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.

FIGURE 50-1 A, Proton density and T2-weighted sagittal MRI of metastatic carcinoma of the breast to the T12 vertebral body with angulation and severe spinal cord compression. B and C, Postoperative lateral and anteroposterior radiographs after T12 vertebral body resection showing the placement of a rib bone graft, methylmethacrylate, and Kaneda instrumentation. (Arrow in C indicates spinal canal.) Postoperatively, the patient recovered full neurologic function and was pain free. In view of the isolated vertebral body involvement, it was believed that good long-term survival was possible (thus the use of additional bone graft in the reconstruction). The patient, however, died of systemic metastatic cancer 8 months postoperatively. D, Sagittal reconstruction CT scan and corresponding axial image of (E) a patient with plasmacytoma involving the L1 vertebral body. T2-weighted sagittal (F) and axial (G) MRIs of the same case. Images of the CT scan illustrate the bony destruction, whereas the MRIs show the spinal cord compression more accurately. H, Preembolization angiogram showing the vascular supply of the L1 lesion with a tumor blush. I, Postembolization angiogram with a significant reduction in tumor blush in the same case.

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.

Preoperative Angiography and Embolization

Angiography, with a view to embolization, is recommended for patients with known vascular tumors (e.g., melanoma, renal cell carcinoma, metastatic thyroid tumor, primary giant cell tumor) or in patients in whom imaging suggests a relatively vascular tumor. If these tumors are amenable to embolization, it should be performed no more than 48 hours before surgery. Waiting too long after embolization may result in recanalization. The expertise of the interventional neuroradiologist will influence greatly the impact of presurgical embolization by reducing intraoperative blood loss. Additional information concerning the vascular supply of the spinal cord can also be obtained. Performing a spinal angiogram, however, for the sole purpose of defining the anatomy is unwarranted.

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.^12,17–19 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.

FIGURE 50-2 Patient is in the lateral position, and a dorsolateral thoracotomy skin incision is placed below the scapula.

Incision and Exposure

The side of approach and the level of the spine that is involved are important factors in determining where to make the incision. To maximize resection, the decision to perform a right-sided or left-sided skin incision and approach should be determined by the side of the spine with greater tumor involvement. If neither side is predominantly involved by tumor, the spine is generally approached from the right side, at or above the T5 vertebral segment, to avoid the arch of the aorta. Below T5, the spine is generally approached from the left side to minimize retraction on the liver. Careful review of the axial images in order to appreciate the corridor of access between the great vessels and the lateral aspect of the spine is essential. This information may, in fact, push a surgeon to the other side and to tolerate the liver retraction.

Lesions involving the cervicothoracic (C7-T1), upper thoracic (T1-5), lower thoracic (T6-11), thoracolumbar (T12 and L1), and lumbar and sacral (L2 to sacrum) segments require specific approaches (see Table 50-1) and considerations that have been described in other chapters of this text.

Exposure

The pleura is sharply incised and reflected. A rib that overlies the level of the pathology in the midaxillary level is resected. The appropriate rib is identified using intraoperative imaging. The segmental vessels at the level of the pathology and of the vertebral bodies above and below the lesion (Fig. 50-3) are ligated and divided. Division of segmental vessels over the vertebral body in the middle of the body reduces the risk of vascular compromise of the spinal cord by taking advantage of collateral vessels from adjacent levels. The periosteum is reflected medially, and the anterior longitudinal ligament is identified.

FIGURE 50-3 Exposure of the thoracic spine after entry into the thoracic cavity and placement of a self-retaining chest retractor. The parietal pleura has been separated from the ribs and spinal column with the segmental vessels along the side of the vertebrae identified.

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.

FIGURE 50-4 After a thoracotomy via resection of a rib located one level rostrally, the pleura is reflected off the ventral spine. The segmental vascular bundles are isolated and ligated as shown. Vertebral decompression of the tumor begins by the excision of intervertebral discs above and below the involved vertebra. Following this, 1 to 2 cm of the rib head is drilled down to expose the ipsilateral pedicle.

FIGURE 50-5 Axial section through vertebra involved with spinal tumor showing the extent of bony decompression necessary to allow adequate tumor resection.

FIGURE 50-6 Remaining vertebra after bony decompression and tumor removal showing that the decompression extends from the ipsilateral pedicle to the contralateral pedicle.

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.

FIGURE 50-7 After tumor resection, the end plates and cancellous bone of adjacent vertebral bodies are removed to the degree shown (dotted line) using an angled high-speed drill or angled curettes.

Intraspinal Decompression

After adequate bony resection, decompression, and removal of all devitalized bone and tumor tissue, the posterior longitudinal ligament is resected to expose the dura mater that encloses the spinal cord and segmental nerve roots. Any tumor or bone impinging on the dural sac or nerve root is carefully removed to allow decompression of these structures. The goal of surgery should be radical tumor resection and decompression. In patients who have previously received RT, the posterior longitudinal ligament is frequently adherent to the dura mater and may be difficult to separate. In these cases, it may be advisable to leave it in situ. In most virgin cases the dissection plane between tumor and dura is easily exploited.

Complications Related to the Approach

A thoracotomy carries pulmonary risks such as atelectasis and pneumonia. The retroperitoneal exposure may injure the spleen, kidney, or ureter, and a prolonged postoperative ileus may occur. Any unrepaired defect in the abdominal wall or diaphragm may be the site of visceral herniation. Using vertebral body screws with manual confirmation of bicortical penetration requires considerable dissection of the contralateral aspect of the vertebral body, placing the aorta, inferior vena cava, and iliac vessels at risk if this is not done meticulously. Injury to the lumbar hypogastric plexus at L5 in males may be complicated by retrograde ejaculation. Chyle leak from damage to the thoracic duct is best managed with immediate repair.

Inadequate Spinal Decompression

Inadequate decompression or incomplete tumor resection reduces the chance of adequate neurologic recovery. It is important that the decompression be performed to the contralateral pedicle. Complete visualization of the dura mater and confirmation with intraoperative radiograph that the appropriate level has been decompressed are required.

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.

Dural Tears

Dural tear from direct surgical trauma may occur while the tumor is being dissected or because of erosion of the dura caused by the tumor. In these cases, the precise site of dural tear should be identified and the tear repaired with a nonabsorbable suture (e.g., 4-0 Nurolon [Ethicon]). In less discrete or poorly visualized dural tears, fibrin glue can be layered over the cerebrospinal fluid leakage site and allowed to adhere to underlying dura mater. A lumbar drain should be placed for 5 days postoperatively to assist dural closure and reduce cerebrospinal fluid leaks.

Excessive Epidural Bleeding or Bleeding from Tumor

Preoperative angiography and embolization of vascular tumors reduce the risk of such intraoperative bleeding. After careful identification and mobilization, segmental vessels above and below the corpectomy site should be ligated and cut to avoid bleeding from these vessels when the vertebral bodies adjacent to the corpectomy site are spread apart. Other sites of epidural bleeding should be identified, and hemostasis should be attained with bipolar coagulation. Epidural bleeding can be particularly troublesome and require the use of various packing agents such as hemostatic gelatin (Gelfoam, Baxter Healthcare, Glendale, CA) and thrombin. Dealing with epidural vessels by coagulation before sharp dissection is the optimal strategy. Tumor bleeding can also be difficult to address. Remember to remove all visible tumor, because the most frequent site of bleeding is from the tumor bed. Preoperative planning and gross total resection of the lesion is the best strategy for tumor bleeding. Tumor bleeding can also be controlled using various packing material as described earlier. Polymethylmethacrylate (PMMA) in the resection cavity can be used. The primary function is to reconstruct, but one of the secondary benefits will be from the thermal reaction of the cement, which can cauterize the remaining tissues.

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).

FIGURE 50-8 A, Proton density sagittal MRI scan illustrating an L1 burst fracture with compression of the conus. B and C, Postoperative anteroposterior and lateral radiographs after anterior decompression and stabilization using bone graft (combination of humeral allograft and rib autograft) and Kaneda instrumentation. Coronal (D) and sagittal (E) CT scan images showing an expandable cage for the reconstruction of a two-level corpectomy. The Kaneda system is added to the construct for additional support to the anterior and middle column. The arrows in (E) identify the Kaneda screws into the body above and below the cage, while the arrow in (D) shows the connecting rods.

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.^11,21–27 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

Reconstruction techniques aim to provide solid fixation of adjacent spinal segments. Failure of these constructs is usually the result of reconstruction material dislodging at proximal and/or distal ends where the material fits into adjacent spinal segments. Early spinal changes in the cancellous bone of adjacent vertebral segments, seen on postoperative MRI scans, can be an indication of potential failure of these regions to anchor the construct. Another important situation is one in which adjacent vertebral segments are involved with disease but are not collapsed and are not causing spinal cord compression. PMMA can be used to strengthen the adjacent bone. Alternatively, supplemental dorsal instrumentation may be required. The technique of vertebroplasty has grown significantly in popularity for osteopenic fractures in the elderly.^28–32 This technique can complement and add strength to a ventral or even dorsal construct.

Synthetic Constructs

The technique of Errico and Cooper,⁷ in which PMMA is pressure injected into a Silastic tube that is fitted against the vertebral bodies above and below, provides an ideally suited construct for patients with metastatic lesions (Fig. 50-9). Silastic tubing of varying diameters (typically 15–20 mm) is cut to a measured length (from the outer edge of the upper and lower troughs of adjacent vertebral segments to the corpectomy site). One 6-mm-diameter hole is made in the center of the tubing with a rongeur, and three small holes are made laterally, two at the rostral end and one at the caudal end. Small bites are also made at the ends of the tubing to allow extrusion of cement overflow. The three smaller lateral holes allow air bubbles and excess cement to flow out easily. The side of the Silastic tubing facing the spinal cord is free of the central and lateral holes to avoid cement extrusion into the spinal canal. The Silastic tubing is passed into the space between two adjacent vertebral bodies at the corpectomy site and positioned so that there is no bending of the tubing that could obstruct cement flow. Low-viscosity, slow-curing PMMA is prepared and is kept in a large 50-mL syringe. When it has become semiliquid, the PMMA is injected through the center hold of the Silastic tubing, filling the tubing until PMMA can be seen passing out from the ends of the tube (see Fig. 50-9). Certain PMMA mixtures are now available, allowing for more controlled timing of the reaction and more reliable handling characteristics. The tube must be observed carefully to avoid spilling the PMMA into the spinal canal. Curved Penfield dissectors can be used to protect the dural tube. As the PMMA in the Silastic tubing becomes harder, more PMMA is prepared and placed ventral and lateral to the Silastic tube until it is continuous with the borders of the upper and lower vertebrae. During polymerization and hardening of the PMMA, copious saline irrigation is used to help dissipate the heat. Hemostasis is attained with bipolar coagulation.

FIGURE 50-9 After the Silastic tubing is inserted into the spinal defect, a syringe is used to fill the tube with slow-curing, low-viscosity polymethylmethacrylate.

Using Silastic tubing instead of K-wires, in conjunction with PMMA, for reconstruction of the vertebral body defect has certain advantages. First, the pliable Silastic tubing can be positioned with its ends sitting against the graft beds of the rostral and caudal adjacent vertebrae. This ensures the tubing is anchored against the adjacent vertebral bodies and does not remain unanchored in an open defect, thus reducing the risk of extrusion of the cement into the spinal canal and enhancing fixation to the adjacent vertebral column. Second, passing PMMA into the cancellous bone of adjacent vertebral segments further reinforces the vertebral bodies above and below the corpectomy site. Third, the pliable plastic filled with hardened PMMA becomes a long rigid construct that encompasses the length of the corpectomy site defect to assist anchorage into adjacent vertebrae, which reduces the risk of the construct dislodging from this position.

Degree of Vertebral Involvement

Most forms of metastatic spinal disease usually involve the vertebral body. When there is significant involvement of the dorsal elements, dorsal resection of the pathology can be performed by laminectomy. The decision to decompress using a ventral or dorsal approach is based on the location of the pathology and the compression. Combined approaches are required when the destruction of the native spinal column is circumferential. Many surgeons prefer to proceed with ventral decompression initially because this approach will more often provide a greater degree of decompression. Dorsal instrumentation will supplement the ventral construct and can be done either in combination with the initial operation or in a delayed fashion. Circumferential stabilization is recommended to prevent subsequent spinal instability, spinal deformity, or excessive spinal movement that may predispose to loosening and dislodgement of the spinal construct at the corpectomy site. The length of the dorsal instrumentation will be based on the quality of the pedicular purchase and the overall alignment of the construct. Instrumentation should not be terminated in the midthoracic curve to minimize the chance of pulling out the screws at the end of the instrumentation. Added consideration is given to the transition zones at the cervicothoracic and thoracolumbar levels. Bridging of these areas is often required to reduce the chance of failure of the spinal segment adjacent to the construct.

Distraction

After initial vertebral decompression, vertebral distraction is attained by using a vertebral distracter or by applying distraction after placing vertebral screws.

Graft Site Preparation

The end plates of vertebral bodies adjacent to the decompression site are prepared to accept a graft. The underlying cancellous bone should not be exposed by complete removal of the end plates. Destruction of the end plates will lead to reduction of the mechanical strength of the vertebral body and increase the risk of the strength of the vertebral body. It will also increase the risk of the graft telescoping into or penetrating the weakened vertebral bodies. The rostral and caudal end plates are of different shapes. This difference must be kept in mind, and selective drilling must be used to ensure that the graft site has parallel surfaces with adequate cortical bone remaining to support the graft. One common mistake is the failure to remove sufficient ventral and dorsal end plate lip, resulting in a central gap between the bone graft and vertebral end-plate. Another mistake that has more serious consequences is the “ramp effect,” which occurs when excessive bone is removed from the ventral two thirds of the lower vertebral body. This excessive removal results in a graft site that is longer ventrally than dorsally, predisposing to ventral dislocation of the graft.

Grafting

A firm, well-fitted graft is the result of not only a well-prepared graft site but also a well-proportioned, appropriately sized bone graft. A caliper and depth gauge should be used to measure the length and depth of the graft site accurately to determine the dimensions of the bone strut. The depth of the graft site is measured from the dorsal cortex to the ventral cortex along the midline of the vertebral body. The length of the graft site is measured with the vertebral bodies maximally distracted and is the distance between the end plates.

A tricortical iliac crest bone graft can be used up to a two-level corpectomy. More extensive decompression may necessitate a humeral or fibular allograft. Such an allograft strut has greater biomechanical strength than an iliac crest, with an acceptable fusion rate. The high cortical bone content, however, means that it may take up to 1 year for the graft to incorporate.³³ A supplemental local autograft (e.g., from rib or vertebral body) enhances the rate of fusion when using allografts (see Fig. 50-8). If grafts are taken from the iliac crest, the osteotomies should be perpendicular to the surface to the iliac crest and parallel to each other. A double-bladed oscillatory saw is useful in obtaining parallel surfaces. When these grafts are to be used for subtotal or total vertebral body replacement, several extra millimeters should be taken to allow for further reshaping. In the midthoracic and upper thoracic spine, rib strut grafts taken at the time of the thoracotomy are usually adequate if combined with cages.

With the vertebral bodies distracted, the graft is gently placed into position and should fit without excessive force or hammering. Tactile inspection of the final position of the graft should be done using a blunt hook alongside the graft. Small pieces of cancellous bone can be gently impacted into the remaining gaps. However, care should be taken to avoid spinal canal compromise or compression of neural structures by these smaller pieces of bone. It is important to use a drill to remove any irregularities of the ventral surface of the vertebral bodies so that the plate can sit flush against them. A greater plate-to-bone contact allows increased structural stability of this construct.

Hemorrhage

Although hemorrhage cannot be totally avoided, it is important to minimize the amount of blood loss during fusion by giving special consideration to the following three factors:

Pseudarthrosis

Pseudarthrosis refers to a lack of bony union and may account for a poor clinical result. It is worth noting, however, that fibrous pseudarthrosis may limit spinal movement and allow a good clinical outcome with symptomatic relief. Moreover, even when bony fusion has occurred, patients can remain symptomatic. Meticulous attention to graft site preparation and use of autograft, where possible, enhances fusion rates. In cases of traumatic lesions, the supplementation of the fusion with a local vertebral body autograft, where possible, enhances fusion rates. In cases of traumatic lesions, the supplementation of the fusion with a local vertebral body autograft that is osteoinductive may be appropriate.

Harvesting Autogenous Iliac Crest Bone

The iliac crest is the most common site from which bone grafts are taken. Consideration of the following complications during this procedure may help reduce the donor site morbidity associated with this procedure.^35–38 Donor site pain is common and can continue to be a problem in one out of five patients, lasting up to 2 years postsurgery.³⁹

Cosmetic deformity can be a problem when full-thickness grafts are taken from the iliac crest. When larger grafts are taken and cosmetic deformity becomes a concern, three techniques are useful in preventing crest deformities: (1) The trapdoor method uses the crest as a hinge; (2) the subcrestal window avoids resection of the rostral margin of the crest;⁴⁰ and (3) oblique sectioning of the crest allows the crest to be reconstituted.^39,41 Reconstruction of the crest, using different techniques, has been described: rib,^42–44 bioactive apatite and wollastonite-containing glass ceramic,⁴⁵ or methylmethacrylate.⁴⁶ Although infection is not a major concern, it does occur occasionally. A deep wound infection at the iliac donor site is treated like other wound infections adjacent to bone. It will require drainage, irrigation, and appropriate antibiotic coverage. Hematoma is common at the wound site. Gelfoam or bone wax can be used, but microcrystalline collagen is best for reducing bleeding from cancellous bone.⁴⁷ Suction drainage, although not a proven method, may be used to reduce the incidence of wound hematomas. Gait disturbance, with a limp or abductor lurch as a result of considerable stripping of the outer table muscles, can cause hip abductor weakness. With bone graft taken from the dorsal crest, patients may have difficulty with hip extension, which is evident when climbing stairs or rising from a chair.

Stress fractures can occur after full-thickness grafts are taken from the ventral iliac crest.⁴⁸ Stress fractures, as a result of the pull from the sartorius and rectus femoris muscles, can be avoided by harvesting the graft well away from the anterior superior iliac spine.⁴⁹ Moreover, taking long strips of bone along the iliac crest increases the risk of ilium fracture.

Perforation of the peritoneum can occur with a ventral approach to the inner table of the iliac crest because the peritoneum is closely related to the inner surface of the abdominal wall and iliacus muscles.⁵⁰ Herniation of abdominal contents can occur after removal of full-thickness grafts that include the iliac crest.⁵¹

Placing the skin incision behind the anterior superior iliac spine can minimize injury to the lateral femoral cutaneous nerve. Anatomic variation of the lateral femoral cutaneous nerve places this nerve at risk in less than 10% when dissection is 3 cm dorsal to the anterior iliac spine.⁵²

T1 to T9

When the corpectomy involves only the thoracic spine, supplementary instrumentation is generally unnecessary because the thoracic spine, unlike the lumbar spine, is supported by the rib cage. However, if there is three-column involvement, additional instrumentation will be necessary (Fig. 50-10).³ For the upper thoracic spine (T1-3), ventral cervical plates can be used (Fig. 50-11).

FIGURE 50-10 A, Proton density and T2-weighted sagittal MRI scan showing a T4-5 fracture dislocation with angulation and spinal cord compression in a 24-year-old woman with an incomplete spinal cord injury. A left third rib thoracotomy approach was used to perform a ventral decompression and reconstruction with rib autograft. In view of the three-column injury with associated rib fractures, posterior instrumentation (AO Universal Spine System) was performed. B, Postoperative lateral radiographs show correction of the kyphotic deformity with posterior segmental stabilization.

FIGURE 50-11 A, Gadolinium-enhanced T1-weighted sagittal MRI scan of a patient with tuberculosis of the cervicothoracic junction showing vertebral body involvement of T1 and extension into the spinal canal with severe spinal cord compression and paraspinal extension. Surgical exposure of this lesion was achieved via a right-sided cervicosternotomy approach. B and C, Postoperative T1-weighted sagittal MRI scan and lateral cervical spine radiograph after vertebral body resection and stabilization with an iliac crest bone graft and Synthes plate. These axial CT scan images at T12 (D) and L2 (E) demonstrate the suboptimal screw placement (Kaneda system). The screws are convergent but do not engage the second cortex; the arrows show the gap. The CT scan images, sagittal (F) and corresponding axial images (G), show the bony destruction in this case of Pott disease at the T12 and L1 level. The MRIs, T2-weighted sagittal (H) and corresponding axial image (I), show the spinal cord compression. J and K, A postoperative CT scan demonstrates the anterior reconstruction with a titanium cage filled with autologous bone graft. This construct was subsequently complemented with posterior instrumentation using pedicle screws above and below the cage (not shown here).

T10 to L5

The T12 vertebral body and lumbar spine receive little or no additional support from the rib cage, and in this region there is a greater degree of extension of the spine with spinal motion. Ventral instrumentation is necessary to supplement the reconstruction and to prevent excessive extension that can lead to extrusion of the graft or synthetic construct.^13,53,54

Supplemental Ventral Instrumentation

The rationale for using ventral instrumentation can be understood best by considering the biomechanics of the ventral fixation device. Shono et al.⁵⁵ and Gertzbein⁵⁶ have described the biomechanics of thoracolumbar ventral fixation devices when loss of anterior and middle column integrity is present. The Kaneda device,⁵³ which has two cross-fixed rods linked to four vertebral body screws (see Figs. 50-1 and 50-8), allows rigid stabilization against forces of axial compression, flexion, extension, and rotation. The quadrangular construct created by the two independent rods linked by the two cross-fixed bars provides greater resistance to flexion-extension and rotation than a single-rod system such as the Zielke system. The insertion of the vertebral body screws in nonparallel (triangular) alignment controls ventral and downward displacement. In the ventrally destabilized spine, the Kaneda construct provides superior fixation compared with dorsal instrumentation (such as a laminar hook or pedicle screw system), especially against flexion and axial compression forces. The vertebral body screws should be placed in a triangular fashion to avoid pullout and the need to engage the contralateral cortical bone of the vertebral body (see Fig. 50-11). If disruption of dorsal elements is present, ventral instrumentation alone is insufficient to provide stability (see Fig. 50-10). Most important, regardless of the rigidity of instrumentation, the spinal construct will eventually fail unless solid bony fusion occurs. One of the key concepts of ventral fusion is that the bone graft should be placed under compression to allow greater graft stability and fusion to adjacent vertebral bodies.⁴¹

Osteomyelitis of the Spine

The most common infections of the spinal column are (1) infections caused by pyogenic organisms (Staphylococcus aureus and coliform bacilli are the most common pyogenic bacteria found), (2) infections caused by fungi (actinomycetes and blastomycetes are the most common organisms found), and (3) tuberculosis (Pott disease) (see Fig. 50-11).

These organisms usually reach the spinal column by hematogenous spread. The seeding of these infections is typically localized to the disc space because this avascular compartment is harder for the patient’s own immune system to control. This “disc”-centric pathology is important when reviewing the images and trying to distinguish infectious from neoplastic pathology. Infection becomes symptomatic as a result of neural compromise from an associated extradural abscess or bony deformity from vertebral collapse with adjacent bone overgrowth that compromises the spinal canal (gibbus formation).

Identification of predisposing factors for infection following spinal surgery has been described by Wimmer et al.⁶⁰ Medical conditions such as diabetes, obesity, corticosteroid therapy, chronic infection, and smoking were identified in patients with a higher rate of infection. Surgical variables such as previous spinal surgery, extended preoperative hospitalization (P < .001), and high blood loss (P < .01) were identified as risk factors. The role of prophylactic antibiotic administration has been demonstrated by Horwitz and Curtin⁶¹ to reduce wound infection with spinal surgery. Some institutions have adopted a prolonged duration of antibiotic doses for patients at higher risk, using the factors mentioned previously.

Patients with osteomyelitis usually have symptoms of back pain, local spinal tenderness, and paraspinal muscle spasm. Associated fever and leukocytosis are common. Erosion of several adjacent vertebral bodies with collapse and involvement of associated intervertebral discs is characteristic and an early radiographic finding on lateral and anteroposterior spine films. Bone scans are often positive at regions of vertebral infection, and the serum alkaline phosphatase level is often elevated.

In these infective cases, it is important to assess, using axial CT images, the degree of spinal canal narrowing from vertebral collapse or gibbus formation (see Fig. 50-11F and G). In the absence of spinal canal narrowing, an extradural abscess or granuloma is the likely cause of spinal symptoms. MRI or myelography to delineate neural (spinal cord or nerve root) compromise is also indicated for these patients before surgical decompression (see Figs. 50-11H to K).

Surgical decompression is indicated in patients with progressive symptoms of spinal cord compression. The thoracic region is the most common site of osteomyelitis, and dorsolateral spinal approaches (e.g., costotransversectomy) usually allow adequate spinal decompression. Occasionally, ventral decompressive procedures are necessary when there is (1) progressive spinal compression; (2) osteomyelitis of the cervical spine; (3) spinal infections with kyphotic angulation in the lower lumbar spine, in which a retroperitoneal approach with corpectomy can be performed; and (4) extensive involvement of the vertebral body that cannot be adequately decompressed by the dorsolateral approach (see Fig. 50-11).

The method of vertebral decompression and reconstruction is similar to that described earlier. The use of autogenous bone is favored in the setting of osteomyelitis. Internal fixation use is controversial. Some surgeons advocate its use in the setting of osteomyelitis provided that a good local debridement is achieved. For pyogenic infections, appropriate intravenous antibiotics are necessary for 4 to 6 weeks, followed by oral antibiotics, until the infection resolves both clinically and radiographically.

Some patients with tuberculosis of the spine and mild neurologic signs of spinal cord compression improve with antituberculous drugs and rest, and without requiring surgical decompression. However, close neurologic follow-up is required to ensure that symptoms are not progressive. It is important to remember that spinal infections can result in spinal cord symptoms without actual spinal cord compression. These symptoms occur as a result of vascular thrombosis secondary to the inflammatory process. It is important, then, to confirm radiologically any evidence of spinal cord compression because these patients do not benefit from surgical decompression.

Kyphotic Deformities

Ventral corpectomy and fusion allow the correction of severe, symptomatic deformities. Surgical exposures are performed as described earlier, depending on the spinal level of the deformity. A ventral release with section of the anterior longitudinal ligament and discectomies is helpful for correcting the deformity. The adjacent discs involved in the kyphosis are identified and excised, and autologous bone (cortical iliac bone, section of rib, or fibula) is used for bone struts. This may be supplemented by ventral instrumentation to allow early ambulation of the patient. Most severe fixed kyphotic deformities require supplemental dorsal instrumentation and fusion.

Resection of Hemivertebra

A hemivertebra may become symptomatic and cause a severe, progressive deformity of the spine with neurologic compromise.⁹ This usually occurs when the anomaly lies low in the lumbar spine and results in congenital scoliosis with the hemivertebra as the apical part of the curve. The hemivertebra is resected ventrally to dorsally, back to the level of the epidural space, with the base of the pedicle also resected. An autologous bony strut graft with ventral instrumentation can be used for stability. Either during this procedure or during a second operation, a dorsal approach is used to resect the dorsal elements of the hemivertebra.

Thoracic and Thoracolumbar Fractures

These fractures can be approached by a ventral, ventrolateral (see Figs. 50-8 and 50-10), dorsolateral, or dorsal approach depending on certain features.^20,62–64 When lesions are ventral in the thoracic spine, available options for surgical exposure that allow decompression and stabilization include costotransversectomy, a lateral extracavitary approach, a transthoracic extrapleural approach, or a transthoracic transpleural approach. The authors favor the latter approach when neural decompression is an important goal, as in the patient with incomplete spinal cord injury (see Figs. 50-8 and 50-10). For burst fractures at the thoracolumbar junction, a transthoracic/retroperitoneal (10th rib approach) exposure is used to achieve ventral decompression and reconstruction (see Fig. 50-8). For midlumbar fractures (L2 or L3), a retroperitoneal approach is used. Low lumbar fractures (L4 or L5) are approached via a dorsolateral approach because the nerve roots may be retracted with greater facility, allowing easier decompression.

The transthoracic and retroperitoneal approaches allow a single-stage procedure with decompression and removal of pathologic material ventral to the dura mater over several vertebral segments and reconstruction with bone graft and instrumentation. Three-column injuries necessitating the use of ventral decompression require supplemental dorsal instrumentation (see Fig. 50-10).