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 fusion in addition to laminectomy was a solution in the United States and European countries, whereas laminoplasty was created in Japan, especially for treating ossification of the posterior longitudinal ligament (OPLL). Such ossification is difficult to remove directly via a ventral approach because the extremely hard ossification often tightly adheres to the dura mater. Direct resection of the ossification, therefore, was strongly associated with the potential risk of disastrous cord damage, and postoperative displacement of the grafted bone or pseudarthrosis was not rare, because a long bone graft was needed to span the trough after resection of the long OPLL. All of these complications kept most 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 et al.,¹ 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

The surgical indication for compressive cervical neuropathy is a myelopathy that progresses despite treatment. It is, however, difficult to determine when to apply surgery to cervical myelopathy, because its natural history remains obscure. Apparent ambulatory disturbance is a definite indication, but symptoms no more profound than finger numbness are debatable indicators. Some surgeons prefer the less popular 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 should be discussed in contrast with those for ventral and other dorsal techniques. 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 equal to or less than 13 mm. Because most patients with myelopathy who require surgical decompression have a developmentally narrow canal, they are 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 and/or steep ventral lesions, even after sufficient dorsal space is provided by laminoplasty. Herniated nucleus pulposus, however, is 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 morbidities.

Contraindications

A cervical kyphosis of greater than 5 to 10 degrees is considered a contraindication for laminoplasty, because the spinal cord cannot be released from the anterior lesion if the dorsal space is made by laminoplasty.

Elderly patients who 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.² In contrast, mutilating-type RA and/or RA with vertebral slippage more than 5 mm is 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

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 either 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 following 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 situ by sutures placed between holes drilled in the lamina and the facet joint capsule. Postoperative reclosure of the lamina, however, can take place, and the opening 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. 46-1). 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.

FIGURE 46-1 A, Lateral radiograph after unilateral laminoplasty. B, CT scan after unilateral laminoplasty. A ceramic spacer is fixed between the opened lamina and the lateral mass with a suture.

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 popular 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.

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 kinds of laminoplasties. 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.

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.