Horsley's posterior decompression, which was first performed 1901, was modified by ScovilIe, Kahn, Fager, and others. The anterior approach to compressive lesions, a more recent development of Robinson, Cloward, and Boldrey, has become increasingly popular. The anterolateral approach offered by Verbiest in 1968 provides a third avenue to the pathologic cervical disc. The plate fixation technique developed recently by Caspar and others has allowed better stabilization after decompression.
ANATOMY & PATHOLOGY
The size and shape of the adult cervical spine vary considerably, not only from person to person but also from vertebra to vertebra, Arnold defined the normal size of the cervical vertebrae, intervertebral discs, and spinal cord. The minimum anteroposterior (AP) dimension of the normal canal is 14 mm at C5 as measured on standard lateral-view roentgenograms. The width of the canal has little clinical significance and is relevant only if a laterally placed mass within it is large enough to compress and displace the spinal cord.
The spinal cord is slightly fusiform in the neck, with its maximal girth at C5. At that level, the average AP diameter of the cord is 8 mm and its width is 13 mm. The maximum normal AP dimension, and therefore the AP diameter the clinician should assume exists, is 10 mm. The remainder of the canal space is occupied by spinal fluid, dura, epidural fat, and epidural veins.
Normal cervical discs are anatomically similar to lumbar discs, consisting of annular and nuclear portions. The nucleus pulposus contains about 88 percent water in infancy, but it gradually dehydrates with age, containing about 65 percent water in the elderly. Clinical syndromes may appear when the nucleus is deformed by either trauma or degeneration. The degree to which the nucleus can be deformed depends on the integrity of the surrounding annulus and the investing ligaments. The average height of cervical discs is roughly 25 percent of the height of the adjacent vertebral bodies and it is variable from one level to other and with aging to become more less.
The eight pairs of cervical dorsal and ventral nerve roots descend slightly to exit from the canal through the intervertebral foramina. The cord moves during flexion and extension of the neck, by as much as 3 mm at the C7 level. The surrounding dura moves slightly more. Cervical roots move in the spinal canal and in the neural foramina, becoming taut with flexion and lax with extension. The angulation of a normal root at the foraminal entrance increases with flexion and decreases with extension.
Dentate ligaments anchor the spinal cord to the dura laterally at intervals, limiting rostrocaudal and side-to-side movement during neck motion. Stress on the lateral columns of the cord during motion is reduced by the fanlike attachment of the ligaments to the cord.
Radicular arteries, originating from the vertebral, thyrocervical, and deep cervical arteries, pass through the neural foramina in the dural root sleeves to reach the anterior and posterior aspects of the spinal cord in company with the dorsal and ventral roots. A confluence of arteries forms ventral to the cord to become the anterior spinal artery. This artery is usually continuous, passing vertically within the ventral sulcus of the cord. Its branches supply the central and anterolateral regions of the cord, including most of the central gray matter. Paired, smaller dorsal arteries supply the posterolateral regions of the cord. Spinal cord veins accompany the arteries, forming radicular veins which pass through the root foramina to join extravertebral venous plexuses.
The dehydration and fragmentation of the nuclear portion of cervical discs with age are natural processes. With aging, some of the vertical height provided by the discs is lost, and the discs lose elasticity. As the disc degenerates, the articular cartilages of the vertebral end plates are subjected to greater stress. Extremes of neck motion become less tolerated. Osteophytic spurs develop around the margins of the disintegrating end plates, projecting as they develop into the spinal canal posteriorly and into the prevertebral space anteriorly. A similar process occurs at the zygapophyseal joints adjacent to the neural foramina. Spurs that originate from the vertebral bodies anteriorly and from the zygapophyseal (apophyseal) joints posteriorly may reduce the size of the neural foramina significantly.
Osteophytes stabilize adjacent vertebrae whose mobility is increased by the degeneration of their common intervertebral disc, and they increase the area of the weight-bearing surface of the vertebral end plates, thereby reducing the effective force on them. The range of motion of the cervical spondylotic spine may be increased if osteophytic bridging is slow to compensate for the degenerating disc, or it may be decreased as a result of spontaneous fusion of osteophytes and adjacent vertebral bodies. Osteophytes may form excessively, projecting into the prevertebral space enough to cause dysphagia or extending laterally to distort the vertebral artery during rotation of the neck.
Ligamenta flava also become inelastic and hypertrophic with age. They stretch over the dorsal aspect of the spinal canal during flexion of the neck, having little effect themselves on its sagittal diameter. The sagittal diameter is reduced overall by flexion, however. With extension, the ligaments fold inward, reducing the AP diameter of the spinal canal. Some degree of compensation is afforded by extension of the neck, since this posture increases the AP diameter of the spinal canal if ligamentous infolding is insignificant. The combined effect of hypertrophic bony ridges at the intervertebral spaces of the spinal canal anteriorly and the infolding ligamenta flava posteriorly is maximal during hyperextension of the neck. Maximum compression of the spinal cord occurs during this posture. The spinal cord moves to and fro over the spondylotic ridges with flexion and extension. Tough dentate ligaments limit that motion, placing local stress on the lateral columns of the cord.
Bone spur formation in a neural foramen is accompanied by dural-arachnoid adhesions and relative entrapment of the cervical root at the site of maximum foraminal narrowing. Motion of the cord with movement of the neck exaggerates the effect of entrapment. The added effect of spine shortening as a result of reduced disc height may further accentuate stress on the root at the foraminal entry zone.
Radicular arteries within the dural sleeves tolerate compression and repetitive minor trauma poorly. In addition, arterial spasm and/or thrombosis may occur at the site of foraminal narrowing. Blood supply to the roots and the cord may be reduced sufficiently to compromise either root or cord function or both. If coexisting vascular disease also reduces the blood supply to the neural structures, the added insult of foraminal narrowing may predispose the patient to clinical symptoms and signs that accompany cervical spondylosis. Venous drainage from the cord may be compromised even more. Osteophytes in the spinal canal and foramina may obstruct thin-walled veins, resulting in raised venous pressure in the cord and subsequent oedema and reduced spinal cord blood flow.
Spinal cords of patients with cervical spondylotic myelopathy and radiculopathy show a variety of gross and microscopic changes. The extent to which the cord is flattened and distorted depends on the severity of canal narrowing and osteophyte formation. Demyelination is most prominent in the lateral columns at the levels of osteophytic bars. Dorsal columns are affected less severely, anterior horn cells are lost, and cavitation in the gray matter may be seen. Cervical spinal roots may be surrounded by fibrotic arachnoid within the dural sleeve. The sleeve itself may be fixed to the walls of the neural foramen.
Rupture of a cervical disc is usually preceded by acute hyperflexion, rotation, or both. The annulus and often the posterior longitudinal ligament tear, allowing the nucleus to herniate into the spinal canal, where it may compress the cord or the adjacent root at its exit foramen. Most often, acute disc rupture occurs laterally in the spinal canal because of the relative weakness of the posterior longitudinal ligament there. Consequently, nucleus herniation causes root compression more often than cord compression. The lower (C4-C7) cervical segments are ordinarily involved. Infarction of the cord and root may follow if compression and ischemia are severe. Acute rupture of the cervical disc with herniation of the nucleus ("soft disc") is rare in patients over 50 years of age. Conversely, disruption of a cervical disc is common in younger patients, particularly those who have sustained fractures, dislocations, or fracture-dislocations.
Unilateral Soft Disc Extrusion
Pain in the neck and arm in a radicular distribution is the hallmark of acute soft disc rupture. Paresthesias may accompany pain but are usually more distal in the extremity. These sensory symptoms are almost always unilateral. Neck mobility is impaired and pain is exaggerated by extension or rotation of the neck. Pain and paresthesias may be reduced by immobilization on the neck. Sensation to pinprick and touch are often impaired in the appropriate dermatome. Weakness with loss of the stretch reflex in the corresponding myotome is typical. Sensory and motor changes are usually simultaneous, but sometimes weakness may be painless, or severe pain may be accompanied by no motor symptoms or signs. Wasting and fasciculations are unusual unless the root compression is prolonged. Long tract signs in the lower extremities are rare.
Central Disc Extrusion with Cord Compression
Central extrusion of the nucleus pulposus into the spinal canal causes compression of the cord to a varying degree, depending on the preexisting size of the canal and the severity of rupture. A variety of spinal cord syndromes may develop. If the cord is severely compressed, paralysis of all sensory and motor function below that level results. The cord is then functionally transected and the spinal cord lesion is called complete. Central disc rupture usually occurs in the lower cervical segments, where flexion and extension are normally more pronounced.
Incomplete spinal cord injury is more common than functional transection after central disc rupture. Among incomplete syndromes seen clinically are the central cord syndrome, the Brown-Sequard syndrome, and the anterior spinal artery syndrome.
Patients with central cord compression typically develop acute, painless weakness in the upper extremities with relative preservation of strength in the lower extremities. Motor reflexes are frequently depressed in the myotomes corresponding to the affected cord level. Loss of sensation to pain and temperature in the arms and hands corresponds to the cervical segments affected. Position and vibratory sensation are usually preserved in all four limbs.
Patients with a Brown-Sequard syndrome demonstrate a loss of pain and temperature sensation on the side of the body contralateral to the cord lesion and loss of motor function on the side ipsilateral to the lesion. Position and vibratory sensation are preserved on the side opposite the injury.
The anterior spinal artery syndrome consists of the loss of all sensory and motor function below the lesion, sparing only sensation mediated by the dorsal columns. Thrombosis of the anterior spinal artery may occur because of central disc herniation.
Acute urinary retention is uncommon in all cervical cord syndromes resulting from a ruptured disc.
Cervical Spondylosis with Radiculopathy
Symptoms and signs of root compression from spondylotic osteophytes may develop insidiously or acutely. While trauma may precipitate the radicular symptoms, usually spondylotic radiculopathy develops episodically and chronically. Bilateral symptoms are uncommon. Because spondylosis may affect more than one cervical segment, symptoms may be more diffuse than those associated with a unilateral soft disc protrusion. Pain and weakness are typical, but one may exist without the other.
Whether root compression is due to an extruded "soft disc" or to a foraminal spur ("hard disc") has little effect on the clinical complex that results. Sensory loss, paresthesias, neck and arm pain, weakness, and hyporeflexia, all in a radicular pattern, stem from compromise of the sensorimotor roots at the intervertebral foramen.
Cervical Spondylosis with Myelopathy
Myelopathy from cervical spondylosis develops episodically and insidiously. The clinical syndromes associated with this disease are similar to those seen with central disc herniation but usually are milder. There may be improvement between episodes, but function rarely returns to normal. The central cord syndrome, described by Schneider, is the most common of the myelopathic syndromes associated with cervical spondylosis and is often preceded by an acute hyperextension injury. To see a case with Brown-Sequard due to PCD C5-6 click here.
Radiologic evidence of cervical spondylosis may be obtained in many persons who have neurological symptoms and signs, and in many who do not. Consequently, plain films showing osteophytes, spontaneous fusions, and hypermobility at some disc spaces must be viewed in relation to the patient's condition. A lateral view of the cervical spine in the neutral position that shows an anteroposterior (AP) diameter of the spinal canal of 13 mm or less strongly suggests that spondylosis plays a part in the patient's neurological syndrome. Oblique views of the cervical spine demonstrate foraminal spurs clearly.
Myelography was the best radiographic test for assessing the site and severity of compression of the cord and roots by spondylotic osteophytes. Lateral, AP, and oblique views from the foramen magnum through C7 are essential for an accurate assessment of the cord and its roots. Myelography is usually combined with CT scanning to improve the visualization of intradural details, particularly of nerve roots.
Computed tomography (CT) delineate the size and shape of the cervical spinal canal in transverse and AP planes. Congenital narrowing and osteophyte protrusion into the canal are well shown by this method. Nerve root and spinal cord details are not seen clearly unless a radiopaque medium has been injected intrathecally.
Magnetic Resonance Imaging
Magnetic resonance imaging (MRI) is the golden standard for the cervical spine, if it was performed by new generations of MRI technologies with skilled technician. It offers remarkable anatomic details, particularly of soft tissues such as the spinal cord, nerve roots, discs, and cerebrospinal fluid. Ligaments, fat, and vascular structures such as the vertebral arteries can also be seen clearly. Bone detail, including fracture sites, is less clearly defined. This imaging modality offers great diagnostic power to clinicians who treat cervical disc disease and has replaced more traditional modalities such as myelography in many clinics. The use of dynamic MRI with the patient setting in the positions, which cause his major complains brought many information , which was lacking in the standard protocols when MRI was performed, with the patient in supine relaxed position.
Electromyography (EMG) is usually helpful in the preoperative evaluation of the patient with radicular symptoms and signs. The test is confirmatory and, when coupled with myelographic or MRI evidence of root compression, is highly specific. However, I seldom refer to EMG. It is in the case that, there are no morphological convincing changes explaining the complains of the patient, or the presence of other pathologies, which could influence the surgical decision and modify the outcome.
Not all patients with radiographic evidence of cervical spondylosis and a clinical syndrome suggesting involvement of the cervical cord or one or more nerve roots have cervical spondylotic radiculopathy and/or myelopathy. Some may have amyotrophic lateral sclerosis, a spinal cord tumor, or a demyelinating disease. Others may have a brachial plexus lesion or even a lesion of one or more peripheral nerves. Occasionally, coexisting disease processes combine to produce symptoms and signs that are consistent with a single lesion, such as cervical spondylotic radiculopathy and tardy ulnar palsy.
Because the differential diagnosis must consider these fine distinctions, patients with cervical spondylosis and a neurological syndrome must be evaluated carefully and completely before therapy begins. The clinical course and its ultimate outcome are sufficiently unpredictable to warrant a cautious approach.
Differentiating between cervical spondylotic myeloradiculopathy and amyotrophic lateral sclerosis may be especially challenging. Both tend to appear in older patients, while almost all older patients have radiographic evidence of cervical spondylosis. Patients with amyotrophic lateral sclerosis usually can be distinguished from those with deficits from spondylosis alone on the basis of clinical findings, particularly fasciculations and wasting in the lower as well as the upper extremities, combined with EMG evidence of denervation.
Medical treatment is basically for the relief of symptoms. Bed-rest, heat application, neck massage, analgesics, and muscle relaxants are all common remedies, particularly for the pain of radiculopathy, Many patients improve with these simple measures. More specific treatment includes immobilization of the neck with a rigid cervical collar and intermittent cervical traction. Generally, halter traction of the cervical spine in either the supine or sitting position will relieve root pain and spasm in the neck muscles. These measures all may be used effectively in outpatients, When the patient fails to respond, hospitalization may be necessary to institute continuous traction and more concentrated physical therapy for a few days.
The presence of a minor or stable neurological deficit in patients with cervical spondylosis does not preclude medical treatment. Frequent evaluation of the patient's progress is imperative to gauge the course of the syndrome. Because the disorder may be episodic, medical therapy is often effective during the symptomatic phase.
It is very important to have the proper clinico-morphological picture of the patient, before starting certain measures of physiotherapy. Traction is contraindicated in patients with huge extrusion and could lead to catastrophic outcome. Over the years, I got the standard policy, to keep the patient in collar with non-steroidals, till the final diagnosis is achieved.
Surgical treatment is generally reserved for those patients with intractable pain, progressive neurological deficits, and documented compression of the cervical nerve roots, the spinal cord, or both. Relief of pain and either stabilization or reduction of the deficit can be expected in most patients treated surgically if they have been judiciously selected for operation.
Sometimes a defect will be confined to a single level or root sleeve corresponding precisely to the clinical presentation. Sometimes the defects are widespread, extending from C3 through C7 with poor clinical localization. And sometimes extensive spondylotic change is accompanied by multiple root compression and canal narrowing.
Surgical treatment consists of decompressing the nerve roots and the spinal cord and removing the offending osteophytes. The approaches to the compressed structures are basically two-anterior and posterior (Fig. 381-71, A posterior approach affords easy access to the posterior elements of the vertebrae and to the dorsal and dorsolateral aspects of the spinal canal and its contents from Cl to Tl. Dorsal compression is best treated by a dorsal approach. Hypertrophic and inelastic ligamenta flava compressing the cord are readily removed by laminectomy. Similarly, decompression of the cervical roots posteriorly is easily accomplished with one or more foraminotomies. If the patient has combined myeloradiculopathy from predominantly posterior compression, then treatment with laminectomy and foraminotomy is effective. The posterior approach, however, has two disadvantages: It probably increases mobility, thereby stimulating further bone spur formation; and it does not afford access to the ventral spinal canal, where the greatest amount of osteophyte formation usually occurs.
The anterior approach to the cervical spine is easy and safe from the levels of C3 through D2, the vertebral segments most often affected by spondylosis. The anterior intervertebral route exposes the vertebral bodies, the discs, and the ventral spinal canal, and, consequently, osteophytes that form in the ventral aspects of the root foramina and spinal canal can be removed directly. The anterior approach has two distinct advantages: Osteophytes can be removed safely, and fusion of the affected disc space provides permanent immobility of that joint. The disadvantages of the anterior approach are that it may cause increased stress on nonfused disc spaces above and below the operated level and that it affords no access to posterior elements that may be compressing the neural structures.
Some surgeons use either the posterior or the anterior approach exclusively. We prefer a more flexible approach, tailoring the procedure to fit the location of maximal compression. If the cord is compressed primarily from anterior osteophytes, the approach is anterior. Conversely, posterior compression, particularly if caused by a congenitally narrowed spinal canal or pronounced infolding of posteriorly situated ligamenta flava, is best relieved by a posterior approach. Because most cord and root compression in the neck occurs from anterior disc fragments, osteophytes, or both, the anterior approach to the cord and roots is used more often.
Patients rarely require external neck support for stabilization after operation, particularly if the procedure has been done without a bone graft. A soft collar may give some relief of remaining symptoms. If a graft has been used, a more rigid external device is warranted.
Anterior Discectomy without Bone Graft
Before anaesthising the patient, he is checked for positions causing to him deleterious effects, to avoid them during anaesthesia. The patient is anesthetized in the supine position and ventilated through a nonkinking endotracheal tube. If the disc to be attacked is at C3-4, then the tube must be inserted transnasally. If other lesions are encountered, then transoral route is the rule. Hallow traction with different weights, depending upon the level of attack is applied, taking into account the preoperative position of the patient, which not causing harm. The chin is kept strictly upward. It facilitate image control for the level count and bring less trauma due to traction during surgery.
The approach may be from either side. To expose only one or two of the vertebrae from C3 through C7, An incision is made 20 mm across the anterior border of the sternocleidomastoid muscle. After transection of the platysma fibers, that muscle is dissected rostrally and caudally to facilitate deep retraction. The anterior border of the sternocleidomastoid can be readily identified, and the veins within the adjacent fascia kept intact. The middle layer of cervical fascia bridges the sternocleidomastoid and the strap muscles of the larynx; it is incised, and the exposure is widened and deepened by blunt and sharp dissection. The carotid sheath and its contents are retracted laterally by finger dissection, and, at the same time, the trachea and esophagus are mobilized medially. The deep cervical fascia overlying the longus colli muscles and the anterior longitudinal ligament of the cervical spine are then visible. Rostral and caudal mobilization of the carotid sheath and tracheoesophageal bundle by blunt and sharp dissection improves exposure.
When the proper level has been verified radiographically, the longus colli muscles are sharply dissected from the vertebral bodies anteriorly and from the adherent annulus of the disc. A selfretaining retractor is applied to the skin and platysma. Deep traction is used by modified blunt rectangular retractors. I used for several years the Cloward retractors, but, for 15 years, I stopped using them and started to use the rectangular simple ones. The advantage is that the assistant, when tired, asking for a relief, is an indicator that relief to the soft tissues is also needed. Using magnifying loupes with the Parallax technology for digital video recording with coaxial illumination, you are able to perform the surgery freely and easily from any angle. Suction-irrigation, bipolar coagulation, microsurgical instruments, and a high-speed drill with a long handle, angled adapter, and a small burr are set in place.
The annulus is incised and the nucleus removed with small straight and angled pituitary. When the posterior aspect of the disc space is reached, exposure of the bone may be expanded by drilling away the remaining cartilaginous end plates, above and below, and some of the cortical bone beneath them. The exposure should not exceed 13 mm in width and 5 mm in height. It may be widened a few millimetres posteriorly to gain easy access to the bone adjacent to the neural foramina. Bone wax very seldom is used.
The posterior margin of the annulus is contiguous with the posterior longitudinal ligament. The ligament may be excised by curettage to expose the dura and the proximal I to 2 mm of the cervical root sleeves laterally if a free disc fragment is suspected. If the ligament is intact, it must be removed all over to ensure that no remnant is left behind.
Free fragments of soft disc material are removed easily. The neural foramina, while not directly visible, are readily palpable with a nerve hook or small, angled curette. Fragments within the foramina can be removed with an angled curette.
If a spondylotic bar projects posteriorly in the midline, it is best removed by microburst of black colour to prevent visual tiredness and optical illusions, proceeding from the midline laterally to the neural foramina. Disc spreader instruments can enlarge the disc space, but we stopped using them 15 years ago, because of their unpredictable traumatic effect. In contrast, increasing the weight of the Hallow traction, can give the desired result and knowing that the big extruded pieces of disc material were removed. Spurs of the uncovertebral joints may project into the neural foramina, where they can be palpated and removed by curettage until the foramina become decompressed. It is important to enlarge the neural foramina generously
if bone grafting is not used. If intervertebral fusion by a bone graft is planned, then the neural foramina need not be enlarged as much, but the graft must distract the vertebral bodies to widen the neural foramina.
During this procedure, the anterior exposure achieved has disturbed neither the lateral margins of the annulus nor the lateral aspects of the vertebral bodies. Most of the nucleus pulposus has been removed, as well as cartilage from two vertebral end plates and some cortical bone from the articular surfaces. The anterior longitudinal ligament and sometimes the posterior longitudinal ligament have been transected, but the uncovertebral joints are essentially undisturbed.
Bleeding is usually 1-2 ml and haemostasis is not required before closure of the wound. A good platysma closure will ensure a narrow scar, and the skin closure with subcuticular suturing completes the procedure.
Some settling of the vertebrae occurs, more anteriorly than posteriorly, after operation without fusion. The neural foramina may become slightly narrower after operation than they were before, unless a proper foraminotomy has been done. But since posterior settling of the vertebrae is slight, the foramina are not narrowed significantly. Spontaneous fusion of adjacent vertebrae can be expected to occur by 3 months after operation.
Anterior Discectomy with Bone Graft
Both the Cloward and the Smith-Robinson techniques employ placement of a bone graft, usually from the ilium, into the evacuated disc space. Most neurosurgeons remove osteophytes from the spinal canal and foramina by curettage before fashioning the disc space for the bone graft. The operating microscope provides good light and some magnification for this stage of the procedure.
The depth of the interspace is measured, and the drill guide, seated over the disc space, is set to the measured depth. The drill is then fitted into the drill guide and a hole made overlying the empty disc space, taking care to preserve the posterior cortical rim of the adjacent vertebral bodies. If more than one disc is to be resected and grafted, the smallest drill and corresponding bone dowel should be used. The dowel is inserted into the hole prepared for it and gently impacted there so that the two cortical surfaces of the dowel are anterior and posterior.
The bone graft is obtained from the ilium. An incision is made just below the iliac crest. The crest is exposed and the muscles on its anterior surface stripped free. The Cloward bone dowel cutter is passed transversely through the ilium, leaving the crest intact. Several dowels may be obtained if necessary.
This procedure is similar to the Cloward method except that iliac crest bone with a cortical surface on three sides is fashioned precisely to fit the intervertebral space. It is thus possible to position the graft so that it rests on the posterior lip of cortical bone of the adjacent vertebral bodies and is countersunk beneath the anterior edges of the vertebral cortical bone. The bone graft itself is obtained from the exposed iliac crest with high-speed drilling tools. Little or no muscle dissection is necessary. Postoperative roentgenograms are made after anterior discectomy with or without bone graft fusion to assure proper alignment. Patients usually prefer a semirigid cervical collar for comfort for 2 or 3 weeks. If a bone graft has been inserted, use of a cervical collar for 8 to 12 weeks is advisable.
Anterior Cervical Instrumentation
The goals of internal metallic fixation, as an augmentation to anterior cervical fusion are (I) to improve the fusion success rate, (2) to decrease the incidence of graft extrusion, (3) to maintain proper spinal alignment, and (4) to decrease or eliminate the need for external orthotic immobilization.
The application of the osteosynthetic plate technique to the stabilization of the anterior cervical spine is now in wide application and even overused. In the cervical spine, a rigid plate placed anteriorly provides a construct that resists a variety of potential distortional forces, including flexion and extension as well as rotational and laterally applied forces. In addition when the bone graft beneath the plate is held in contact under load, the plate becomes part of the loadbearing cross-sectional area, thus adding to stability.
Several authors have described the use of osteosynthetic plates for anterior stabilization of the cervical spine. However, this technique did not gain wide acceptance among neurosurgeons until a complete system for anterior plate fixation was introduced by Caspar and co-workers. Properly applied, anterior plating systems provide immediate additional segmental cervical stability, often eliminating the need for extensive postoperative external immobilization.
Single-level anterior interbody discectomy and fusion in the treatment of cervical disc disease and spondylosis has a high degree of success, and the addition of internal fixation is rarely indicated. However, following multilevel discectomy or corpectomy, fusion may be improved significantly by the addition of internal fixation. Also, the surgical treatment of cervical flexion deformities, whether postoperative, posttraumatic, or idiopathic, has been improved by the use of anterior cervical osteosynthesis techniques. Revision procedures for failed previous anterior fusions may also have an improved success rate when supplemented with internal fixation.
Decompressive Laminectomy and Foraminotomy
Several authors describe the posterior decompression of the cervical spinal cord, the nerve roots, or both may be done with the patient in the prone or sitting position. The decision to perform simple laminectomy, foraminotomy, or both depends entirely on the clinical symptoms and signs for which the operation is planned. Compressive myelopathy in the absence of root compression is best treated by a laminectomy, including one additional segment above and below the site of obvious compression shown myelographically. Root compression in the absence of cord compression is best handled by simple foraminal enlargement at the involved level. Sometimes, particularly in older patients, a combined procedure including laminectomy and foraminotomy is preferred. In short, the posterior approach for decompression must be planned as precisely as clinically possible to relieve compression where it is known to exist from all the preoperative testing.
A midline incision is made to expose the spinous processes. The identity of the vertebral segments exposed is confirmed either by palpating the large spinous process of C2 and counting down from there or by taking a lateral x-ray film of the cervical spine. The paraspinal muscles are stripped away subperiosteally so that the laminae and the facets are completely exposed. The spinous processes, laminae, and ligamenta flava are then removed with either rongeurs or a high-speed drill. Whether to start in the midline or laterally is a matter of personal preference. It is best to start at the lowest level that is comfortable, proceeding rostrally in a segmental fashion. Care must be taken not to compress the already compromised dural sac. Instruments that compress the dura significantly during removal of the laminae should be avoided. Epidural fat is usually absent because of the lack of space within the spinal canal. The laminectomy must be wide enough to demonstrate the posterior and posterolateral aspects of the dural sac. Dural root sleeves may be just visible where they emerge from the lateral margins of the dural sac. Haemostasis is achieved with cautery, bone wax, Gelfoam (absorbable gelatin sponge. Foraminal enlargement may follow the laminectomy or precede it. The procedure is easier after laminectomy because the root foramina can be easily localized after the spinal canal has been opened. On the other hand, foraminotomy with rongeurs, curettes, and a high-speed drill with the spinal canal still unexposed assures that the cord will not be accidentally injured in the process of unroofing the neural foramen. We prefer to do the laminectomy first and then the foraminotomy if both are indicated. Foraminal enlargement must extend I full centimetre lateral to the lateralmost margin of the spinal canal to assure complete decompression. Offending spurs or soft disc fragments can be removed readily with small Epstein curettes, but only after the foramen is opened widely enough to expose both the inferior and the superior pedicles that mark the rostrocaudal limits of the foramen.
An extensive laminectomy (C2-C7) coupled with bilateral foraminotomy at multiple levels achieves excellent decompression of the roots and cord. Because part of the facets overlying the foramina are, of necessity, removed, vertebral segment motion may be increased. Subluxation may occur if more than the medial one-third of the facet joint is removed.
Several authors also consider, if the clinical symptoms and signs and preoperative tests indicate radiculopathy without myelopathy, segmental hemilaminectomy and foraminotomy provide excellent decompression. The procedure is similar to that described for complete laminectomy except that the paraspinal muscles are stripped away on one side of the spinous process only and the spinous process remains intact. Foraminal spurs or impacted soft disc fragments responsible for root compression are then removed by the method described earlier.
In general references cervical root compression can be relieved with resolution of symptoms and signs in 80 percent of patients, provided the preoperative diagnosis is accurate and the operation is done carefully from either an anterior or a posterior approach. Myelopathy responds less well to decompression, whether done anteriorly or posteriorly; about 60 percent of patients will improve after operation. Intervertebral fusion occurs after anterior discectomy in most patients, whether or not a bone graft has been used. Instrumentation to fix the graft improves the fusion rate even more.
Complications of the various procedures can be predicted. Root and cord signs may be increased regardless of the approach if the operation is done carelessly. Anterior approaches to the cord and roots may be accompanied by carotid or vertebral artery injury, recurrent laryngeal nerve palsy, oesophageal perforation, or airway obstruction. A postoperative infection or heamorrhage may also result. If a bone graft is employed, it may migrate either anteriorly or posteriorly. Posterior displacement may result in cord compression. Bone graft harvesting from the ilium may result in a painful wound, bowel perforation, or infection at the second operative site.
The posterior approach has fewer inherent risks because fewer vital structures are encountered during the operation. However, extensive removal of posterior bone and ligament increases the mobility of the cervical spine and may contribute to a continuing spondylotic process. Subluxation occurs after an extensive posterior procedure in up to 10 percent of cases