Laminoplasty

Background

Laminoplasty describes the process of increasing the space available for the spinal cord by reconstruction of the laminar arch via a posterior approach. Laminotomy ^[1] is the surgical removal and subsequent reinsertion of laminae and spinous processes, whereas laminectomy represents the removal of the lamina and the spinous process. The term laminotomy is often incorrectly used to describe a partial laminectomy. ^[2] A partial or hemilaminectomy is the removal of the lamina on one side, starting from the medial aspect of the facet joint to the lateral aspect of the base of the spinous process, usually without removal of the spinous process itself. For each of these procedures, a plethora of technical modifications have been proposed.

This topic describes the most commonly performed techniques of laminoplasty in the cervical and thoracolumbar spine. The definitions of Yucesoy and Sonntag ^[2] were used for this chapter, as described in the table below.

Table 1. Terminology (Open Table in a new window)

Cervical laminoplasty was developed in Japan in the 1970s to overcome challenges associated with the treatment of ossification of the posterior longitudinal ligament (OPLL) and degenerative spinal canal stenosis. ^[3] Since the anterior approach for OPLL was found to have a significant risk of complications and OPLL has a higher prevalence in Japan, Japanese neurosurgeons led the way in refining posterior approaches. ^[4] All technical variations of cervical laminoplasty (reviewed by Casey and Crockarda ^[5] ) share the aim of reconstructing the spinal canal to relieve cord compression and prevent its recurrence. ^[6]  

Laminoplasty on the thoracic and lumbar spine was first described by Raimondi and colleagues in 1976 as a technique in children for whom the high risk of instability dictated the need for replacement of the laminar arch after laminectomy. ^[7] It has been used commonly for access to the spinal cord for indications including syringomyelia, tumors, functional, and pain surgery. ^[8] 9 Degenerative and congenital lumbar stenosis is treated by laminectomy or the less invasive interlaminar fenestration with decompression. ^{[9, 10, 11, 12, 13]}

Relevant anatomy

The cervical spine is made up of 7 vertebrae. The first 2, C1 and C2, are highly specialized and are given unique names: atlas and axis, respectively. C3–C7 constitute subaxial cervical vertebrae, having a body, pedicles, laminae, spinous processes, and facet joints.

The cervical spine is more mobile than the thoracic or lumbar regions of the spine. Unlike the other parts of the spine, the cervical spine has transverse foramina in each vertebra that bear the vertebral arteries usually in segments C1–C6 ^[14] that supply blood to the brain.

The spinal cord is located inside the vertebral canal, which is formed by the foramina of 7 cervical, 12 thoracic, 5 lumbar, and 5 sacral vertebrae, which together form the spine. The spinal cord extends from the foramen magnum down to the level of the first and second lumbar vertebrae (at birth, down to second and third lumbar vertebrae).

For more information about the relevant anatomy, see Cervical Spine Anatomy and Topographic and Functional Anatomy of the Spinal Cord.

Indications

Laminoplasty is the mainstay of treatment for cervical stenosis due to OPLL.{ref3 Patients with degenerative spinal stenosis due to spondylotic myelopathy show benefit at least equal to laminectomy after spinal decompression with laminoplasty. ^{[15, 6]}  In the thoracic and lumbar spine, laminoplasty serves mainly as a surgical method to access underlying spinal disease (eg, tumor, syringomyelia). ^{[16, 17]}

A physiological spinal alignment is the prerequisite for a laminoplasty. Instability or malalignment should prompt the preoperative evaluation of the need for instrumentation. Especially helpful for when to use laminoplasty for cases with OPLL is the K-Line, a virtual line that connects the midpoints of the anteroposterior diameter of the spinal canal at C2 and C7 in a plain lateral radiogram. The K-line is positive when the peak of OPLL does not exceed the K-line and negative when the peak of OPLL exceeds the K-line. Decompression by laminoplasty should not be used if the K-line is negative,  but anterior decompression and fusion or posterior decompression with instrumented fusion are applicable. ^{[4, 18]}

The most common indications for laminoplasty are shown in the table below.

Table 2. Overview of the most common indications for laminoplasty. The K-line is positive when the peak of OPLL does not exceed the K-line, and negative when the peak of OPLL exceeds the K-line. (Open Table in a new window)

Contraindications

Contraindications include the following:

• Spinal pathologies, which are best treated by an anterior approach (ie, cervical disc disease or traumatic vertebral body fracture with canal compression)

• Cervical anterolisthesis

• Instability of the affected segment

• Kyphotic deformity

• Patients medically unfit for surgery

Note that some authors suggest that mild kyphotic deformity may be compatible with good outcome after laminoplasty for selected patients with OPLL. ^{[19, 20]}  For patients without OPLL, the risk for a progressive kyphotic deformity is postoperatively higher in case of cervical sagittal imbalance and advanced age. ^[21]

Technical considerations

Procedure planning

Surgical considerations should include the following:

• Assessment of bone quality on radiograph or computed tomography

• Documentation of preoperative spinal curvature and space available for the cord

• Assessment of degenerative changes, K-line, disc disease, facet joint disease, scoliosis, and spondylolisthesis

• Exclusion of preoperative hypermobility or segmental instability using flexion-extension radiographs

• Assessment of foraminal stenosis on preoperative imaging to evaluate the need for a complementary foraminotomy

• Assessment of severity of cervical canal compromise to establish the need for a rigid neck collar until positioning of the patient in the operating theater

Complication prevention

Care should be taken not to enter a stenotic spinal canal with the foot plate of a Kerrison punch to avoid inadvertent compression. While drilling, direct contact of the drill bit with any loose material (eg, muscle, cottonoids) should be avoided. Moreover, irrigation should be applied copiously to minimize heat transmission to surrounding tissue, which might increase the risk for C5 palsy. ^[22]

A surgical microscope should be used to improve visualization when working in proximity of the spinal canal. ^[23] Throughout the procedure, meticulous hemostasis is achieved with bipolar cautery and hemostatic material. Epidural bleeding is usually well controlled by gelatin foam.

Biomechanical considerations

In contrast to laminoplasty, laminectomy leads to a more complete removal of the medial posterior tension band structures such as the supraspinous ligament, interspinous ligament, ligamentum flavum, spinous processes, and the muscle insertions on the midline. Initially, laminectomy provides an optimal posterior decompression. Depending on the initial stability and shape of the patient’s spine, however, laminectomy is associated with a risk of postoperative instability and kyphosis. ^{[24, 25, 6, 18]}

The risk of postlaminectomy instability is highest in the cervical spine and lowest in the lumbar spine. ^[26] Because no randomized controlled trials comparing laminectomy to laminoplasty exist, the potential for postlaminectomy instability is discussed below to provide assistance in decision-making.

Cervical laminoplasty

In the cervical spine, two thirds of the axial load is distributed along the posterior elements, including the facet joints. Once a laminectomy has been performed, the facets and anterior elements take over a more prominent part in weight bearing. This favors the progression of kyphosis with an increasing stress on the remaining muscles of the posterior tension band. ^{[27, 28]}

Nonetheless, the risk of kyphotic progression after laminectomy is low in a well-aligned and lordotic spine. Advanced age and cervical sagittal imbalance are independent preoperative risk factors for postoperative kyphotic deformity following cervical laminoplasty. ^[21] In men, the normal values of cervical spinal lordosis measured from C2 to C7 range between 16 and 20 degrees; in women, they are between 15 and 25 degrees. ^[29]

The presence of degenerative disease of the cervical spine increases the risk of postoperative deformity. A Japanese series of 64 adult patients found that 36% showed a change in spinal curvature after multilevel laminectomy and 14% developed a kyphotic or meandering deformity. ^[30] Moreover, the removal of more than 25% of the medial facet joints during cervical laminectomy increases the risk of instability and progressive deformity. ^{[31, 32]} After laminoplasty, the change in sagittal Cobb angle is less than two degrees over a median follow-up of almost three years. ^[33] Moreover, postoperative improvement rates in neurological status appears to be comparable after laminoplasty or laminectomy with fusion. ^{[34, 35, 36, 21]}

Thoracic laminoplasty

Compared with the cervical spine where the posterior elements are exposed to most of the loading stress, the load axis of the thoracic and lumbar spine shifts anteriorly. As a consequence, procedures performed on the posterior elements in the lumbar spine may have a less immediate and dramatic effect on the spinal curvature.

The incidence of postlaminectomy deformity in the thoracic spine is low, as long as more than 50% of the facet joints are left intact. Aizawa et al found progression to kyphosis of 2.5 degrees per level in women and 0.6 degrees in men after a minimum of two years' followup after thoracic multilevel laminectomy.

Kyphosis is more likely to occur after laminectomy in the lower thoracic spine, which is explained by the lack of direct contact of the five lower ribs with the sternum. ^[37]

Lumbar laminoplasty

After lumbar laminectomy, rates between 0% and 6% of postoperative instability were reported. The rate of instability increases to 15% when laminectomies are performed on 3 or more levels. ^[38] Some authors advocate fusion for more than 3-degree motion on flexion-extension x-ray or for laminectomies spanning 3 or more levels. ^[39]

Children

The risk of instability is highest in the immature spine of a child, where postlaminectomy deformity uniformly affects over one third of patients. ^[40] The predisposition of children to develop spinal instability after laminotomies is multifactorial and is in part ascribed to higher content of cartilage, a more horizontal alignment of facet joints, more flexible ligaments, growth of the spine, and the disease process itself. This risk of kyphosis can be decreased significantly when laminoplasty is performed instead of laminectomy. ^{[41, 42]} One study found no difference in complications after tethered cord release using laminotomy or laminoplasty. ^[13] However, the need for fusion may be unavoidable if postoperative deformity occurs. ^[43]

Patient education and consent

Patients may perform activities of daily life but should refrain from major physical activities until 6 weeks after surgery. They should be counseled on an individual basis regarding their ability to return to their previous occupation or physical activities. Patients are instructed to see a healthcare specialist if preoperative symptoms recur or new symptoms develop.

Equipment

The authors use fluoroscopy to verify that the incision is placed above the targeted segments. Once the spinous processes have been exposed and retractors are in place, another intraoperative fluoroscopy shot is obtained to document exposure at the intended levels.

In case of cervical laminoplasty procedure, intraoperative electrophysiological neuromonitoring did not significantly impact outcomes. ^[44] Electrophysiological monitoring is advocated for cases in which intradural surgery is performed. Moreover, in cases of severe cord or root compression, preoperative and intraoperative evaluation of motor and sensory evoked potentials is helpful. ^[45]

Other instruments include the following:

• Standard spine surgery equipment ^[46]

• Monopolar and bipolar cautery

• Kerrison punches (1-mm to 4-mm sizes)

• Angled cerebellar retractors

• High-speed footplate drill (craniotome)

• Diamond and rose burrs (2-mm and 3-mm sizes)

• Gelatin foam and bone wax for hemostasis

• Titanium miniplates and 4- to 6-mm screws

Patient preparation

Anesthesia

In case of compression-induced myelopathy or cervical spinal instability, the surgeon should discuss the need of awake-fiberoptic intubation to prevent neurological injury due to hyperextension of the neck.

Muscle relaxation and anesthetics need to be compatible with electrophysiological neuromonitoring. The specific monitoring needs are discussed ahead of surgery anesthesiologists and electrophysiologists. Neuromuscular blockade should be discontinued once intubation and positioning are completed. Somatosensory-evoked potentials and motor-evoked potentials are affected by inhaled anesthetics, and intravenous agents are generally preferred. ^[45]

Analgesia is identical to other types of spinal surgery.

Positioning

Sufficient room for chest expansion should be secured; appropriate padding is required.

Abdominal compression in the ventral position should be avoided, using adequate cushions to improve venous return and allow for bloodless surgery. In cases with severe spinal cord compression or if spinal cord injury with ischemia is suspected preoperatively or perioperatively, blood pressure should be maintained within 10-20% of preoperative values.

For cervical laminoplasty, the patient is placed in a prone position, and the chest is padded and the head is fixed using a Mayfield headholder in slight forward flexion (“military chin tuck”). ^[47] Sufficient space is left between the chin and the chest to allow for adequate venous return. Some surgeons have suggested releasing this slight forward flexion during surgery once decompression is achieved to adapt osteosynthesis to the cervical lordosis.

For thoracolumbar laminoplasty, the patient is placed in a prone position. For lumbar procedures, the arms can be placed parallel to the torso pointing cephalad to allow the surgeon comfortable access to the situs. For thoracic laminoplasty, the arms are placed lateral to the torso and point caudally. The anesthesiologist should be allowed comfortable handling of the venous lines, oxygen saturation, and blood pressure instruments. Appropriate padding is provided to chest and abdomen to avoid compression.

Monitoring and follow-up

Unless neurological deficits exist, patients are asked to walk on postoperative day 1 and adequate physiotherapy is prescribed to improve neuromuscular function. Particularly in the cervical spine, operated segments should be allowed time to heal. Therefore, in children and adults, the authors recommend a 6-week immobilization using a rigid collar or brace for less axial neck pain and to allow for healing of the repositioned bone material. However, a postoperative rigid cervical collar has no impact on complications or quality of life. ^{[48, 49]}  Adults therefore may not formally require a brace or collar, but may be offered a soft collar for 1–4 weeks. Wound care and analgesics are administered according to standard protocols.

Patients undergo imaging as required for their main diagnosis (eg, follow-up magnetic resonance imaging for tumor or plain radiograph for fusion success after laminoplasty). ^[39] The authors recommend performing anteroposterior and lateral radiographs of the cervical spine after 6 weeks. The goal is to assess whether the cervical curvature has changed after surgery. Also, lateral radiographs provide information on the space available for the cord. Computed tomography with high-resolution or three-dimensional reconstruction is most helpful in the identification of osseous compression, deformity, bone quality, and construct failure.

Moreover, restenosis is a potential late complication due to bony compression, which needs to be excluded by imaging in case of symptom recurrence.

Complications

Range of motion

Although the reinsertion of posterior elements is performed with the aim of preserving the continuity of the bony spine, laminoplasty alters biomechanics. Although it allows for more flexibility than a fusion procedure, the range of motion of the cervical spine may decrease progressively after laminoplasty. ^{[50, 51]} Patients may even experience spontaneous fusion of the operated segments. ^[52]

Kyphosis

Progression to kyphosis of a previously well-aligned spine occurs after laminoplasty for tumors in about 9% of patients in an overall analysis. ^[53] The rate of kyphosis for patients undergoing cervical laminoplasty is higher and can reach 15%, while worsening of the cervical curvature can be observed in over one fifth of patients. ^[50]  After a unilateral approach for cervical laminoplasty no kyphotic deformity was observed 6 months after surgery. ^[28]

Postoperative pain

Axial neck pain is a common postoperative complication of cervical laminoplasty.  ^{[54, 55]} Temporary axial neck pain occurs in up to 60% that decreases significantly within 6 weeks and one year postoperatively. ^[56] Shoulder pain also occurs commonly, often ipsilateral to the hinged side. ^[57] If the usual pain medication including anti-inflammatory drugs and opiate drugs fail to alleviate the pain, imaging is indicated to exclude spinal instability, postoperative hematoma, and cord or nerve compression due to bony spurs or osteosynthetic material.

Radiculopathy

As in every procedure that involves bonework in or around the spinal canal, there is a small risk of injury to nervous tissue. C5 palsy is the most prevalent complication after laminectomy, owing to the relatively short length of the C5 root and its anterior position on the cord, which may be subject to stretching once posterior decompression is achieved. Reports on C5 palsy after laminoplasty range from about 2% for severe deltoid muscle palsy ^[58] to 8% for temporary but clinically evident radiculopathy, which may last for several months. ^[50] This can be due to inadvertent mechanical compression or to the heat transmitted by a high-speed drill. ^[59]  Another study revealed that the space anterior to the spinal cord was associated with postoperative C5 palsy after expansive open-door laminoplasty. ^[60]  Furthermore, acute deltoid weakness after cervical laminoplasty could be predicted with intraoperative neuromonitoring and 100% sensibility and specificity. However, intraoperative neuromonitoring was not able to detect delayed-onset deltoid weakness. ^[59]

Some authors suggest that preoperative assessment of the presence of foraminal stenosis should prompt foraminotomy for neural decompression on the affected segment and prevent mechanical stress on the affected nerve root after decompression. ^{[51, 61]}

Material dislocation

Segmental palsy due to dislodged laminae was found in 1.4% of cervical laminoplasties in a long-term follow-up study. ^[19]

Cord compression/hematoma

Intraoperative lateral fluoroscopy, solid osteosynthesis, flattening of the ventral surface of the laminae and, finally, fascial closure with deep sutures involving the spinous processes are necessary to prevent “sinking” of the laminotomy flap, which may cause a mass effect. Postoperative deficits should always prompt urgent imaging to exclude postoperative cord or nerve root compression due to bone or an epidural hematoma.

Cervical laminoplasty

After fluoroscopic verification, the skin incision is performed in the midline, about 2 cm above the most cephalad down to the level of the most caudal exposed spinous process and continued sharply through the subcutaneous fat. Midline orientation is kept by palpation of the spinous processes and identification of the white nuchal ligament. The nuchal ligament is incised strictly in the midline using monopolar cautery to preserve its muscle insertions (from superficial to deep: trapezius [upper fibers], rhombdoid minor, splenius capitis, and serratus posterior superior).

Once the spinous processes are exposed, the supraspinous ligament is left intact and a subperiostal dissection is performed down to the laminae bilaterally using monopolar cautery and raspatory. The spinalis portion of the erector spinae, semispinalis, multifidus, and rotator muscles are thus lateralized. The need to involve C2 or C3 in a laminoplasty should be weighed against the increased potential for instability. If necessary, a partial or complete laminectomy of the most cranial segment can be performed, working from distal to proximal underneath the vertebral attachments to minimize disruption. ^[62]  In some cases with cervical spondylotic myelopathy, a segmental partial laminectomy or hemilaminectomy is sufficient to achieve minimum posterior decompression with less postoperative neck pain when compared with C3–C7 laminoplasty. ^{[63, 64]}

Care is taken to stay on the lateral aspect of the spinous process and perform dissection only along a corridor of bony resistance. Any force applied to the laminae is directed laterally and not downwards to prevent impaction into the spinal canal due to fragile bone or spina bifida. Cottonoids are applied for more gentle muscle handling and can be temporarily left in place on one side for hemostasis during contralateral dissection.

Dissection should be sufficiently lateral to visualize the medial half of the facet joints (see the image below) while avoiding penetration of the facet capsule.

Cervical laminoplasty is presented on a sawbone model of the cervical spine. A: Levels C3 to C7 are exposed. B: For a C4-6 laminoplasty, the inferior aspect of the lamina of C6 is undermined using a Kerrison punch to create an entry for the craniotome (arrow). C: A temporary longitudinal miniplate (arrow) is applied as medially as possible on the laminae to preserve the physiological alignment. D: Once the troughs are cut, the laminar flap can be removed. E: This figure demonstrates a left open door laminoplasty, the spinal canal is opened only on one side. Some authors suggest to place a bone wedge (eg, rib or spinous process, represented by the red rectangle) between the opened laminar arch and the lateral mass (arrow) in order to maintain curve of the laminar arch. F: Final result of a bilateral miniplate laminoplasty. The miniplates are attached to the center of the dorsal surface of each respective lateral mass. Prior to reinsertion of the flap, osteotomy of the ventral aspect of the laminae is performed (not shown) to maximize the space available for the cord.

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Visualization of the facet joint can be obtained by carefully shifting two adjacent spinous processes against one another. This maneuver produces bulging folds in the capsule of the facet joint, which represent a useful landmark.

Spinal retractors (or cerebellar angled retractors) are then placed and fluoroscopy is used for verification.

The inferior border of the lowest lamina is identified using a Penfield no. 1 dissector. Careful undermining should expose its inferior aspect. Medial to the facet joint and lateral to the insertion of the spinous process, a few millimeters of bone are removed on each side with a Kerrison punch to create an entry point for the footplate of the drill (see the image above).

The laminar arches can be temporarily connected using osteosynthetic plates (see the image above). ^[65] This temporary maneuver prevents shrinking of the construct and facilitates its reimplantation after laminotomy. The plates can be removed after reinsertion (see the image above).

The ligamentum flavum is left in place for protection until the bone work is done. A craniotome or drill is then used to draw through along a line just medial to the facet joints and parallel to the spinous processes.

It is not unusual to find insurmountable resistance when initiating the bone cut using a craniotome. If angulation of the craniotome laterally and posteriorly does not lead to a cut in the desired direction, one should not apply force but rather abandon this technique. Instead, a rose burr (2 mm or 3 mm) should be used to drill a trough into the lamina just medially to the facet joint (see the image above).

Once the inner cortical layer is reached, a diamond bur is used to progressively thin out the laminae. Irrigation is applied copiously to reduce heat transduction to nervous tissue. The trough can be completed with a Kerrison punch.

Next, four variations of laminoplasty are described: Z-laminoplasty, hinged-door laminoplasty, midline-enlargement laminoplasty, and the bilateral miniplate laminoplasty.

Z-Laminoplasty

In Z-laminoplasty, the spinous processes are removed and the laminae thinned using a diamond burr. The laminae are split in a transverse direction and reapproximated in an augmented fashion using nonresorbable sutures (see the image below).

Four different types of laminoplasty are depicted schematically. A: The Z-laminoplasty was the first laminoplasty technique, developed by Hattori in 1972. Using a posterior midline approach, the spinous process is removed while leaving the lamina mostly intact. The laminar arch is split in the horizontal plane to produce one flap on each side. The flaps are hinged open and fixed. While this is a technically difficult method, it has led the way for the development of several other techniques. B: In the hinged-door laminoplasty, only one side of the laminotomy troughs is opened and the laminae are hinged to one side. The hinge is left on the side where one anticipates the lesser need for decompression, i.e. contralateral to the main symptoms in case of lateralization or contralateral to a potential foraminotomy. Holes are drilled through the lateral mass of the hinge-side and a non-resorbable suture maintains lateral retraction of the hinged laminae. An interposition graft (rib, spinous process) can be used as a spacer and can be wedged between the medial part of the lateral mass and the laminae. C: In the midline-enlargement laminoplasty, both lateral troughs are drilled without penetrating the inner cortical layer of the laminae. The principle is to use the lateral troughs as hinges and split the lamina along the midline. The spinous processes can be divided with a drill or saw. Once the spinous process is split, the hemi-arches are reflected laterally to each side. A ceramic, hydroxyapatite or bone graft is wedged into place and secured into place to keep both laminar wings apart. D: The bilateral miniplate laminoplasty is based on a bilateral opening of the laminar trough. The arches are removed for reconstruction with osteosynthetic miniplates. The laminotomy block can be removed to allow access the spinal canal for further decompression. After trimming the anterior border of the laminar arch (shaded area), the flap is secured to the lateral masses using miniplates. The cephalad and caudal ends of the flap are sutured to the supraspinous ligaments.

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This procedure is technically demanding and is not practiced widely, but has paved the way for several other methods of cervical laminoplasty. ^{[66, 67]}

Hinged-door laminoplasty

It is possible to open only one of the laminotomy troughs and to hinge the laminae open to one side (see the image above). The hinge is left on the side, where one anticipates the lesser need for decompression (ie, contralateral to the main symptoms in case of lateralization or contralateral to a potential foraminotomy).

Holes are drilled through the lateral mass of the hinge side, and a nonresorbable suture maintains lateral traction on the hinged laminae. An interposition graft (rib, spinous process) can be used as a spacer and can be wedged between the medial part of the lateral mass and the laminae. ^{[68, 69]}

Midline-enlargement laminoplasty

In the midline-enlargement laminoplasty, both lateral troughs are drilled without penetrating the inner cortical layer of the laminae. The principle is to use the lateral troughs as hinges and split the lamina along the midline. ^[70] The spinous processes can be divided with a drill. A dissector is placed under the lamina in a caudate to cephalad direction for protection during drilling.

Once the spinous process is split, the hemi-arches are reflected laterally to each side. A ceramic, hydroxyapatite, or bone graft is wedged into place and secured into place to keep both laminar wings apart (see the image above). ^[71]

Bilateral miniplate laminoplasty

In this technique, the laminae are opened on both sides and the arches are removed for reconstruction with osteosynthetic miniplates (see the image below).

Cervical laminoplasty is presented on a sawbone model of the cervical spine. A: Levels C3 to C7 are exposed. B: For a C4-6 laminoplasty, the inferior aspect of the lamina of C6 is undermined using a Kerrison punch to create an entry for the craniotome (arrow). C: A temporary longitudinal miniplate (arrow) is applied as medially as possible on the laminae to preserve the physiological alignment. D: Once the troughs are cut, the laminar flap can be removed. E: This figure demonstrates a left open door laminoplasty, the spinal canal is opened only on one side. Some authors suggest to place a bone wedge (eg, rib or spinous process, represented by the red rectangle) between the opened laminar arch and the lateral mass (arrow) in order to maintain curve of the laminar arch. F: Final result of a bilateral miniplate laminoplasty. The miniplates are attached to the center of the dorsal surface of each respective lateral mass. Prior to reinsertion of the flap, osteotomy of the ventral aspect of the laminae is performed (not shown) to maximize the space available for the cord.

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Both laminotomy troughs are cut through. Then, the interspinous ligament of the most caudal vertebra is divided using scissors or a scalpel. The assistant lifts the spinous process of the lowest vertebra under slight tension to allow the surgeon to perform a dissection of the ligamentum flavum, bridging vessels and dural adhesions while the laminar arches are progressively lifted en bloc.

Depending on the type of procedure, the most cranial interspinous ligament can remain attached in situ. The laminotomy block can be reflected upward when both troughs are cut or reflected laterally when a hinge is performed. In cases in which temporary access to the spinal canal is needed (eg, in tumor surgery), the laminar arches may be buried between the spinal retractor and the laterally displaced paraspinal muscles until the intraspinal part of the surgery is completed.

Gentle inspection of the bony borders of the spinal canal is performed to identify points of compression on the cord. A diamond high-speed drill or a 2-mm Kerrison punch are used to remove any protrusions. Spondylotic facets can be undermined. At this stage, performing a posterior foraminotomy in addition to laminoplasty is possible if preoperative imaging or clinical findings suggest nerve root impingement. ^[51] For technical details on posterior foraminotony, see the article by Jagannathan and Sherman. ^[72]

The laminar flap is prepared using titanium miniplates, which reach sufficiently lateral to be attached to the lateral masses. ^{[73, 74, 75]} The anterior aspect of the laminae is thinned as much as possible to increase the space available for the cord and avoid restenosis. Once the laminae are reinserted and screwed into place (see the image above), the stability of the construct is tested by manual manipulation. A dissector is used to check that the space underneath the reimplanted laminae is not in direct contact with underlying structures. The temporary longitudinal miniplate is removed. A 1-0 non-resorbable braided suture can be used to attach the supraspinous ligaments on the caudal and cephalad ends of the flap to the adjacent spinous processes.

Closure is performed on the fascia including the nuchal ligament using resorbable 1-0 sutures and the subcutaneous and cutaneous closure is performed as usual.

Thoracolumbar laminotomy

An incision is placed in the midline, starting about 3 cm above the most cephalad spinous process down to the level of the most caudal spinous process and continued sharply through the subcutaneous fat. The thoracolumbar fascia is incised in the midline over the spinous processes and a meticulous subperiostal dissection is performed down to the laminae using monopolar cautery and raspatory.

Any force applied on the laminae is directed laterally and not downwards to prevent impaction into the spinal canal due to fragile bone or spina bifida. Cottonoids are applied for more gentle muscle handling and can be left in place on one side for hemostasis during contralateral dissection.

Dissection should be sufficiently laterally to visualize the medial half of the facet joints while avoiding penetration of the facet capsule. In the thoracic spine, visualization of the costotransverse process indicates the position of a pedicle.

Self-retaining spinal retractors are then placed and a fluoroscopy image is obtained for verification of the correct level. The inferior border of the caudal lamina is identified using a Penfield no. 1 dissector. Careful undermining should expose its inferior aspect.

Medial to the facet joint and lateral to the insertion of the spinous process, a few millimeters of bone are removed on each side with a Kerrison punch or shaved with a diamond drill to create an entry point for the footplate of the craniotome (see the image below).

An L2-4 laminoplasty is shown on a lumbar spine model. A: First, the entry point for the footplate of the craniotome is identified on the lower aspect of the lamina of L4 (arrow) and may be widened using a Kerrison punch. B: A laminotomy is performed along the trough (dotted line) with a craniotome. Slight lateral and posterior angulation may be necessary to achieve continuous drilling. C: Prior to removal of the laminae, a longitudinal miniplate may be applied to preserve the alignment of the posterior elements. Once the laminar flap is removed, the spinal canal is widened using a drill (D) and a Kerrison punch (E) until satisfactory exposure is achieved (F). G: The laminar flap is first meticulously freed of ventral adherences and ventral osteotomy of the laminae is performed to minimize the risk of canal stenosis. Miniplates secure the flap laterally to the pars interarticularis.

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The ligamentum flavum is left in place for protection until the bone work is done. A craniotome or drill is then used to cut along a line parallel to the spinous processes (see the image below).

Depiction of a case of thoracolumbar laminoplasty for a Th12-L1 ependymoma of the conus medullaris. A: Sagittal contrast enhanced T1-weighted MRI shows a space-occupying intradural lesion of the thoracolumbar junction. B: Following exposure of the laminae of Th12 and L1, a longitudinal trough (thin arrows) is drilled with a craniotome and the caudal and cephalad supraspinous and interspinous ligaments are bisected (thick arrows). C: The assistant progressively lifts up the laminar flap while it gently is freed from anterior adherences. D: Spinal canal exposure can be optimized as needed for tumor removal E: After removal of the tumor and watertight dural closure, the laminar flap is osteotomized anteriorly (not shown) in order to prevent iatrogenic spinal canal stenosis. Miniplates are applied laterally (arrows). The severed supraspinous ligaments are secured to the adjacent levels with braided 1-0 sutures (not shown).

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Often it is difficult to initiate the bone cut using a craniotome. If angulation of the craniotome laterally and posteriorly does not lead to a cut in the desired direction, one should not apply force but rather abandon this technique. Instead, a rose burr (3 mm) should be used to drill a trough into the lamina medially to the facet joint.

Osteosynthetic plates can be used to link the spinous processes using titanium mesh plates prior to laminotomy to preserve the length and angulation of the spinous processes. The plates are removed once the removed laminae have been fixed back into place. The ligamentum interspinosum of the most caudal vertebra is divided sharply. The assistant holds up the spinous process of the lowest vertebra under slight tension to allow the surgeon to perform a dissection of the ligamentum flavum and dural adherences.

During this procedure, the most cranial interspinous ligament can remain attached in situ. The package of spinous processes can be removed, reflected upwards, or buried between the spinal retractor and the laterally displaced paraspinal muscles until the intraspinal part of the surgery is completed.

The spinal canal is inspected for bony protrusions and residual ligamentum flavum, which are removed with a drill or Kerrison punch until satisfactory exposure is achieved. See the images below.

An L2-4 laminoplasty is shown on a lumbar spine model. A: First, the entry point for the footplate of the craniotome is identified on the lower aspect of the lamina of L4 (arrow) and may be widened using a Kerrison punch. B: A laminotomy is performed along the trough (dotted line) with a craniotome. Slight lateral and posterior angulation may be necessary to achieve continuous drilling. C: Prior to removal of the laminae, a longitudinal miniplate may be applied to preserve the alignment of the posterior elements. Once the laminar flap is removed, the spinal canal is widened using a drill (D) and a Kerrison punch (E) until satisfactory exposure is achieved (F). G: The laminar flap is first meticulously freed of ventral adherences and ventral osteotomy of the laminae is performed to minimize the risk of canal stenosis. Miniplates secure the flap laterally to the pars interarticularis.

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Depiction of a case of thoracolumbar laminoplasty for a Th12-L1 ependymoma of the conus medullaris. A: Sagittal contrast enhanced T1-weighted MRI shows a space-occupying intradural lesion of the thoracolumbar junction. B: Following exposure of the laminae of Th12 and L1, a longitudinal trough (thin arrows) is drilled with a craniotome and the caudal and cephalad supraspinous and interspinous ligaments are bisected (thick arrows). C: The assistant progressively lifts up the laminar flap while it gently is freed from anterior adherences. D: Spinal canal exposure can be optimized as needed for tumor removal E: After removal of the tumor and watertight dural closure, the laminar flap is osteotomized anteriorly (not shown) in order to prevent iatrogenic spinal canal stenosis. Miniplates are applied laterally (arrows). The severed supraspinous ligaments are secured to the adjacent levels with braided 1-0 sutures (not shown).

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Performing a thorough thinning of the laminar flap in order to prevent an iatrogenic stenosis of the spinal canal is mandatory. The construct can be reinserted and attached to the pars interarticularis on each side using titanium miniplates as described above.

The supraspinous ligaments of the uppermost and lowermost laminae are sutured to the spinous processes of the adjacent segments using non-resorbable 1-0 braided sutures. The thoracolumbar fascia is sutured tightly to the spinous processes of the laminar flap. This additional measure prevents a sinking of the flap.

In pathologies that may require repeat surgery such as tumors, some authors suggest the use of colored and nonresorbable sutures to facilitate a midline access through scar tissue. Subcutaneous and skin closures are performed as usual.