Postlaminectomy kyphosis is a not too infrequent complication of posterior cervical spine surgery. In less severe cases, it can result in persistent mechanical neck pain. In more severe cases, it can be associated with debilitating pain, neurologic deficits, and significant functional impairment. The management of these deformities requires a thorough radiographic and clinical assessment to develop an appropriate surgical strategy. This chapter summarizes the management strategies for postlaminectomy kyphosis.
The indications for surgery are progression of the deformity, intractable neck or radicular pain, myelopathy, or functional impairment caused by a significantly flexed head and neck posture.
Surgical management may require an anterior, posterior, or a combined anterior and posterior approach.
The selection of the appropriate surgical approach requires a thorough clinical and radiographic assessment of the patient before surgery.
The goals of management include decompression of the neural elements and restoration of sagittal balance.
A trial of preoperative cranial traction may be helpful in partially reducing the kyphotic deformity.
The preoperative rigidity/flexibility of the deformity and the presence of any neural compression will guide the selection of the surgical approach.
A deformity in which the posterior facet joints are fused will require an initial posterior approach to perform multilevel osteotomies.
A deformity in which the facet joints are not fused may be able to be managed through an anterior approach.
Rigid deformities with evidence of neural compression may require a multistage, combined anteroposterior approach.
Decompression of the neural elements should be performed before correction of the deformity is attempted.
Failure to achieve both a wide anterior and posterior release of the cervical spine will limit the ability to achieve correction of a rigid deformity.
Failure to restore the cervical spine to at least a straightened posture will potentially lead to delayed progression of the deformity.
Insufficient construct design is a common cause of delayed deformity progression.
The cervical spine is composed of vertebrae that articulate with each other via facet joints oriented in the coronal plane. This, combined with the lack of external bracing provided by a rib cage, allows for greater range of motion than is found in the thoracic or lumbar spinal regions. However, it also creates a greater dependency on the supporting paraspinal muscles and ligaments for long-term stability. When these structures are sufficiently compromised by damage, disease, or removal, a deformity of the cervical spine in the sagittal plane may occur.
Kyphosis of the cervical spine has several causative factors. It may develop secondary to advanced degenerative disorders, trauma, or neoplastic disease. It has also been associated with systemic arteritides such as ankylosing spondylitis and rheumatoid arthritis. However, the most common cause of cervical kyphosis is iatrogenic (i.e., after surgery). This form of kyphosis may occur after either anterior or posterior cervical surgery. After anterior cervical surgery, kyphosis may develop as a result of failure to adequately secure anterior spinal column support. This typically occurs because of pseudoarthrosis with bone graft collapse or dislodgement ( Fig. 34-1 ).
After posterior surgery, kyphosis may develop because of the disruption of the stabilizing bony, ligamentous, and muscular structures of the posterior spinal column ( Fig. 34-2 ). The potential destabilizing effect of a cervical laminectomy is well recognized. The incidence of kyphosis in this setting has been estimated to be as high as 21%. It may vary according to certain patient characteristics, underlying diagnosis, and operative techniques.
The biomechanical characteristics of the cervical spine make it particularly prone to postlaminectomy kyphosis. Biomechanical studies indicate that, with a normal lordotic posture, the posterior anatomic elements support 64% of the axial load placed on cervical spine. By comparison, the vertebral bodies support only 36% of the axial load.
In addition to removing supportive anatomic structures, a laminectomy procedure can also result in denervation of the paraspinal muscles. This may potentially lead to muscle atrophy and a subsequent reduction in their stabilizing properties. Denervation of the facet joints can also occur.
Disruption of the supporting posterior elements affects the tension band effect of these structures and allows for a gradual forward angulation of the spinal column. This creates a biomechanically unfavorable environment for the cervical musculature and other supporting structures. As the kyphosis progresses, axial loads increase on the anterior vertebral bodies leading to a gradual worsening of the deformity.
With significant kyphosis, the spinal cord may become “draped” over the posterior margin of the vertebral bodies ( Fig. 34-3 ). This can result in flattening of the small feeding vessels to the cord producing myelopathy. In addition to neurologic dysfunction, patients may experience severe mechanical neck pain caused by facet joint disruption. The deformity may accelerate degeneration of the intervertebral discs, further contributing to the mechanical neck pain. In advanced cases of cervical kyphosis, forward vision, swallowing, and respiration may also be adversely affected ( Fig. 34-4 ).
Postlaminectomy kyphosis can be prevented in most cases. Laminectomy is contraindicated in patients who have a reduction of their cervical lordotic curve with straightening or anterior angulation of the cervical spine. The absence of cervical lordosis on preoperative studies is associated with a twofold increase in the incidence of postoperative kyphosis.
Limiting the disruption of the facet joints during bone removal, correctly applying sound fixation and fusion techniques, and recognizing the need for supplemental anterior column support all minimize the potential for a postsurgical deformity.
INDICATIONS FOR SURGICAL MANAGEMENT
In the event a kyphotic deformity develops after laminectomy, it should be managed aggressively, particularly in those patients who experience intractable pain, radiculopathy, or myelopathy. Although observation and external bracing may be useful in patients with limited kyphosis, surgery is frequently necessary to halt the progression of the deformity and, preferably, correct the sagittal alignment of the cervical spine.
The indications for surgical correction of a kyphotic deformity are a progressive neurologic deficit, functional impairment, and intractable pain. Surgery can be performed through an anterior approach, a posterior approach, or not infrequently, a combined anterior and posterior approach. The combined approach can have a varied sequence but typically consists of an initial anterior approach followed by a posterior approach, or a three-stage posterior, anterior, posterior sequence. Selection of the appropriate surgical approach is dependent on several factors including the extent and severity of the deformity, the flexibility of the deformity, and the location of any neural compression.
Detailed imaging of the kyphotic deformity is critical to the development of a surgical strategy. Plain radiographs with flexion and extension views can show the overall extent of the deformity, the status of the vertebral bodies, and the flexibility of the cervical spine. Magnetic resonance imaging can detail the location of spinal cord or nerve root compression. If further anatomic detail is needed, postmyelography thin-section computed tomography (CT) can be obtained. Reformatting the CT images in the sagittal plane can provide a more accurate assessment of whether the involved facet joints are fused or mobile.
CT images of the deformity can also be transferred to a surgical navigation workstation. This allows for creation of a three-dimensional model of the deformity, as well as visualization of the deformity in multiple planes. Potential screw trajectories can be planned to determine anatomic feasibility (i.e., C1-2 transarticular screws).
Once the appropriate imaging studies have been obtained, the appropriate surgical strategy can be selected. Reasonable objectives of surgery should include removal of any neural compression, as well as correction of the deformity to at least a straightened cervical spine. Surgical correction of a kyphosis by addressing pathology at only a single level is frequently unsuccessful. Typically, a more effective correction can be achieved by regaining a few degrees of correction at multiple spinal levels.
It is important to identify the end vertebrae of the deformity. The end vertebrae are defined as the two vertebrae lying immediately above and below the deformity. The end plates of these vertebrae are either parallel or in extension with respect to the adjacent vertebrae. In most cases, the end vertebrae form the rostral and caudal extent of the surgical reconstruction providing that deformity correction has been achieved. If a suitable correction of the deformity has not been achieved, the reconstruction may need to extend beyond these two vertebrae.
Preoperative management of a kyphotic deformity may also involve the use of cranial traction for up to 5 to 7 days. In selected cases of nonfixed deformities, traction may be able to partially or completely reduce the deformity, allowing for a more conservative surgical strategy. However, traction should not be used in cases of kyphotic deformities with severe ventral epidural compression. Traction in theses cases may exacerbate the epidural compression, resulting in an acute neurologic deterioration.
After obtaining the appropriate imaging studies and determining the flexibility of the deformity, the spinal levels involved, the presence or absence of epidural compression, the potential role of preoperative traction, and the patient’s medical status and ability to undergo major deformity correction surgery, an appropriate single-stage or multistage approach can be planned and carried out.