Cervical spondylotic myelopathy (CSM) is caused by reduction of the sagittal diameter of the cervical spinal canal.
Normally, the canal diameter in the subaxial cervical spine is approximately 17-18 mm in adults, normally.
Cervical myelopathy may result from congenital or degenerative changes in the cervical spine.
It is the most common cause of spinal cord dysfunction in adults older than 55 years, as well as acquired spastic paraparesis or quadriparesis in adults.
Risk factors for cervical myelopathy include: cigarette smoking, frequent lifting, and diving.
There are 5 articulations that comprise the cervical motion segment: the intervertebral disc, the two facet joints, and two false uncovertebral joints of Luschka., that can undergo degenerative changes.
As aging of the spine results in loss of disc height, allowing uncovertebral joints into contact, thereby distorting the normal biomechanics.
Osteophyte formation, ligamentum flavum hypertrophy, and facet/uncovertebral joint sclerosis occur.
Disc space collapse also causes a rostral-caudal translation, which in turn magnifies laxity of the joint capsules and ligamentum flavum with further degeneration.
Degenerative cervical vertebrae changes occur most commonly at C5-6 and C6-7.
Degenerative changes are static factors, a category that also includes congenital spinal canal stenosis and disc herniation.
Dynamic factors, are those that exert abnormal forces on the spinal column during flexion and extension under normal physiological conditions.
Flexion spinal forced can increase spinal cord compression in the presence of disc protrusions or vertebral osteophytes, which in turn causes stretching of the spinal cord.
Extension spinal forces can increase spinal cord compression by infolding of ligamentum flavum or facet joint capsules, which causes shortening and thickening of the spinal cord.
The natural history of cervical myelopathy is one of progressive disability, as neurological function does not return to normal.
Cervical myelopathy may also result from spinal cord ischemia due to compression of spinal arteries, arterial feeders, or obstruction to venous outflow.
A reduction of the diameter of the cervical spinal canal can be a result of spinal cord contusions secondary to trauma, intracanal neoplasia, syringomyelia, and hemorrhage.
Posterior cervical laminectomy, in general, is reserved for patients with predominantly dorsal or circumferential compression, multilevel involvement, and a straight or lordotic spine.
The standard cervical laminectomy does not require fusion, thus preserving motion segments that would be lost in an anterior cervical discectomy and fusion.
Patients who are unwilling to experience limitation to range of cervical motion should be considered candidates for cervical laminectomy or foraminotomy.
No absolute contraindications exist for cervical laminectomy.
Cervical laminectomy should be avoided in patients with a preexisting kyphosis, in children, and in those with significant ventral masses that may cause cord compression if kyphotic deformity develops.
In children and those with kyphosis, the addition of instrumentation and fusion are considered.
The most common neurological deficit following laminectomy is C5 (most commonly) or C6 nerve root irritation causing motor weakness, which has been reported in up to 13% of cases.
Delayed kyphosis following laminectomy may occur in up to 21% of cases.
Infection and wound breakdown may be more common with laminectomy than with ventral procedures.
Reduced mobilization, poor wound care and personal hygiene, and pressure on the incision while lying supine may be associated with higher complication rate.
About 1.3% of patients develop postoperative epidural hematomas, which may be large enough to cause spinal cord compression and secondary neurological deficits.
Cerebrospinal fluid (CSF) leaks can result.
Injury to the spinal cord can occur due to either ischemia caused by blood pressure changes or direct compression of the cord during manipulation.
Useful assistance to cervical spine surgery is electrophysiology neurological monitoring, which can include somatosensory evoked potentials, motor evoked potentials, intraoperative electromyographic responses, nerve action potential monitoring, and direct spinal cord stimulation.
Succinylcholine should be avoided in patients with denervation injury, as it can cause acute hyperkalemia.
Newer muscle relaxants such as vecuronium and rocuronium are suitable alternatives.
Posterior cervical laminectomies are mostly performed in the prone position and less frequently in the sitting position.
After the patient is anesthetized in the supine position, the head is secured before turning into the prone position.
Rigid fixation is preferred in most cases.
The endotracheal tube must be firmly secured and the eyes appropriately lubricated, and protected.
Prone positioning complications include nerve palsies and compression injuries due to inappropriate positioning, exaggerated limb stretch, and inadequate padding.
Sitting position is associated with a higher incidence of venous air embolism, hypotension, and the discomfort experienced by the surgeon: the sitting position is less frequently used today.
Venous air embolism is thought to arise from air that enters noncollapsible veins, dural sinuses, or diploid veins.
Venous air embolism causes pulmonary hypertension with reduction in peripheral resistance, a gradual fall in cardiac output, and subsequent arrest.
Due to paraspinous muscle stripping, patients experience more pain in the immediate postoperative period than preoperatively.
Some patients report that a soft cervical collar helps with maintaining support and decreasing pain.
A midline incision is made and the dorsal spine approached through the subcutaneous tissue along the avascular ligamentum nuchae using monopolar cautery.
Subsequently the paraspinal muscles are stripped from the spinous processes, either bilaterally (laminectomy) for circumferential disease or unilaterally (hemilaminectomy) for unilateral compression or foraminal narrowing.
If C2 is not decompressed , its muscle attachments should remain to provide upper cervical stability.
The laminae with the spinous process attached are removed en bloc.
Not more than 50% of the facet should be removed to prevent joint instability.
Bleeding points from bone are most effectively controlled with bone wax.
Surgicel and Gelfoam act through chemical and direct contact activation of the clotting cascade.
After decompression and hemostasis is achieved, the operative site is irrigated with saline or lactated ringers solution, with or without antibiotics, and the incision is closed in layers and the skin secured with sutures, staples, or skin adhesive.
Clinical outcomes are unsatisfactory in 30% of patients.