22 Posterior Muscle Sparing Approaches for Decompression, Laminoplasty, and Laminectomy
Summary
Keywords: laminoplasty cervical myelopathy cervical laminectomy posterior cervical decompression neck pain
22.1 Introduction
By definition, laminoplasty of multiple levels is not a minimally invasive operation, in the usual sense of the term. It requires a relatively large incision and encompasses multiple levels. However, one can use muscle-sparing techniques to minimize the invasiveness of the procedure. Muscle sparing is a critical aspect of the successful deployment of motion sparing decompression in the cervical spine. Posterior-based motion-preserving surgery in the cervical spine includes foraminotomy, laminectomy, and laminoplasty when performed without fusion. These procedures are commonly used in conjunction with one another to achieve spinal cord and nerve root decompression, while preserving both cervical motion and segmental stability in the subaxial cervical spine.
Preservation of the intrinsic and extrinsic cervical musculature to the greatest possible degree is critical to maintaining motion, proprioception, and stability in the cervical spine. Disruption of the posterior musculature and nonanatomic reconstruction of the muscular attachments have been implicated in axial and periscapular pain postoperatively and impaired postoperative outcome scores. In our practice, meticulous dissection, preservation of muscular attachments when possible, and anatomic multilayered closure are cornerstones for successful surgical approaches. Our techniques and methods will be discussed in detail below.
During a surgical approach, the intrinsic muscles are most at risk during subperiosteal exposure of the dorsal elements. Insult to these muscles includes disruption of the muscle origin, disruption of the muscular insertion, denervation, thermal injury to muscle fibers, and nonanatomic reattachment of healing of muscles. We will describe methods to mitigate approach-related morbidity during laminoplasty of the subaxial spine with foraminotomy and laminectomy performed as indicated on a patient-specific basis. With appropriate combination of these techniques, adequate decompression of the spinal canal and neuroforamen can be achieved while preserving both segmental stability and cervical motion.
Cervical laminoplasty is well-established treatment for cervical myelopathy and myeloradiculopathy resulting from congenital stenosis, spondylotic stenosis, and ossification of the posterior longitudinal ligament (OPLL). Laminoplasty was originally performed in 12 myelopathic patients by Tsuji in 1982 where he cut the lamina bilaterally at the stenotic levels and allowed the resultant “lamina-flap” to “float” on top of the dura thus expanding the spinal canal.1 Subsequently, various laminoplasty methods have been described since his technique which have provided more reliable results, including French-door laminoplasty, dome-shaped laminoplasty, and open-door laminoplasty. Methods to stabilize the laminar hinges have also evolved to include miniplate fixation, suture–anchor stabilization, and ceramic plate stabilization among others.2,3,4
Hirabayashi et al first described the open-door laminoplasty in 1983, and since then it has become the most widely used laminoplasty.5 The technique involves cutting the lamina unilaterally while hinging the other side to expand the spinal canal thus creating more space for the spinal cord. Laminoplasty achieves direct decompression of dorsal impingement and indirect decompression of ventral compression and therefore is most powerful when performed over several segments in the subaxial cervical spine with lordotic alignment. Lordotic alignment augments the ability of the spinal cord to drift dorsally to away from compressive ventral pathology. Laminoplasty can still achieve adequate decompression for patients with neutral alignment (< 10 degree kyphosis). Suda et al found that when local cervical kyphosis was greater than 13 degree patient had inferior clinical outcome with laminoplasty.6 The use of the “K-line” and “modified K-line” can also help to predict if adequate spinal cord decompression can be achieved with laminoplasty.7,8,9 Recently, it has been shown that increased C2–C7 sagittal vertical alignment and higher T1 slope are correlated with loss of cervical lordosis after laminoplasty.10
22.2 Patient Selection: Indications, Contraindications
22.2.1 Indications
Cervical laminoplasty with posterior foraminotomy can provide effective decompression for multilevel cervical stenosis resulting from cervical spondylosis, congenital spinal stenosis, or OPLL. It is important to note that the effect of laminoplasty on axial neck pain is less predictable particularly when axial neck pain is attributed to cervical spondylosis and facet arthropathy. Patients with severe axial neck pain are not ideal candidates for laminoplasty. Nonetheless, a more recent study demonstrated that patients may have substantial improvements in total Neck Disability Index (NDI) score, as well as the NDI pain score after laminoplasty.11 Thus, laminoplasty may still be a good option in patients who desire motion preservation but have mild to moderate neck pain, as long as they have appropriate expectations regarding the goals of surgery.
Compared with laminectomy alone, laminoplasty decreases the risk of postoperative kyphosis by allowing paraspinal muscles to heal to bone and restoring soft-tissue tension.12 Laminoplasty offers several advantages over laminectomy and fusion for patients with cervical stenosis without predominant axial neck pain. Motion preservation is the most significant advantage. Laminoplasty mitigates the risk of cervical pseudoarthrosis in patients with risk factors for nonunion. In addition, it prevents soft-tissue scarring on to the dura by preserving the protective bony elements which prevents soft tissue and scar bucking into spinal and provides bony landmarks during dissection in revision surgery. Furthermore, exposure for laminoplasty is less morbid and instrumentation is less extensive compared with laminectomy and fusion, which is associated with a faster recovery.13
22.2.2 Contraindications
Cervical kyphosis in the region of planned posterior decompression is a contraindication to laminoplasty as the cord may remain draped over the kyphotic segment without lordotic alignment to allow cord drift back. However, in setting of mild kyphosis and circumferential stenosis, laminoplasty can still be a good treatment option as dorsal compression can be relieved directly. These patients must understand that if laminoplasty results in suboptimal clinical improvement from persistent ventral pathology anterior decompression and fusion to address ventral pathology or posterior fusion for realignment may subsequently be indicated.
An important concept to understand is that for myelopathic patients with kyphotic alignment and anterior compression who have adequate cerebrospinal fluid dorsally, draping of the cord over the ventral pathology must be alleviated to achieve clinical success. This phenomenon is best illustrated by the concept of the “K-line,” introduced by Fujiyosh et al. He described a straight line drawn between by connecting the midpoint of the spinal canal at C2 and C7 on standing neutral lateral cervical X-rays, to predict the position of the spinal cord after laminoplasty and correlated this measurement to clinical success in patients with OPLL.7 They found that when anterior compression crossed the “K-line” neurological recovery was worse.
Taniyama et al similarly described the modified “K-line” differing in that it was based on a sagittal magnetic resonance imaging (MRI) which allow for better assessment of ventral pathologies that were not visible on X-rays. He demonstrated that patients with < 4 mm between the modified K-line and the anterior compressive pathology had much higher risk for persistent anterior spinal cord compression after laminoplasty.8,9 In select cases, laminoplasty can be combined with an instrumented posterior fusion to address multilevel stenosis with kyphotic deformity. This has the advantages of increasing surface area for fusion and preserving the protective bony elements, though this concept has not been studied extensively.
In patients with cervical myeloradiculopathy, posterior foraminotomies can be used along with laminoplasty to relieve the nerve root compression, particularly when symptomatic root compression is unilateral. The axial imaging, MRI, and computed tomography (CT) should be studied carefully to determine if foraminotomy is likely to provide adequate root decompression on a case-by-case basis. Although bilateral foraminotomies have been performed with open-door laminoplasty, foraminotomy on the hinge side is technically demanding and may lead to a higher rate of hinge fracture.
Severe axial neck pain is a contraindication to laminoplasty. Although, interscapular and upper trapezial pain are often results of radiculopathy due to foraminal stenosis, that usually improve after posterior foraminotomies at the appropriate levels. Hosono et al reported postoperative axial neck pain prevalence to be 60% following laminoplasty as compared with 19% following anterior fusion operations.14 Contrastingly, Yoshida et al found that French-door laminoplasty had no effect on either the development or resolution of neck or shoulder pain.15 For patients with preoperative neck pain, it is imperative to discuss appropriate postoperative expectations prior to surgery. Laminoplasty may also be performed in patients with degenerative spondylolisthesis if there is no gross instability present. Shigematsu et al fount that spondylolisthesis in elderly patients was not associated with worse outcome after laminoplasty; this finding is reflected in our experience as well.16
22.3 Preoperative Planning
A thorough patient evaluation should be performed prior to surgery. A complete history and relevant physical examination should be performed. All indicated diagnostic imaging modalities should be reviewed.
The relevant history included the onset and progression of symptoms of myelopathy in the upper and lower extremities. With prompting patients may endorse weakness or numbness, reduced fine motor skills often noted with handwriting or buttoning a shirt, changes to gait or balance, falls, or changes to bowel or bladder function. Discrete radicular symptoms may be superimposed. The distribution of neck pain and arm pain or numbness should be noted.
Physical exam begins with observation of the patient’s seated and standing balance, the width, breadth, and cadence of their gait with and without assistive devices. Range of motion in the neck should be noted in addition to positions or motions that exacerbate neck or arm pain. Muscle strength should be graded from 0 to 5, and sensation should be tested with light touch and pin prick along the standard dermatome test areas. Finally, reflexes should be documented in the upper and lower extremities and pathologic reflexes should be documented if present including Hoffman’s, inverted brachioradialis, ankle clonus, and Babinski.
It is critical to understand the range of motion as well as the resting cervical alignment. Thus, plain radiographs should include anteroposterior (AP) and lateral radiographs, flexion and extension lateral radiographs, and oblique radiographs (to visualize the neural foramen) of the cervical spine. In addition to cervical alignment and range of motion, radiographs are used to assess spondylosis, instability, and spondylolisthesis, developmental stenosis, foraminal stenosis, autofusions, and other pathologies of the cervical spine. MRI is used to evaluate the cranial and caudal and extent of stenosis and the severity of central and foraminal stenosis. The etiology of stenosis at each segment should be noted including disc bulging, uncovertebral and facet arthrosis, hypertrophy and infolding of the ligamentum flavum, underlying developmental stenosis, deformity, or OPLL. CT of the cervical spine is indicated when OPLL is suspected and to further characterize osseous foraminal stenosis from uncovertebral or facet arthrosis. A topical three-dimensional (3D) reconstruction of the CT scan can be used to understand the bony surface anatomy and shape of the spinal canal. If MRI is contraindicated, CT myelography can help to evaluate the severity of canal stenosis.
We favor using bivector traction involving two ropes attached to the Gardner–Wells tongs at different vectors, one which will extend the head and neck and one which will keep the neck in gentle flexion. The procedure begins with 15 pounds applied to the Gardner–Wells tongs on the flexion rope to optimize surgical exposure and then extended using the extension rope to as necessary to assess range of motion prior to closure.
22.4 Patient Positioning
Bivector traction involves two ropes attached to the Gardner–Wells tongs at different vectors, one which will extend the head and neck and one which will keep the neck in gentle flexion. The flexion rope is aligned with the external auditory meatus and cranial vertex which will place the cervical spine in slight flexion; the extension rope is routed over an elevated crossbar at the head of the Jackson frame, and will gently extend the neck when it is bearing the weight. The procedure begins with 15 pounds weight applied to the Gardner–Wells tongs on the flexion rope to optimize surgical exposure (Fig. 22.1) and then extended using the extension rope to as necessary to assess range of motion prior to closure.
Fig. 22.1 A photograph demonstrating the bivector cervical traction setup with Gardner–Wells tongs.
Once the patient is secured to the frame with the abdomen hanging free, the bed should be put in slight to reverse Trendelenburg to reduce venous pressure at the wound, as well as facial and laryngeal edema. A forced-air warming blanket is most effective when placed beneath the patient and Jackson frame as the rising warm air will prevent ventral thermal losses and prevents the blanket from interfering with the drapes. The posterior neck is prepped and draped from the occiput proximally to the upper thoracic spine with sufficient skin exposure on either side to allow lateral passage of drains at the distal edges of the wound.
Preservation of the cervical musculature to the greatest possible degree is critical to maintaining motion, proprioception, and stability in the cervical spine. Disruption of the posterior musculature and nonanatomic reconstruction of the muscular attachments have been implicated in axial and periscapular pain postoperatively and impaired postoperative outcome scores. In our practice, meticulous dissection, preservation of muscular attachments when possible, and anatomic multilayered closure are cornerstones for successful surgical approaches.
22.5 Surgical Technique
22.5.1 Surgical Exposure
Prior to incision, surgical levels are identified using the lateral fluoroscopy. The skin is incised from C3 to C7 in the midline centered over the spinous processes (Fig. 22.2). All subcutaneous dissection are done with electrocautery. Repalpation of the spinous processes ensures that dissection remains in the exact midline where an avascular plane can be exploited. The aponeurosis of the extrinsic cervical muscles (trapezius, rhomboids, and levator scapulae) form a relatively avascular plane along the central raphe. Blood loss can be minimized by careful dissection in the midline. Metzenbaum scissors can be used to spread in line with muscle fibers to identify and develop the avascular midline raphe. Meticulous dissection and attention to the tissue planes maximize potential for wound healing and reduce the pain associated with muscle injury.
Fig. 22.2 Incision viewed through the magnification of the operative microscope. Cranial is to the image’s left side. Routine palpation and blunt finger dissection is performed to ensure that exposure occurs down the avascular midline plane. Demonstrated is dissection along the avascular midline plane during exposure to minimize blood loss when performed in this manner.
Muscle injury occurs with detachment of the origin, detachment of the insertion, denervation, or direct injury to the muscle fibers. With cervical laminoplasty using open-door technique, disruption of the intrinsic muscle insertion is inevitable; however, injury to the origin can be limited by minimizing the extent of lateral dissection and denervation and muscle fiber injury can be avoided with careful technique.
After the superficial paraspinal muscles are separated in the midline down to the level of the spinous processes, the monofid and bifid spine processes can be palpated. The spinous process can be marked with a clamp and the level of dissection verified with lateral fluoroscopy. The monofid spinous processes of C7 and at times C6, the midline of the dorsal process is exposed with electrocautery down to the level of the lamina, followed by sharp dissection using a Cobb elevator assisted by electrocautery to release tendinous attachments. The anatomy of the bifid spinous process can be utilized to enter the subperiosteal plane of dissection. Cautery is used along the midline sulcus of the bifid spinous processes dorsally, leaving muscle attachments at the dorsal tips and lateral edges of these processes (Fig. 22.3).
Fig. 22.3 Magnified view of the exposure down to the spinous process minimizing blood loss. Electrocautery is used to dissect down to the bifid spinous processes dorsally, leaving muscle attachments at the dorsal tips and lateral edges intact. A small bone cutter (marked A) is used to cut the tip of each bifid process at each level. Once the tip of the bifid process is cut, it is tagged with a nonabsorbable braided tagging suture (marked B). This is repeated at each caudal level. Shown here is one entire side with tagged bifid bone fragments. This is repeated again on the contralateral side until both sides of the wound have tagged bone fragments.
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