Chapter 44 Cervical Laminectomy and Laminoforaminotomy
Cervical spondylosis, disc herniation, and allied pathologies are a common cause of neurologic compression. Cervical spondylotic myelopathy is the most common cause of spinal cord dysfunction in adults.1
In spite of more than 40 years of evaluation of various techniques, there is no class I or class II evidence to strongly support one procedure over another, be it anterior or posterior, in the overall group of patients.2 The natural history of the compressive myelopathies varies, eroding the efficacy of procedural long-term outcomes.1 The origin of cervical spondylotic myelopathy appears to originate from two principle forces on the spinal cord and associated structures:
In essence, the compressed spinal cord is stretched, or distracted, through a compromised canal, leading to damage in the spinal cord. Interestingly, the damage is often in the lateral cord region in early to moderate cases of myelopathy.4 It has long been felt that, given the frequent ventral location of the compressive spur, the procedure must be directed to that location. It appears that it is the combination of compressive and dynamic motion of the spinal cord that leads to compromised function. In light of the static (compressive) and dynamic forces involved in the genesis of myelopathy, all the ventral and dorsal surgical options that address either one, or both, of the involved factors have a role.4,5
Given the preceding two underlying factors (compression and motion) in the genesis of cervical spondylotic myelopathy (CSM), a wide variety of procedures are available to address the problem. As a primary goal, decompression should be achieved (i.e., the spinal canal volume enlarged). This can be accomplished with anterior discectomy-spurectomy and fusion, anterior corpectomy and fusion, cervical laminectomy, cervical laminoplasty, and cervical laminectomy and fusion.2–6 Each procedure has its attendant downside in the form of various complications. All have been shown to be effective and in the overall population of CSM patients, but no one procedure has clearly outclassed the other options.2 Cervical laminectomy for decompression of the spinal cord and/or nerve roots has been shown to be effective in the treatment of CSM.2,7 It addresses the compressive forces in CSM, but does not reduce the dynamic forces. Nevertheless, many patients do well with this option, and in appropriately selected patients the procedure is a safe, relatively simple, and effective option. A number of advantages can be ascribed to cervical laminectomy/decompression:
• May represent same risk of delayed kyphosis over time secondary to loss of the posterior tension band (lamina and intraspinous ligaments).8 The exact incidence of postlaminectomy kyphosis is not well established, and the published reviews have generally been limited in patient numbers. Clinically relevant, as opposed to radiographically identified, incidental sagittal balance change is probably in the 5% to 10% range.8 This problem, to some degree, can be limited by proper technical performance9 (see section on technique).
• In light of the preceding point, cervical laminectomy should be limited to patients with reasonable lordosis, and not utilized in those with a frank kyphosis. Patients younger than age 20 are at greater risk for delayed cervical kyphosis after laminectomy.7,8
• In patients with advanced CSM, reducing the dynamic component of CSM by adding simultaneous dorsal instrumentation (arthrodesis may be beneficial, but at the time of this writing, the exact subgroup to benefit from this is uncertain).2,5
Cervical laminectomy addresses the compressive aspects of CSM and associated disorders, but not the dynamic forces.2,5,7 If concerns arise regarding frank stability, or it is felt that the dynamic aspects must be addressed, simultaneous dorsal instrumentation and fusion can be utilized in addition to simple decompression. The decision to select one posterior option or another, and even the consideration of anterior options, is often a combination of science and surgeon preference and experience.2,5,7 Over the years, and over the course of 400 cases, I have used the following general guidelines:
• In cases where decompressive laminectomy alone is used if an early to moderate myelopathy is present, but not dramatic signal change within the spinal cord on MRI (myelomalacia). In advanced cases of CSM, I generally favor simultaneous reduction of motion/dynamic forces by adding dorsal instrumentation (lateral mass screws) and fusion to the procedure. This preference is based on outcome trends, and no strong scientific data exist to bolster any dogmatic decision.
1. Prone—The patient is placed on appropriate padding material. The head is fixed in neutral position. Care must be taken to get a solid purchase in bone with the head holder because the weight of the head and neck in the prone position can lead to slippage with attendant lacerations and head shift. It is important to flex the knees to prevent migration of the patient on the table, which can lead to neck extension if the patient slides down the table during the procedure.
2. Sitting—Over the years, the trend had been to avoid the sitting position as inherently hazardous because of the risk of air embolization.10,11 Recently, a trend back to this option has been noted. Although air ingress can be seen in 5% to 8% of the sitting cases, clinically significant air embolization in sitting cervical cases is unusual.10,11 The risk of air embolization in cranial cases is higher because of the noncollapsible venous structures of the cranium. Over 1500 sitting cases accumulated in the literature attest to the safety, with proper technique, of the sitting position.10,11 The sitting position provides a fairly bloodless field due to dependent flow of blood to the bottom of the field and reduced epidural venous tension. Nerve root decompression via dorsolateral foraminotomy can be facilitated for this reason in the sitting position.