S. Tim Yoon and James S. Kercher
DEFINITION
Cervical laminoplasty is a surgical procedure designed to decompress the spinal cord from a posterior approach. The cervical laminae are reconstructed to create more available space for the spinal cord while at the same time preserving motion and normal alignment.
Cervical myelopathy is pathologic spinal cord dysfunction due to spinal cord compression. Compression of neural elements results in a spectrum of cord dysfunction ranging from mild to quite severe. Cervical laminoplasty is most often used to treat cervical myelopathy associated with multilevel cervical stenosis.
Multilevel cord compression is commonly due to cervical spondylotic stenosis. This is a degenerative process resulting in decreased space available for the spinal cord, with possible instability and loss of lordosis. Congenital stenosis of varying degrees is often associated with patients with symptomatic cervical spondylotic myelopathy.
Other conditions such as ossification of the posterior longitudinal ligament, trauma, infection, and neoplasm can result in stenosis that can be treated with laminoplasty.
The key to treating this condition is to achieve multilevel decompression that alleviates circumferential compression and allows the spinal cord to drift away from ventral compressive lesions.
ANATOMY
The cervical spine is composed of seven vertebrae normally arranged in an overall lordotic alignment. The occiput–C1 articulation is responsible for 50% of neck flexion and extension and the C1–C2 atlantoaxial articulation is responsible for 50% of total rotation. Lateral bending below the C2–C3 level is coupled with rotation due to the 45-degree inclination of the cervical facet joints.
The subaxial vertebral segments of C3–C7 are similar to each other and distinct from C1 (atlas) and C2 (axis). The subaxial vertebrae articulate via zygapophyseal or facet joints posteriorly and laterally via the uncovertebral joints, or joints of Luschka.
Intervertebral discs are located between vertebral bodies of C2–C7. The discs are composed of an inner nucleus pulposus and outer annular fibrosus.
Anteriorly the spinal canal is bounded by the vertebral bodies, the intervertebral discs, and the posterior longitudinal ligaments; laterally and posteriorly by the vertebral arch; and posteriorly by the ligamentum flavum, which runs from the anterior surface of the superior lamina to the posterior surface of the inferior lamina (FIG 1).
PATHOGENESIS
Cervical spondylotic myelopathy is the most common indication for cervical laminoplasty. It is the most common cause of myelopathy in patients older than 50 years. By age 40, most people will have radiographic evidence of degenerative changes.3
The degenerative process typically begins in the intervertebral disc. The degenerated discs are more fibrotic as a result of proteoglycan loss within the nucleus pulposus. This is associated with lost water content from the nucleus pulposus and loss of normal shock-absorbing capacity.
With disc degeneration, the disc height decreases and the annulus fibrosus bulges radially, resulting in ventral spinal canal narrowing. Collapse and loss of lordotic curvature can lead to a cascade of compensatory changes, including osteophyte formation around the uncovertebral joints, the facet joints, and the insertion of the annulus fibrosus. In the dorsal spinal canal, there is thickening or buckling of the ligamentum flavum, which causes a decrease in canal and foraminal dimensions.
Protruded disc material, osteophytes, and thickened soft tissues within the canal or foramen result in extrinsic pressure on the nerve roots or spinal cord.
Spondylotic changes and osteophyte compression may also impair the circulation within the cord, leading to cord ischemia and resultant myelopathy.
NATURAL HISTORY
The true natural history of cervical spondylotic myelopathy is difficult to discern. This is due partly to the fact that most cases now are treated surgically and early studies of the disease took place several decades ago. At that time modern diagnostics were unavailable; therefore, confounding variables due to other neurologic conditions cloud the picture.
What is known about the natural history is that the disease process progresses in a variable and unpredictable manner. Often there is stepwise deterioration of neurologic function, with periods of stable symptoms followed by decline.
The clinical course may wax and wane over a period of years. Sensory symptoms may be transient, but motor symptoms tend to persist and progress. While surgical intervention may relieve symptoms and halt progression, some neurologic deficits are permanent and do not respond to surgical treatment.4
PATIENT HISTORY AND PHYSICAL FINDINGS
The diagnosis of cervical myelopathy may be difficult to make due to the variability in clinical findings. Pain is frequently not a significant complaint in myelopathic patients unless associated with root compression or facet arthrosis. Patients may present with subtle findings or profound neurologic deficits.
The diagnosis requires a high index of suspicion and careful evaluation of the patient's history, physical examination, and imaging studies.
FIG 1 • Anatomy of cervical vertebrae.
Patients commonly present with insidious onset of gait disturbance, trouble with balance, and clumsiness in the hands and lower extremities. They may report burning pain in the upper extremities, difficulty in handwriting and fine motor control, diffuse numbness, and weakness of grasp. Advanced cases can present with flaccid weakness and bowel and bladder dysfunction.
The physical examination should begin with an assessment of gait, which may be wide-based, hesitant, stiff, or spastic. Patients may be unable to perform heel-toe walk or may have poor balance during toe raises. A careful neurologic examination should follow. Each dermatome should be tested.
Sensory findings may be variable. Pain, temperature, and vibratory and dermatomal sensation may all be decreased.
On the motor examination, depending on the level of cord compression as well as nerve root and peripheral nerve dysfunction, mixed upper and lower motor neuron findings may be present in the extremities. Patients may have weakness and atrophy as well as brisk reflexes.
The Lhermitte sign is said to be positive when extremes of neck flexion or extension result in paresthesias and weakness. This can be a sign of posterior column compression. Pathologic reflexes such as the scapulohumeral reflex (indicates compression above the C3 level), inverted radial reflex (indicates compression at the C5 to C6 levels), the Hoffman sign, clonus, the Babinski sign, and finger escape may be present.
IMAGING AND OTHER DIAGNOSTIC STUDIES
Plain AP and lateral radiographs are useful for initial evaluation of cervical spine sagittal alignment and the extent of spondylotic changes such as disc space narrowing, osteophytes, kyphosis, joint subluxation, and spinal canal stenosis (FIG 2A).
Flexion and extension views can provide information about possible spinal instability.
Magnetic resonance imaging (MRI) aids in determining accurate dimensions of the spinal cord and canal. MRI is also the technique of choice for visualization of soft tissues such as ligamentous hypertrophy, disc herniations, and changes within the cord parenchyma such as edema and myelomalacia (FIG 2B).
Computed tomography (CT) with and without contrast is superior to MRI for defining the bony anatomy and is the study of choice for evaluating ossification of the posterior longitudinal ligament (FIG 2C,D).
FIG 2 • A. Preoperative lateral cervical spine radiograph demonstrating spondylotic changes: diffuse disc height loss and osteophyte formation. B. Sagittal T2-weighted MRI showing multilevel cervical disc protrusions and circumferential stenosis at C3–4, C4–5, and C5–6, resulting in cord deformation. Cord signal changes can be seen at C3–4 and C4–5, indicative of cord damage. C. Sagittal CT reconstruction showing large ossified posterior longitudinal ligament extending from C2 to C6. There is evidence of failed anterior decompression by an outside facility. D. Axial CT image demonstrating vertebral canal compression from large ossified posterior longitudinal ligament.
DIFFERENTIAL DIAGNOSIS
Cervical spondylosis
Soft disc herniations
Infectious discitis or epidural abscess
Muscular dystrophy or dystonia
Loss of normal sagittal alignment
Neurogenic disorders (syringomyelia, multiple sclerosis, amyotrophic lateral sclerosis, cerebellar dysfunction)
Instability of the cervical spine can cause myelopathic symptoms.
Ossification of the posterior longitudinal ligament
Peripheral neuropathy or nerve injury
Drug intoxication
Vascular disease
Autoimmune disorders
SURGICAL MANAGEMENT
Laminoplasty was specifically designed to prevent the kyphotic deformities seen with laminectomy alone and is associated with fewer complications than laminectomy and fusion.1
Laminoplasty involves posterior decompression from C3 to C7, allowing for dorsal cord expansion and drift while preserving motion.
Indications
Cervical spondylotic myelopathy involving three or more disc levels
Congenital stenosis of the spinal canal
Ossification of the posterior longitudinal ligament
Spinal cord tumors
Contraindications
Kyphotic sagittal alignment of more than 10 to 14 degrees can lead to worsening of the kyphotic deformity and poor neurologic outcomes.
Significant segmental instability
Relative contraindication.
Ossification of the ligamentum flavum. This condition is associated with dural adhesions, which can make opening the posterior arch difficult.
Previous posterior cervical surgery such as foraminotomies. Scar formation can produce adhesions that can make opening the laminar arch difficult.
Primary axial neck pain in the setting of myelopathy. Laminoplasty preserves motion, and hence the procedure is not designed to address pain generation from facet arthrosis and disc degeneration. Fusion procedures provide greater benefit to patients with significant complaints of axial neck pain.
Preoperative Planning
The patient's history, clinical examination, and imaging studies should be thoroughly reviewed and documented before the case.
Evaluation of the patient's active range of motion in flexion and extension assists with head positioning. Passive flexion and extension outside of this range (eg, during positioning) can be dangerous in the setting of cord impingement.
The presence of preoperative axial neck pain may be an indication for an alternative procedure, as listed above.
Careful examination of CT scans to determine the bony anatomy of the dorsal cortices can be helpful. Special attention should be given to the lamina-to-lateral-mass junction.
If concomitant fusion is planned, the midline splitting laminoplasty (“French door”) approach may be considered, but a unilateral open door technique can also be used with fusion and lateral mass instrumentation.
Positioning
Intubation is preformed with caution to protect the cervical spine. This includes advanced notification to anesthesia personnel of spinal cord compression in severe cases. Care should be taken not to extend the neck more than the patient's comfortable range of motion before sedation. The use of fiberoptic assistance should be considered in high-risk cases.
Application of a Mayfield head holder reduces risks to soft tissues and provides a stable platform for the head during the procedure (FIG 3A).
The patient is placed prone onto chest bolsters. The abdomen should be as free as possible to reduce venous bleeding and prevent ventilatory difficulty. Arms are tucked in at the patient's side (FIG 3B).
The head is positioned to allow for slight cervical flexion to tension skin on the posterior neck folds and decrease shingling (or overlap) of lamina. Intraoperative repositioning of the flexion–extension of the head is possible if necessary with the Mayfield tongs.
The bed is then placed in reverse Trendelenburg to decrease venous bleeding and allow for horizontal positioning of the cervical spine.
Spinal cord monitoring is routinely performed in myelopathic patients. This helps to monitor neurologic problems related to positioning as well as with the laminoplasty procedure itself.
The surgical field should be prepared from the nuchal line to roughly T4 to allow for possible wound extension.
Approach
A posterior midline incision is made over the spinous processes from C2 to T1. This can be extended to the occiput or further down the thoracic spine as necessary.
FIG 3 • A. The patient's head is placed in a Mayfield head holder. B. The patient is placed prone onto chest bolsters with arms tucked in at the sides. The head is placed in slight flexion. Spinal cord monitoring equipment is also seen.
TECHNIQUES
INCISION AND DISSECTION
A posterior midline approach to the spinous processes is made, using a longitudinal incision from C2 to T1.
Electrocautery is used to divide the subcutaneous fat in the midline to reach the tips of the spinous processes.
Once the tips of the spinous processes have been found, a subperiosteal dissection is performed to expose the C3–C7 lamina. Careful attention should be taken to stay in the midline avascular plane to reduce bleeding.
The dissection should extend laterally to fully expose the junction of the lateral mass and the lamina.
Exposure should not extend beyond the midportion of the lateral masses.
The extensor muscle attachment to the C2 spinous process is carefully preserved. The inferior C2 laminar margin is usually broad and should be exposed to aid in visualization of the C2–3 junction.
The spinous processes can be amputated at their base. Spinous processes are useful for bone graft (either for strutting open the lamina or for local bone graft for the hinge side).
Removing the spinous processes significantly improves exposure and reduces asymmetric posterior displacement of paraspinal musculature (TECH FIG 1A).
The interlaminar ligamentum flavum between C2–3 and C7–T1 is removed. First, a rongeur is used to create a small opening in the interlaminar ligament flavum. Then a combination of curette and Kerrison rongeur is used to divide the rest of the interlaminar ligamentum flavum (TECH FIG 1B).
TECH FIG 1 • A. Lamina exposure after subperiosteal dissection and spinous process removal. The dissection should extend laterally to expose the junction of the lateral mass and lamina. Attempts should be made to minimize disruption of the facet capsule. This will decrease longterm postoperative neck pain. Planned lines for opening and hinge trough creation have been marked using electrocautery and marking pen. B. A Kerrison rongeur is used to divide the interlaminar ligamentum flavum.
TROUGH PREPARATION
Open-Side Trough
A 3.0 or 4.0-mm round or oval low-aggression highspeed burr is used to form the trough.
The trough location is at the junction of the lamina and lateral mass.
For the opening side, bony layers should be removed in sequence: the outer cortex, next the cancellous middle layer, followed by the ventral cortex (TECH FIG 2A).
Troughs should be made no deeper than 4 mm. Once at that depth, the burr should be directed medially to avoid the facets. Switching to a 3.0-mm burr can be beneficial after the initial work with the 4.0-mm burr to aid in more precise burring.
As the bone is thinned, the surgeon should use a delicate instrument such as a microcurette or Penfield elevator to palpate and identify any bone bridges still attaching the lamina to the lateral masses. Completion of the bone separation can be performed with a microcurette, a 1.0mm Kerrison rongeur, or a diamond burr (TECH FIG 2B).
Care should be used at this time to avoid the epidural veins, which create significant bleeding. Bipolar electrocautery can be used to control bleeding epidural veins.
French Door (Midline Splitting)
The French door technique involves creation of a midline opening trough and two hinge troughs.
The midline of the posterior arch can be split by a variety of methods. One method is to remove the spinous process as described above and use a 4.0-mm lowaggression burr to create a complete midline trough. The burr is carefully manipulated to remove the dorsal midline bone down to the ventral bone (TECH FIG 3).
Completion of the opening is then performed as described earlier and shown in Techniques Figure 2B.
TECH FIG 2 • A. Creation of the opening trough requires sequential removal of bony layers. Figure demonstrates burring with irrigation and suction. B. After the initial burring, completion of the bone separation on the opening side can be performed using a microcurette, a 1.0-mm Kerrison rongeur, or a diamond burr. Figure demonstrates the careful removal of the opening trough ventral cortex with the use of a microcurette during a midline splitting French door laminoplasty.
Hinge-Side Trough
The hinge side is prepared opposite the opening side at the same anatomic junction of lamina and lateral mass.
The hinge trough is prepared in a similar manner; however, it entails removal of only the dorsal cortex and cancellous layers. The ventral cortex can be thinned to open the hinge, but the surgeon should preserve as much as possible to preserve a mechanically sound hinge (TECH FIG 4).
Stiffness of the hinge should be tested periodically during preparation. This is the rationale for performing the hinge after the open side has been completed. The goal is to create a pliable yet firm hinge that yields to moderate opening force without breaking the hinge inner cortex.
Hinge troughs used for the French door technique are prepared in the same anatomic location as troughs created for the open door technique. Similar to the open door technique, ventral cortex should be preserved to create stable hinges.
TECH FIG 3 • The French door technique uses a midline opening trough. Here the midline trough has been created. Planned lines for the hinge troughs are shown on either side.
TECH FIG 4 • Opening and hinge troughs for the open door technique. Preserved ventral cortex for the hinge trough is seen at the tip of the Penfield dissector.
OPENING THE LAMINOPLASTY
Proceeding from caudal to cranial, a nerve hook or curved curette is used to elevate the lamina on the opening side. Division of the residual ligamentum flavum and epidural veins proceeds from C3 to C7. A Kerrison rongeur can be used to divide ligamentous attachments, and bipolar forceps are used for cauterization of epidural veins.
The laminae are then opened sequentially. This can be done with the assistance of a curved microcurette to raise the opening side and gently bend open each lamina hinge. Care should be taken to identify and lyse any epidural adhesions (TECH FIG 5A).
Starting from C3 and proceeding to C7 allows for blood to flow away from the working area and reduces the overhang of the inferior edge of the superior lamina due to lamina shingling.
Completion of opening laminae is carried out carefully with small curettes (TECH FIG 5B).
TECH FIG 5 • A. Completing the opening for the French door technique. With the assistance of a curved microcurette, the lamina is gently bent back upon its hinge. Care should be taken to identify and lyse epidural adhesions. B. Completion of open door laminoplasty.
POSTERIOR ARCH RECONSTRUCTION
The laminoplasty door is held open using a variety of techniques.
Plate reconstruction has become popular because of the immediate mechanical security that plates provide (TECH FIG 6A,B). However, eventual mechanical stability relies on hinge-side bony healing to permanently hold the posterior arch open.
Bone struts can also be used; this was the most frequently used method for many decades. Autogenous spinous process grafts fashioned from the spinous processes of C6 and C7 can be used, as well as rib allograft or machined cortical grafts (TECH FIG 6C).
Reconstruction with bone has the advantage of allowing for full bony reconstruction of the lamina arch, as the bone struts usually fully incorporate with time. Furthermore, placing bone is easier and faster to place than plate and screws, but bone provides less initial mechanical stability to the arch and may (rarely) dislodge before healing of the hinge.
Hybrid reconstruction with alternating plate and bone graft can also be used (TECH FIG 6D).
With the French door technique, midline plates can be applied. Other structures have been used, including autograft, allograft, or hydroxyapatite (TECH FIG 6E).
Alternatively, the lamina can be held open with sutures that go from the lamina to the lateral mass or facet capsules. Suture anchors have also been used.
TECH FIG 6 A,B. • Open door plates. A. First, the lateral mass screw is placed with a 6-mm screw. B. Then the lamina is opened and held in place by subsequent 4-mm screws placed in the lamina. C.Machined cortical allograft. Grooves allow for better stability when interpositioned between lamina and lateral mass. D. Postoperative lateral radiograph after laminoplasty performed with alternating plate and graft technique. E. French door posterior arch reconstruction using midline plates. Adequate space must be maintained between the plate and cord to allow for expansion.
WOUND CLOSURE
A deep drain is placed, followed by a layered fascial and subcutaneous closure.
Skin is closed using a subcuticular stitch.
POSTOPERATIVE CARE
Typically a soft cervical collar is worn for comfort.
Most patients can begin immediate active range of motion.
Drain output is monitored and drains are typically removed by 48 hours after surgery.
The patient is weaned from the cervical collar over 2 to 4 weeks.
OUTCOMES
Cervical laminoplasty is a valuable treatment option for myelopathic patients with multilevel stenosis. It provides cord decompression while preserving motion.
With proper patient selection, neurologic outcomes are excellent, with few complications. In a meta-analysis of results on neurologic improvement, 80% of postoperative patients were reported to have excellent outcomes.2
When compared with laminectomy with fusion, outcomes regarding neurologic improvement were similar. However, laminectomy with fusion had more frequent complications, such as progression of myelopathy, nonunion, instrumentation failure, development of a significant kyphotic alignment, persistent bone graft harvest site pain, subjacent degeneration requiring reoperation, and deep infection.1
COMPLICATIONS
Segmental nerve root palsy: This is most commonly a motor deficit affecting the C5 root that occurs a day or two after surgery. It usually resolves to a large degree with time.
Axial neck pain has been reported. However, the pain is typically mild and often described as stiffness.
Loss of cervical motion: Up to 50% loss of range of motion has been reported with some laminoplasty techniques.
Dural tears are infrequent. They can be handled with either direct repair or with fibrin glue with the addition of a lumbar diverting cerebrospinal fluid drain.
The infection rate is very low. Good hemostasis and irrigation is recommended.
REFERENCES
1. Heller JG, Edwards CC II, Murakami H, et al. Laminoplasty versus laminectomy and fusion for multilevel cervical myelopathy: an independent matched cohort analysis. Spine 2001;26:1330–1336.
2. Sani S, Ratliff JK, Cooper PR. A critical review of cervical laminoplasty. Neurosurg Q 2004;14:5–16.
3. Teresi LM, Lufkin RB, Reicher MA, et al. Asymptomatic degenerative disk disease and spondylosis of the cervical spine: MR imaging. Radiology 1987;164:83–88.
4. Yoon TS. Cervical myelopathy. Semin Spine Surg 2004;16:4.