Anterior reconstruction and stabilization techniques for cervical spinal metastases
VOLUME 25 • NUMBER 5 March 15, 2003
Learning Objectives: After reading this article, the participant should be able to:
1. Describe the goals and indications for surgical intervention for cervical spinal metastases.
2. Recall why anterior approaches are more effective than laminectomy for surgical treatment of spinal metastasis.
3. Describe the various techniques available for anterior reconstruction of the cervical spine after tumor resection.
Metastatic spinal tumors are the most common type of malignant lesions of the spine. The vertebral column is the most common site of bony metastasis. Between 5% and 10% of patients with systemic cancer develop spinal metastases. The cervical spine is the least involved by spinal metastases (10%), followed by the lumbar spine (20%), and the thoracic spine (70%). Breast, lung, prostate, and renal carcinomas are the tumors that most commonly metastasize to the spine. Myeloma, lymphoma, and gastrointestinal carcinoma also can invade the vertebral column. The most common symptom is neck pain (90%); more than 50% of patients can present with severe deficits, however, including acute weakness that evolves quickly to quadriplegia. Mechanical pain secondary to instability can be severe enough that basic activities such as walking can become nearly impossible. Significant bone destruction can progress to fracture, instability, deformity, and neurologic compromise. Failure of a vertebral body to support a segment of the spinal column requires effective reconstruction.
Because most metastatic lesions originate in the vertebral body, an anterior cervical corpectomy offers the most direct
The authors have disclosed that they have no significant relationships with or financial interests in any commercial organizations pertaining to this educational activity.
approach for decompression and effective reconstruction of the weight-bearing vertebral column. This approach is especially appropriate in patients with significant vertebral body destruction resulting in neck pain or symptomatic spinal cord compression. When choosing spinal reconstructive materials and techniques, multiple biomechanical factors must be considered to achieve anatomic restoration of sagittal and coronal plane deformity and physiologic load-bearing. Stabilization and reconstruction of the cervical spine after corpectomy can be performed in several different ways, and each technique has its own advantages and disadvantages. Generally, the vertebral body defect is reconstructed with bone autograft or allograft, polymethylmethacrylate (PMMA), titanium interbody spacers and cages, or a combination of these materials. Stabilization is then achieved with anterior instrumentation, usually anterior cervical plate fixation, to prevent distraction failure. Additionally, posterior instrumentation, with or without bone grafting, may be necessary to supplement the anterior construct. This lesson discusses the various techniques of anterior vertebral body reconstruction after corpectomy for metastatic tumors of the subaxial cervical spine.
Surgical intervention should be considered in each case of spinal metastasis. Indications for surgery include
Category: Cervical spine reconstruction, Spinal metastatic tumor, Corpectomy, Stabilization
Key Words: Neoplasm, Spine, Surgical technique
intractable pain, spinal cord compression, and the need for stabilization of impending pathological fractures. The primary goals of surgical reconstruction and stabilization are not cure, but, rather, palliation of pain, preservation of neurologic function, and restoration of stability to allow early ambulation and mobilization without external orthosis. These considerations are important for patients who desire comfort and ambulation during their remaining life expectancy. Consideration for surgical treatment of these patients must be weighed with respect to their overall anticipated longevity and quality of life, because the presence of a spinal lesion may accompany more disseminated malignancy. Patients with a limited life expectancy because of widespread and aggressive metastatic tumors who are poorly responsive to medical therapy may not benefit from major spinal reconstructive procedures. Factors such as overall health, nutritional status, medical comorbidities, aggressiveness of the primary cancer, and extent of preop-erative neurologic deficits should be weighed when planning treatment.
Surgical therapy of cervical metastatic disease has evolved over the last decade, from primarily decompres-sive laminectomy to a more direct anterior approach to vertebral body metastasis. Metastatic disease most commonly involves the vertebral body, and reconstruction after anterior corpectomy is required for stability. Tumors involving the vertebral body of the subaxial spine can be approached readily via a standard anterior neck dissection with a transverse cervical incision. Intraoperative planning should include fiberoptic intubation, skeletal traction, and spinal cord monitoring, as with cases of traumatic instability. Pre-operative embolization may be useful for minimizing blood loss in extremely vascular tumors such as thyroid or renal metastases. Additional posterior stabilization, such as lateral mass screw/rod constructs, should be considered for supplementation of the anterior construct if significant kyphotic deformity or severe three-column instability is present. Posterior stabilization is particularly important for lesions at the cervicothoracic junction because of the higher risk of progressive kyphosis with anterior reconstruction and stabilization alone.
Numerous techniques have been reported for stabilization and reconstruction of the cervical spine after vertebral body resection for tumor. Interbody fusion with either auto-graft or allograft bone, with or without anterior plate stabilization, has been well described. The main advantage of using bone graft for reconstruction in patients with spinal metastasis is the proven durability of the construct after fusion has occurred in patients who are expected to survive longer than 6 months. Although achieving a solid bony fusion would be most desirable to prevent "wearing-out" of the construct, there are some disadvantages with the use of bone in these circumstances.
First, although fusion must be obtained for long-term stability, numerous factors usually work against the possibility of successful fusion in these patients, including previous or planned radiation therapy or chemotherapy and malnutrition. The ubiquity of such factors in patients with spinal metastases results in a significant risk of pseudoarthrosis and early construct failure. Second, locally recurring tumor can invade the graft and result in late failure, even if successful fusion occurs. Third, harvesting of iliac crest bone for grafting can result in significant postoperative pain and morbidity. Consequently, the use of bone for reconstruction should be limited only to patients who are judged onco-logically to have an expected survival of more than 6 months.
Numerous reports have been published regarding the use of PMMA for reconstruction since it was first described by Scoville and co-workers in 1967, when they reported the use of PMMA for spinal stabilization in a patient with metastatic lymphoma involving the cervical spine. Poly-methylmethacrylate-assisted reconstruction is a reasonable alternative to bone grafting for most cancers because it achieves immediate stabilization after radical tumor
ablation. It also is relatively inexpensive and easy to use. Unlike bone graft, PMMA is unaffected by the tumor and appears to be safe in patients who subsequently undergo radiation therapy. Results of the initial use of PMMA as a simple spacer were disappointing, with reports of graft dislodgment. This prompted a search for better methods to augment fixation of PMMA to the adjacent vertebral bodies with a variety of materials, including Steinmann pins, internal screws, and K-wires.
Sundaresan et al. performed reconstruction with PMMA and Steinmann pins in 101 patients with vertebral metas-tases. After the corpectomy, Steinmann pins are placed into the vertebral bodies above and below the level of the resection, and PMMA is poured into the resection cavity (Fig. 1). Gelfoam or fat is placed over the dura to protect against thermal injury from the exothermic polymerization reaction, and saline irrigation is used to dissipate the heat of polymerization. Pain relief was obtained in 85% of patients, and the overall ambulation rate increased from 55% to 78% postoperatively. Titanium screws can be used instead of Steinmann pins, which have ferromagnetic properties (Fig. 2A). Alleyne and co-workers advocated this technique as having the advantage of producing fewer imaging artifacts on postoperative CT and MRI. However, complications of graft dislodgement and pin migration were still reported.
The use of various hook and rod systems was then advocated to reduce the rate of dislodgement. Harrington described the use of a Knodt distraction rod and hooks to provide dynamic fixation for PMMA and to restore vertebral body height (Fig. 3). The Knodt rods come in lengths of 4 to 10 cm and can be used for reconstruction of multiple vertebral bodies. The endplates of the corpectomy cavity are prepared with a high-speed drill and fashioned to accept both the rod and the hook. By turning the distraction rod, the hooks are anchored progressively into the desired positions in relation to the spine. Polymethyl-methacrylate is then placed in the corpectomy defect and packed firmly around the endplate. However, construct failures and devastating dislodgment of pins resulting in esophageal perforation and spinal cord injury continued to be reported.
Perrin and McBroom described a technique for PMMA incorporated about a fixation device that bridges the cor-pectomy defect. A stainless steel reconstruction plate ("Wellesley wedge") with 2-mm guide holes is contoured to fit the corpectomy defect (Fig. 4). Screws are used to secure the plate into the vertebral bodies above and below the corpectomy. Polymethylmethacrylate is then molded into the defect and placed around the plate.
Ono and co-workers described the use of a ceramic prosthesis in conjunction with PMMA to augment fixation. This prosthesis contains portals anteriorly, superiorly, and infe-riorly (see Fig. 2B, C). After corpectomy, anchor holes are created within the superior and inferior endplates to allow PMMA fixation. The prosthesis is then introduced into the defect, and PMMA is poured into the anterior portal of the prosthesis. Because there is no posterior portal, the spinal cord is protected during PMMA polymerization. Poly-methylmethacrylate fills the superior and inferior portals, allowing fixation in the anchor holes.
Coaxial Double-Lumen Polymethylmethacrylate Reconstruction
More recently, coaxial double-lumen PMMA reconstruction (the "chest tube technique") has become popular. This technique, which involves keyholing chest tubes into the adjacent vertebral bodies and impregnating them with PMMA, has been reported to yield excellent clinical results, particularly when combined with anterior plating or posterior instrumentation, as needed. This method has the advantage of providing a barrier between the PMMA cement and the adjacent dura, thus protecting the neural elements from direct thermal injury during the exothermic solidification of PMMA. It also protects the neural elements from compression by PMMA cement expansion.
Miller and co-workers described a technique in which PMMA is injected through a coaxial double-lumen chest tube interposed in the corpectomy defect (Fig. 5). A 28-French chest tube (inner chest tube) is cut to the length needed to span the defect, and a small hole is made in the center to allow the PMMA to be introduced into the chest tube. Small notches also are made at both ends of the chest tube to allow extrusion of PMMA to maximize the cement-bone contact. Next, a strip 1 cm wide is removed longitudinally from a 40-French chest tube (outer chest tube) and is placed between the inner chest tube (the one filled with PMMA) and the dura. This outer chest tube serves as a trough and catches PMMA that has extruded and spilled over from the inner chest tube during PMMA injection. When the PMMA has polymerized to a viscid consistency, the outer chest tube is removed. Once the PMMA has hard-
Figure 5. Coaxial double-lumen PMMA reconstruction. From Miller DJ, et al: Coaxial double-lumen methylmethacrylate reconstruction in the anterior cervical and upper thoracic spine after tumor resection. J Neurosurg 92[2 Suppl]:181, 2000. Used with permission.
ened completely, manual distraction of the cervical spine is released, allowing compression to ensue. An anterior cervical plate stabilization system is placed to prevent distraction failure.
Titanium Mesh Interbody Cages
The titanium mesh cage is a cylindrical interbody reconstruction device that is available in several shapes, configurations, and diameters (Fig. 6). It can be trimmed easily and custom fit to the vertebrectomy defect. The inside of the cage can be filled with autograft or allograft if the goal is bony fusion. For most cancer patients, we prefer to fill the cage with methylmethacrylate. This increases the surface area between the vertebral endplates and the titanium mesh cage. To prevent PMMA leakage through the mesh interstices, we place a chest tube around the mesh cage prior to implantation. This also prevents the complication of thermal injury to the spinal cord. The final construct is then augmented with anterior plate fixation.
Figure 6. Reconstruction after cervical corpectomy for a renal cell metastasis using titanium mesh interbody cage and chest tube filled with PMMA. A, Preoperative CT scan. B, Postoperative x-ray.
Figure 7. Squamous cell carcinoma of the lung metastatic to C3. A, Preoperative plain x-ray showing marked destruction of the C3 vertebral body and associated kyphotic deformity. B, Postoperative x-ray showing placement of the Telescopic Plate Spacer device into the C3 corpectomy defect, restoring anterior column height.
Telescopic Plate Spacer
The Telescopic Plate Spacer (TPS; Interpore Cross International) is a new option for spine surgeons confronted with the technical dilemma of how to reconstruct a cervical corpectomy defect after tumor surgery (Fig. 7). The device is a titanium, two-piece plate-spacer hybrid, which can be used in either one-or two-level corpectomy defects. The spacer portion of the device is placed into the defect with the set screw facing anteriorly. The device is distracted open until it fits snugly within the defect and maximal correction of kyphosis has been achieved. The set screw is then tightened to lock the spacer portion of the device permanently at the desired height. The spacer portion of the device is hollow and may be packed with bone graft, if desired. Whether it is possible to achieve bony fusion through the device, however, remains to be seen. The plate portion of the device is then fixed to the adjacent vertebral bodies with bone screws in a manner similar to that used with most standard anterior cervical plates. Through its telescoping effect, the device can be expanded to fit corpectomy defects to restore anterior column height and correct kyphotic deformity.
The TPS system provides immediate stabilization and allows for early mobilization, obviating the need for external orthosis. The device also obviates the need for the use of PMMA, thus eliminating the risks of thermal injury to the spinal cord. The ease of implantation of the TPS also may be helpful for surgeons who are not often confronted with this surgical dilemma. If additional stability is required, supplementary posterior stabilization may be indicated.
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In response to the many questions we received about acceptance of CONTEMPORARY NEUROSURGERY CME credits by the AANS, we are pleased to announce they meet the requirements for 2003 and 2004 and will be accepted and applied to the ABNS for members' Maintenance of Certification. We are working toward a permanent arrangement with the AANS that will secure acceptance of these credits for many years to come.
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