Ventral and Ventrolateral Spine Decompression and Fusion

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Chapter 50 Ventral and Ventrolateral Spine Decompression and Fusion

Ventral spinal decompression was described by Royle1 as early as 1928. This approach remained unused until 1956, when Hodgson and Stock2 reported the use of ventral spinal decompression in the treatment of tuberculous lesions. A progressive increase in the use of ventral and ventrolateral approaches for spinal decompression in treating various spinal lesions such as tuberculosis, pyogenic osteomyelitis, kyphotic deformities, neoplasms (primary and metastatic), and burst fractures36 has been observed. The types of ventral approaches used for different spinal levels are summarized in Table 50-1. Ventral and ventrolateral decompression principles for spinal tumors are discussed in depth. This discussion is followed by the management of other types of spinal pathology that may be treated through a ventral decompression.

TABLE 50-1 Classification of Ventral Surgical Approaches

Spinal Segment Surgical Approach
Cervicothoracic C7-T2 (see Fig. 50-11) Extended ventral cervical (division of strap muscles)
Transsternal
Cervicosternotomy (“trapdoor” approach)
Upper thoracic T2-5 (see Fig. 50-10) High dorsolateral thoracotomy (third-rib approach with mobilization of scapula)
T6-12 Dorsolateral thoracotomy
Thoracolumbar T12-L2 (see Figs. 50-2 to 50-7) Transthoracic/retroperitoneal with 10th to 12th rib resection; division of diaphragm
Lumbar Retroperitoneal/flank
L2-5 Transabdominal
Lumbosacral L5-sacrum Ventral retroperitoneal (“pelvic brim” approach)

Spinal Tumors

The surgical management of patients with spinal tumors and associated spinal cord compression has shifted from a laminectomy approach to ventral approaches with ventral decompression.3,79 Because most spinal tumors are located ventrally, a laminectomy can limit the degree of ventral resection and can exacerbate, or worsen, existing spinal instability associated with tumors that have destroyed spinal body segments. Several authors10,11 have reported that the results of ventral decompression of spinal tumors with spinal cord compression are significantly better in most cases when compared with radiation therapy (RT) alone or in conjunction with laminectomy. Patchell et al. demonstrated the superiority of combined surgery and radiation in their randomized study.12 Ambulation as their primary end point was significantly better in the combined surgery and radiation cohort. Dorsolateral approaches can also provide some degree of ventral spinal decompression, with the advantage that they allow for both ventral and dorsal decompression and dorsal stabilization with a single exposure. Because of the limited access of the contralateral ventral dural sac, however, this exposure is more suitable in cases with unilateral spinal canal and vertebral involvement. The results of ventral decompression suggest that this is an effective method to preserve and improve neurologic function in patients with neural compromise from primary and metastatic tumors of the thoracic and lumbar spine.3,4,13,14

The principal indications for ventral decompressive surgery in patients with ventrally located spinal tumors are (1) progressive neurologic deficits, (2) pathologic fracture or impending spinal instability, and (3) mechanical or compressive pain. In rare circumstances, resection of a lesion to make the diagnosis is required. A CT-guided needle biopsy can and should be undertaken if the lesion has characteristics of a primary tumor. The issue of pain can be controversial; if the etiology of the pain is from compression of the neural tissues or mechanical instability, justification for decompression and fixation can be made. The authors have intervened surgically on terminal patients with a life expectancy of 3 to 4 months for whom conservative measures have failed to provide sufficient pain relief. Life expectancy is therefore an important factor to consider, but one must appreciate the collective limitations in arriving at an exact figure.

The radiosensitivity of the tumor plays an important role in overall management. Radiosensitive tumors (e.g., lymphoma, myeloma, Ewing sarcoma, neuroblastoma) can be treated with radiation therapy initially, if the cord compression is the result of epidural tumor alone. Surgical decompression should be the initial treatment when a significant degree of compression can be attributed to bony or ligamentous fragments or spinal deformity, as a result of destruction by tumor. In cases of failed radiation therapy with persistent or recurrent spinal cord compression, surgical intervention is also recommended. The increased complications associated with operating on a previously radiated site also favor surgery before radiation. Surgical decompression can be considered for radiation-resistant tumors such as melanoma or renal cell carcinoma and intermediate radiosensitive tumors such as those of the lung, breast, or prostate. The rate of clinical progression provides the surgeon with valuable information when deciding the optimal timing of intervention. Rapid progression of symptoms is best managed with surgery because the effects of radiation can initially be associated with swelling. The medical status of the patient and ability to tolerate the surgery are also taken into consideration. The issue of radiation sensitivity of tumors is changing. The field of radiation treatment, much like the surgical field, has seen significant advances. Stereotactic delivery of radiation and image modulation are just two examples.

Preoperative Assessment

Initially, plain spine radiographs (anteroposterior and lateral) are used to determine the level and extent of tumor involvement. The spinal alignment can also be observed from these films. A CT scan without intravenous contrast at the appropriate spinal levels allows better definition of the degree of bony destruction of the spinal column. Although MRI is less precise than CT in outlining bony destruction, it provides the most precise means for illustrating the site and degree of spinal cord compression by tumor or soft tissues (Fig. 50-1). Myelography and postmyelography CT scan can be used when MRI is contraindicated or unavailable. The use of contrast for determining the degree of vascularity of the tumor with either CT scan or MRI is still at the research level. CT angiographies are becoming more useful in the spine as their resolution is increasing.

To avoid complications from intraoperative and postoperative instability of the spinal column, it is important to assess the spinal stability before performing a vertebral decompression. Stability can be considered in terms of the three-column theory, after the extent of bony destruction produced by tumor has been determined from imaging.15,16 Single-column involvement can be considered relatively stable. The additive destabilizing effects of decompression, however, must factor into the decision-making process.

Anterior column and middle column involvement is the most common finding in symptomatic patients with spinal tumors and is frequently associated with some degree of vertebral body collapse and bony retropulsion into the spinal canal (see Fig. 50-1A). If these conditions are treated by corpectomy, with a strut graft used for fusion (see Figs. 50-1B and C), stability of the spinal column can be achieved.

Careful review of the degree of involvement of the dorsal elements is required. The need for augmentation of ventral fixation with dorsal instrumentation will be based on the integrity of the laminae, lateral masses, pars interarticularis, and facets. Corpectomy and vertebral replacement techniques can result in persistent dorsal element instability if overdistraction and opening of the facets are achieved. This instability can prevent subsequent fusion and result in failure of the ventral fixation. The ease with which distraction can be obtained following decompression can also provide the surgeon with information regarding the degree of dorsal instability. Intraoperative radiographs can be taken to ensure the proper amount of distraction. In cases when the dorsal instability is deemed significant, dorsal stabilization should be undertaken. Discretion of the surgeon will be used to decide if and when the dorsal stabilization procedure is required.

When planning surgery for spinal tumors, an assessment of stability must also take into account angulation and alignment.16 Higher failure rates will be observed with a poorly aligned construct. It is also important to consider the nature of the tumor in terms of its capacity to infiltrate and destroy bony tissue and its response to RT or chemotherapy.

Surgical Management

Intraoperative Monitoring and Anesthetic Management

The authors recommend electrophysiologic monitoring, if available, including somatosensory and motor evoked potentials, at all vertebral levels involving the spinal cord. Electromyography (EMG) monitoring is also useful in the lumbar region, if segmental pedicular fixation is contemplated. Monitoring setup time and cost are definite drawbacks to this type of technology, although its use is generally supported in the literature.12,1719 In approaches of the upper and middle thoracic spine, a double-lumen endotracheal tube allows the lung in the operative field to be deflated, improving the surgical exposure. In lesions of the lower thoracic and thoracolumbar regions, the lung can be retracted easily. Invasive arterial pressure monitoring and central venous pressure (CVP) monitoring and access are recommended in order to address any blood loss during the surgery.

Positioning

Patients are positioned in the full lateral decubitus position (Fig. 50-2) with an axillary roll placed under the dependent axilla to prevent neurovascular compromise. A mild flexion in the hip will assist mobilization of the psoas muscle should the exposure require it.

Spinal Decompression

Spinal decompression requires a sequential approach that can be divided into four stages, which are discussed in the next four sections.

Vertebral Body Decompression

The intervertebral discs above and below the involved vertebral body are identified and resected initially by sharp dissection (Fig. 50-4). Disc material is cleared with curettes and pituitary rongeurs. Removing the rib head will allow identification of the ipsilateral pedicle and its continuation into the vertebral body. The pedicle is an important marker for the orientation and position of the spinal canal. Using sharp curettes, rongeurs, and a high-speed drill, the vertebral body is resected ventrally to dorsally, except for a rim of the ventral portion of the vertebral body. This rim protects the aorta and inferior vena cava from accidental trauma. Resection of the vertebral body can progress as far as the opposite pedicle (Figs. 50-5 and 50-6), and the entire dorsal aspect of the vertebral body can be removed. Sufficient bone needs to be removed to clear the posterior longitudinal ligament of any compression of the dura. The dissection can also be continued dorsolaterally to allow decompression of the spinal nerve roots. The tumor involvement and the quality of the residual bone for instrumentation will determine the extent of bony removal. Techniques to augment the strength of the purchase into the bone are discussed in subsequent paragraphs.

Rostrocaudal Dissection

Special care is afforded to the cartilaginous end plates and the central regions of cancellous bone of vertebral bodies adjacent to the corpectomy site. Removal is performed using a small high-speed bur or curette (Fig. 50-7) or osteotomes and rongeurs, depending on the bone consistency. This allows troughs to be created in the vertebral bodies above and below the corpectomy site to allow subsequent reconstruction with a bone graft, an implant, or an acrylic graft. Preparing the end plates to accommodate the construct requires special attention. When the construct involves bone, either autograft or allograft, an eventual fusion will be desired. In this circumstance the end plates require adequate vascular supply for achieving fusion. The structural integrity of the graft can also fail if it is suboptimal or radiated. Methylmethacrylate (MMA), on the other hand, will not fuse, and the overall construct strength can be weakened by aggressive removal of the end plates. The risk of telescoping and the graph imploding into the vertebral body can also occur when the end plates are destroyed. MMA, however, will tolerate radiation.

Avoiding Complications during Spinal Decompression

Neurologic Injury

A carefully staged approach to spinal decompression with adequate exposure and identification of segmental vessels, nerve roots, and the dural tube markedly reduces the risk of nerve root and spinal cord injury. Nuwer20 concluded that intraoperative neurophysiologic monitoring is a cost-effective way of reducing the potential for a neurologic deficit. Intraoperative information is valuable not only to the prognosis but also by altering intraoperative and postoperative management. Hardware revision and removal during the operation may be performed on the basis of intraoperative neurophysiologic changes.

Spinal Reconstruction

Graft Material

The appropriate type of material to use for spinal column reconstruction depends on the nature of the lesion and the patient’s life expectancy. In cases of trauma, for benign lesions, or for patients with malignant tumors who have a relatively long life expectancy (>2 years), reconstruction is best when using autogenous bone from the iliac crest or rib for single vertebral body defects. If two or more vertebral levels are involved with the neoplasm, an allograft (e.g., from the fibula or humerus) can be used. It is often useful to supplement the allograft strut with local autograft bone (Fig. 50-8).

In patients with malignant disease and a short life expectancy, autogenous bone grafts have certain disadvantages: (1) If life expectancy is less than 1 year, solid bony fusion over the long term is unnecessary; (2) the use of adjunctive radiation and chemotherapy will slow or prevent the bony fusion needed for stability; (3) any remaining local tumors may infiltrate the bone graft and weaken the construct; and (4) autogenous donor sites may not be suitable because of tumor involvement.

For patients with an expected survival of 18 months or less, a synthetic construct using PMMA with or without titanium cages can be used. Expandable cages with only titanium construct have also been used to provide ventral support and reconstruction in difficult cases (see Fig. 50-8D and E). Biomechanical studies looking at intervertebral fixation have shown resistance of the implants to cyclical fatigue within typical normal physiologic loading and superior reduction of intervertebral motion and increased spinal stiffness.11,2127 The use of expandable vertebral protheses or cages is gaining popularity. An example of such a device can be found with the X-mesh cage (DePuy Spine, Raynham, MA).

Reconstruction Technique

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