Cervical Laminoplasty

Summary of Key Points

•

Laminoplasty is a procedure to enlarge the cervical spinal canal.
•

There are two basic categories of laminoplasty commonly used today: unilateral (hinge) laminoplasty and bilateral (hinge) laminoplasty.
•

The indications of these two kinds of laminoplasties are the same, yet they are similar not only in outcome but also in morbidities.
•

Indications for laminoplasty include narrow spinal canal, spondylotic myelopathy, ossification of the posterior longitudinal ligament, and disc herniation.
•

Laminoplasty is a safe procedure that attains good neurologic results that are long lasting after surgery.
•

C5 palsy and axial pain are two of the biggest problems after laminoplasty.
•

C5 palsy usually spontaneously subsides within 6 months of surgery; however, the origin is not clear.
•

Axial pain can be prevented to some extent by sparing the C7 spinous process from the range of laminoplasty.

General Principles and History

Laminectomy was first introduced to release the spinal cord compressed at multiple levels, although it fell into relative disfavor due to complications such as laminectomy membrane, segmental instability, kyphosis, and late neurologic deterioration. Ventral decompression and fusion or posterior decompression and fusion was a solution pursued in the United States and European countries, whereas laminoplasty was pursued in Japan, especially for treating ossification of the posterior longitudinal ligament (OPLL). This ossification is technically difficult to remove directly via a ventral approach because the ossification often tightly adheres to the dura or involves the dura. Direct resection of the OPLL is associated with the potential risk of cerebrospinal fluid leak and disastrous spinal cord damage, as well as postoperative displacement of bone/cage graft and pseudarthrosis because of long grafts needed to span the decompression trough after resection of long OPLL. These complications kept many surgeons away from employing ventral surgery for cervical OPLL. Laminoplasty was developed as a safer and more reliable procedure to treat OPLL in 1971 by Hattori and colleagues, who expected to enlarge the spinal canal and to relieve neural compression while maintaining a skeletal and ligamentous dorsal arch to prevent epidural scarring and malalignment of the cervical spine. Although this procedure, the so-called Z-shaped laminoplasty, was rather complicated, simpler and more feasible laminoplasty procedures were devised and are now divided into two categories: unilateral (hinge) laminoplasty and bilateral (hinge) laminoplasty. Given that the patients with compressive myelopathy generally have a developmentally narrow spinal canal, decompression over the entire cervical spine with laminoplasty seems more reasonable than ventral decompression surgery, in which operated levels are restricted and adjacent segment disease can take place several years later. Thus, the number of patients with compressive myelopathy who undergo laminoplasty is increasing each year. Several trials to eliminate the disadvantages of laminoplasty are discussed herein.

Indications

A convincing surgical indication for compressive cervical myelopathy is a myelopathy that progresses despite conservative treatment as the result of a congenitally narrow spinal canal, cervical spondylotic myelopathy (CSM), OPLL, and disc herniation. It can be, however, difficult to determine when to apply surgery to cervical myelopathy, because its natural history remains obscure. Apparent ambulatory disturbance (a definite indication) and Nurick grade 2 myelopathy (slight difficulty walking that does not prevent full-time employment) are said most likely to improve from surgery. Symptoms no more profound than finger numbness are debatable indicators. Some surgeons prefer the less common prophylactic laminoplasty to prevent accidental spinal cord injury for patients with a narrow spinal canal even if they have only slight neurologic symptoms. It is, however, difficult to eradicate the risk of spinal cord injury by doing laminoplasty; some patients with OPLL who have residual cord compression after laminoplasty can sustain cord injury due to minor trauma.

Indications for laminoplasty versus other dorsal and ventral techniques can be varied. Generally speaking, a patient with spinal cord compression at one or two levels is a good candidate for anterior decompression and fusion unless the anteroposterior canal diameter is extremely narrow throughout. Many patients with myelopathy secondary to a developmentally narrow canal are good candidates for laminoplasty. Although the spinal cord is assumed to migrate dorsally and escape from anterior lesions by laminoplasty, such a mechanism may not work in two special conditions: kyphosis and the presence of a large anterior lesion. In a kyphotic cervical spine, dorsal cord migration may not be expected after lamina opening, yet some surgeons argue that kyphosis of less than 5 or 10 degrees can benefit from laminoplasty. The extent of kyphosis for which laminoplasty can effectively release the spinal cord remains unknown. The spinal cord does not seem to escape from large or steep ventral lesions, even after sufficient dorsal space is provided by laminoplasty. A herniated nucleus pulposus, however, can be successfully treated by laminoplasty. Neurologic improvement is excellent after laminoplasty for disc herniation, regardless of whether the herniated nucleus is absorbed after surgery. Beak-type OPLL, in contrast, does not seem to be successfully treated by laminoplasty. Resection or floating of the ossification via the anterior approach should be considered for these patients, although these methods are technically demanding and associated with a high rate of surgical morbidity.

Contraindications

A cervical kyphosis of greater than 5 to 10 degrees is considered a relative contraindication for laminoplasty, because the spinal cord cannot be released from the anterior lesion even if sufficient dorsal space is created by the laminoplasty. Elderly patients who can tolerate general anesthesia may be candidates for laminoplasty because the operative impact of laminoplasty is acceptable. There exist, however, arguments regarding the operative outcome for elderly patients. Potential risks for postoperative delirium and cardiovascular accidents should be taken into account.

Subaxial lesions in rheumatoid arthritis (RA) have been treated with arthrodesis, although reduction of neck motion, swallowing disturbance, and adjacent segment disease are not rare after spinal fusion. Laminoplasty is an alternative to diminish the drawbacks associated with arthrodesis. Retrospective investigation in our series revealed that patients with nonmutilating-type RA can benefit from laminoplasty if subaxial subluxation is mild. In contrast, mutilating-type RA or RA with vertebral slippage more than 5 mm is considered a contraindication for laminoplasty. Cervical myelopathy associated with athetoid cerebral palsy may be best treated with laminoplasty combined with fusion. A screw-rod system or a long bone graft spanning all fused levels with a postoperative halo vest is a common technique to attain spinal fusion. Laminoplasty alone has little effect on the myelopathy of athetoid cerebral palsy. Patients undergoing hemodialysis may be candidates for laminoplasty, unless they have destructive spondyloarthropathy, in which spinal instability should be managed by spinal fusion. Pyoderma on the nape skin is a contraindication for laminoplasty, because of the high risk for surgical site infection. Pyoderma is an infectious dermal disease well observed on buttock skin, although head and neck regions may also be affected.

Although laminoplasty was originally developed to treat OPLL, occasional neurologic deterioration is reported immediately after laminoplasty for massive OPLL. The reason for this complication is unclear, but surgeons with expertise have a good reason for choosing ventral surgery for OPLL that has a thickness greater than 50% of the spinal canal.

Techniques

The basic body position for laminoplasty is prone and similar to that for laminectomy. The head is fixed in a neutral or slightly flexed position using a skull clamp. Cervical lordosis can cause laminar overlap, which can interfere with laminar opening and spacer fixation. Lamina exposure is done in the usual manner for a posterior cervical approach. Semispinalis cervicis muscles attached to the C2 spinous process should be preserved as much as possible. To prevent postoperative axial pain, the C7 spinous process should also be preserved if possible (this will be discussed later in the chapter).

Various types of laminoplasty are in clinical use. They are divided into two major categories: unilateral (hinge) laminoplasty and bilateral (hinge) laminoplasty. In unilateral laminoplasty, or open-door procedure, two bony gutters are drilled on each side of the lamina-facet junction. The gutter on one side is cut out and the lamina is opened by elevating this edge, while the gutter on the other side functions as a hinge by allowing gentle fracture. The side to be opened does not depend on the laterality of compression. A left-side opening is generally convenient for right-handed surgeons. The opened lamina is kept in place by sutures placed between holes drilled in the lamina and the facet joint capsule on the hinged side. Postoperative reclosure of the lamina took place in 34% of the patients. The neurologic recovery rate tended to decline in the closure group compared with the nonclosure group during the long-term follow-up period. To avoid reclosure, the opened space may be spanned by a spacer to maintain the enlarged spinal canal. Resected spinous processes or ceramic spacers are often inserted at every two laminae and fixed by sutures between the lamina edge and the lateral mass. The nonfixed laminae are also kept open by a yellow ligament attached to the adjacent fixed laminae ( Fig. 66-1 ). Small metal plates are alternative implants to maintain the opened lamina, although they are not as popular in Japan as in Western countries. Metal plating adds to the complexity of the operation, is time-consuming, and adds to the expense.

With bilateral laminoplasty, or the double-door (French door) procedure, three bony gutters are drilled not only on either side of the lamina-facet junction but also in the midst of the spinous process. After the midline cut is made, each half of the lamina is opened laterally, similar to opening French doors. The lamina was originally kept in situ by inserting a bone graft between each half of the lamina; at present the most common insertion materials are ceramic spacers. Although ceramic spacers are usually fixed by sutures, they often become displaced in the early postoperative period. The more dorsally the spacers are inserted, the more often the spacers become displaced. However, neurologic worsening and neck pain were not associated with displacement of spacers or deformation of the spinal canal.

Although the superiority of unilateral or bilateral laminoplasty has been discussed, significant differences between them have not been found so far. Intraoperative blood loss, operating time, outcome, and morbidities are all supposed to be similar between the two categories of laminoplasty. One more bone gutter to be made in the midst in bilateral laminoplasty seems to be time-consuming for surgeons who prefer unilateral laminoplasty, whereas occasional epidural bleeding from the open side gutter in unilateral laminoplasty seems troublesome for surgeons who advocate bilateral laminoplasty.

When radiculopathy accompanies myelopathy, nerve roots can be released by foraminotomy in addition to laminoplasty. In unilateral laminoplasty, foraminotomy facilitates nerve root exposure on the open side. In bilateral laminoplasty, aggressive foraminotomy might destroy the bony gutter and result in lamina separation. Much care should be taken not to violate the bony gutters. Microsurgical foraminotomy is an alternative method of releasing the nerve roots. Drilling site can be irrigated with abundant cooled water to avoid thermal injury to the nerve roots, which are very close to the bone.

Electrophysiologic monitoring with somatosensory-evoked potentials, motor-evoked potentials, and electromyography is not mandatory for laminoplasty. Inadvertent neural injury cannot be avoided by intraoperative monitoring, and laminoplasty is a relatively safe procedure. Arguments exist over whether electrophysiologic monitoring can detect complications such as C5 palsy. This is doubtful.

During the introduction period of laminoplasty in Japan, a cervical collar was generally applied for a few months after surgery. Surgeons thought that external support was a prerequisite to facilitate bony union of the hinged gutters or grafted bones. However, as unfavorable spine fusion and aggravation of axial neck pain were recognized as the adverse effects of collar application, many surgeons discontinued this practice. In contrast, patients are encouraged to perform isotonic muscle exercises in the early postoperative period to prevent muscle weakness.

Modifications of the Procedure

The rectus major, inferior oblique, and semispinalis cervicis muscles attached to C2 are considered to lend mechanical stability to the cervical spine. These muscles are, therefore, best preserved with laminoplasty, although they often disturb access to the C3 lamina by covering it. Formerly, we cut the tips of the spinous process of the axis along with the origin of these muscles. After opening all laminae, the bony fragments to the axis are replaced so that these muscles can exert traction force again after laminoplasty. Aggressive retraction, but not cutting, of these muscles is an alternative, and some surgeons recommend C3 laminectomy to preserve the muscles attached to the axis.

An additional less commonly performed procedure is disc herniation removal. A disc herniation can be removed dorsally after opening the lamina using the surgical microscope, though conventional laminoplasty is generally done without a microscope. After opening the dorsal dura and cutting the dentate ligaments, the spinal cord can be gently retracted medially. The disc herniation is removed through an incision on the protrusion of the ventral dura, which is easily identified. Cerebrospinal fluid leak is prevented by dura suture in a watertight manner. This procedure may be indicated for a disc herniation with narrow spinal canal.

At the caudal end of a laminoplasty, decompression of the spinal cord can be attained by laminotomy instead of laminoplasty. If a surgeon wants to preserve the lower-most spinous process along with the ligaments and muscles attached to it, the spinal cord is released by drilling off the upper part of the lamina. The significance of preserving the C7 spinous process has gained popularity among surgeons as a method for diminishing postoperative axial pain ( Fig. 66-2 ).