Cervical Spondylosis with Myeloradiculopathy Multilevel Laminectomy, Foraminotomy, Fusion, and Lateral Mass Plating - Post Operative Evaluation

POSTOPERATIVE EVALUATION

Immediate postoperative evaluation indicated the patient's wrist and finger extension, grip and wrist flexion to be 5/5 strength and 5/5 triceps strength in the right upper extremity. CT scans were later performed and revealed that no part of the instrumentation impinged upon the neural foramen and that there was no concern for mechanical radiculopathy (Fig 4: A, B, C). Postoperative plain radiographs indicated multiple laminectomies and posterior compression plates were anchored by threaded bone screws at C3–C6. The lower two screws on the right were slightly separated from the underlying bone and the plate. The cervical lordosis was well maintained.

At 12 months follow–up, the patient was improving but had residual neck pain and mild numbness and tingling sensations radiating down the right hand and right leg. On physical examination, she had some tightness and tenderness to palpation in the paraspinal and trapezius muscles bilaterally in the neck. Neck flexion was noted at 20 degrees, extension at 25 degrees and bilateral rotation at 35 degrees. Neurologic examination was intact although she had decreased sensation in the C5–C6 distribution on the right. Hoffman's sign was negative. Plain radiographs indicated good healing of the posterior fusion with good alignment of the cervical spine. Positioning of the lateral mass plates and screws remained unchanged. Patient's residual symptoms seemed to be consistent with arthritic and muscular pain. The patient was instructed to further continue her exercise regime and anti–inflammatory medication.

DISCUSSION

The spinal canal has a diameter of 17 to 18 mm between C3–C7 with stenosis defined as less than 13mm. 6,8,9,16,28,48 The diameter of the spinal cord is 8.5–11.5 mm occupying ½ the spinal canal at C1–C3 and ¾ at C5–C7 receiving 65–70 % of its vascular supply from the anterior spinal artery and its segmental medullary feeders. 52 Although the spinal canal could accommodate many structures, compressing elements could produce neuroischemic and mechanical nerve conduction alterations of the spinal cord and nerve roots. Such elements that threaten spinal cord and nerve root compression producing CSMR symptoms are a posterior protruding disc, OPLL, vertebral osteophytes, facet joint spurs, overriding joint of Luscka, invagination or ossification of the ligamentum flavum, foraminal osteophytes, and hypertrophy of the posterior arch.

The purpose of surgical intervention is to decompress the spinal cord and nerve roots, establish stability, and maintain alignment. Anterior decompression by anterior cervical discectomy with fusion (ACDF) is performed when three or fewer levels are involved. ACDF increases the canal size at a particular stenotic area. Bone graft may unbuckle the ligamentum flavum, provide stability of preoperative spondylolisthesis, and maintain alignment. However, ACDF may not adequately remove osteophytes or OPLL causing cord and nerve root compression, increase the risk of pseudoarthrosis with multilevel fusion, and may cause kyphosis. ACDF with corpectomy is performed when three levels or less are involved primarily to address severe preoperative kyphotic deformity providing direct anterior cord decompression and adequate removal of osteophytes and disc bulges.

When radiculopathic symptoms exist in a nonkyphotic spine with three or more level involvement and no significant neck pain, posterior decompression via laminoplasty is the surgical approach of choice. 33 However, according to Hosono et al, 75 % of the patients who underwent laminoplasty reported no preoperative neck pain, but postoperatively 60 % complained of neck pain. 37 Subsequently, to eliminate preexisting neck pain with laminoplasty may prove detrimental. Prekyphotic alignment does not improve the outcome of laminoplasty because of the lack of dorsal cord migration postoperatively and the continued exposure to anterior compression. 27,40–42,50 Therefore, if multilevel involvement is greater than three levels with preoperative neck pain and nonkyphotic deformity, laminectomy, fusion, and bilateral foraminotomy is persued. If some loss of lordosis is present, lateral mass plating is also utilized and manipulated to achieve preferred lordotic alignment and prevent postlaminectomy kyphosis and subluxation.Lateral mass plating facilitates laminectomy decompression, provides stability, prevents postlaminectomy kyphosis, promotes bone fusion, and decreases the risk of subluxation. However, if a kyphotic deformity is preexisting than lateral mass plating may not prove advantages. Furthermore, management of osteoporotic cervical spondylotic patients with posterior fusion is complex. Osteoporotic individuals possess poor bone stock that fails to adequately incorporate the screw construct to bone and could pose a threat of fracture or screw pull–out.

Although various methods of instrument application exist, proper screw trajectory and placement of lateral mass plates is essential to avoid neural and vascular damage and establish proper fixation. Two widely used screw placement methods, the Roy–Camille and Magerl techniques, have been found relatively safe with no threat to the spinal cord and vertebral arteries. 30 The Roy–Camille screw placement technique for posterior lateral mass plating dictates that a screw is angulated 10 degrees laterally from the center of the lateral mass and perpendicular to the posterior vertebral cortex. 56 Alternatively, the Magerl technique requires screw placement 2–3 mm medially and superiorly from the intersection of the lateral mass at 25 degrees lateral and 40–60 degrees superiorly to parallel the facet joint's articular surface. 45

In 1991, Heller at al compared the Roy–Camille and Magerl techniques and found no threat to the spinal cord and vertebral arteries. 30 However, the study stressed the importance of anatomical and technical knowledge to obtain beneficial results. Although no injury occurred to the spinal cord nor the vertebral arteries, Roy–Camille and Magerl techniques posed a 10.8% and 26.8% risk for nerve root injury respectively. Moreover, the Magerl screw technique presented less facet violations, but screw trajectory was difficult to assess because of drill interference by the prominent spinous process of the cervicothoracic junction.

As a response to such potential nerve root injury, An et al reported in 1991 an alternative screw placement method. 1 An et al stated that nerve root injury may decrease with more lateral and more cephalad drill trajectory. According to An et al, screw insertion is accomplished at 1 mm medially from the lateral mass center at 30 degrees laterally and 15 degrees superiorly with screw tip direction between the transverse process and facet. An et al noted that the C7–T2 region requires more lateral drilling because of the transitional vertebrae and prominent spinous processes in order to avoid the facet and obtain optimal bone purchase. Nevertheless, C7–T2 screw placement may result in decreased screw length due to increased lateral drilling. In addition, An et al remarked that vertebral variations exist between individuals and that interfacet distances are not constant. Therefore, An et al recommended oblong plate holes rather than a circular design to provide flexibility for various anatomical morphologies.

Grubb et al addressed the need of a more flexible lateral mass device to provide variability in positioning the screws in a desired position. 25 The traditional lateral mass plate and screw design was compared to a variation of the ISOLA system by fixating lateral mass screws to rods and positioning them in 12 cadavers by an An screw placement technique. Findings suggested that no difference existed between rods and plates in nondestructive torsional and lateral bending, but rod construct exhibited greater stability in destructive and nondestructive flexure. Furthermore, Horgan et al recently endeavored in a similar novel lateral mass screw–rod technique. 36 Nevertheless, such instrumentation requires further evaluation.

Although use of lateral mass plating has been widely reported, few have elaborated on its associated complications. Studies suggest that lateral mass plating could cause nerve injury, 22,31,43,70 facet penetration, 2,31 screw loosening, 2,17,30,63 screw avulsion, 17,31 screw breakage, 31 plate breakage, 31 adjacent segment degeneration, 23,31 fusion extension, 2 lost reduction, 17,31,43,58 pseudoarthrosis, 17,23,31 and infection. 2,17,31,43 Further complication could result in iatrogenic foraminal stenosis. According to Heller et al, iatrogenic foraminal stenosis results from a lag effect when the lateral mass shifts dorsally and narrows the neural foramina as a result of screw tightening to reduce gap distance between plate and bone.31 As a result, radicular symptoms develop because of nerve compromise.

CONCLUSION

Multilevel laminectomy, foraminotomy, fusion, and lateral mass plating are beneficial routes in treating myelopathy and radicular symptoms as a result of cervical spondylosis. As was evident in the report by Heller et al in 1991, 30 surgical method and outcome improves with familiarity of the technique and understanding of anatomical variations. Therefore, anatomical awareness and technical expertise are essential in obtaining optimal results and decreasing risk of complications. 1,30