsule, interspinous ligaments, and the paraxial cervical spine musculature.

The facet joints and their associated capsular ligaments are the most critical elements in maintaining sagittal plane stability of the laminectomized spine. Facet resection may either occur as part of an aggressive laminectomy or as part of a foraminotomy to decompress nerve roots. Several studies have demonstrated that progressive facet resection results in cervical spine instability (15,16,17,18). Cusick et al. found that with unilateral facetectomy, the flexion-compression strength decreased by 32%, while bilateral facetectomy decreased strength by 53% (15). Zdeblick et al. demonstrated that foraminotomy involving removal of greater than 50% of the facet resulted in segmental hypermobility (17). In addition, Zdeblick et al. demonstrated that resection of greater than 50% of the facet capsule alone resulted in significant hypermobility during flexion/extension testing (19). The end biomechanical result of hypermobility in the sagittal plane due to excessive facet or capsular resection is more load transmission through the anterior column. This force, in the absence of the neutralizing posterior tension band, leads to a shifting of the weight-bearing axis resulting in sagittal plane imbalance. The end result of this process is postlaminectomy kyphosis.