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Thoracolumbar Spine Trauma
Thoracolumbar Spine Trauma Archit Patel, MD,* Zoe Brown, MD,* Peter G. Whang, MD,† and Alexander R. Vaccaro, MD, FACS* Thoracic and lumbar fractures are highly prevalent injuries. No accepted operative treatment protocol exists for the management of burst fractures in this region, and anterior, posterior, and combined approaches all have been successfully described in the literature. Appropriate surgical strategy is dependent on an accurate assessment of spinal stability, the neurologic status of the patient, and the morphology of injury. Posterior instrumentation using distraction and ligamentotaxis is a well-accepted method for addressing unstable thoracolumbar burst fractures with or without an associated neurologic deficit in which direct decompression is not required. Anterior decompression, however, remains the preferred method of treatment for burst fractures with incomplete neurologic deficits in association with significant canal occlusion and relative sparing of the posterior ligamentous complex. In this work, we explore the indications, contraindications, and technical complexities of posterior decompression with pedicle screw instrumentation, distraction, and ligamentotaxis, as well as anterior decompression and interbody fusion. Oper Tech Orthop 17:190-198 © 2007 Elsevier Inc. All rights reserved. KEYWORDS thoracolumbar burst fracture, posterior distraction and ligamentotaxis, anterior decompression and instrumentation
T
horacic and lumbar fractures are highly prevalent, representing nearly 90% of all traumatic spine injuries. Thoracolumbar burst fractures occur when the vertebral body is subjected to a significant axial and possibly flexion force vector that brings about the failure of the anterior vertebral body in compression.1 This region is uniquely susceptible to this mechanism of injury as the result of its location between the stiff, kyphotic thoracic spine and the more mobile, lordotic lumbar region. The resultant change in sagittal balance renders this area extremely vulnerable to axial forces. Unlike purely compressive fractures in which the posterior vertebral body wall remains intact, burst injuries are typically associated with retropulsed fragments of bone or disk, some degree of canal occlusion, and a high incidence of neurologic deficits. The successful diagnosis and management of thoracolumbar fractures is dependent on an accurate assessment of spinal stability, a concept defined by the integrity of the spine and its supporting structures as well as the neurologic status
*Department of Orthopaedic Surgery, Thomas Jefferson University and The Rothman Institute, Philadelphia, PA. †Yale University, New Haven, CT. Address reprint requests to Alexander R. Vaccaro, MD, FACS, Department of Orthopaedic Surgery and The Rothman Institute, 925 Chestnut Street, 5th Floor, Philadelphia, PA 19107. E-mail: [email protected]
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of the patient. In the absence of any clinical or radiographic evidence of neural compression or instability, most thoracolumbar injuries may be treated nonoperatively with external immobilization and early ambulation (Fig. 1). Operative intervention, however, should be considered when patients exhibit spinal instability, severe deformities, or incomplete neurologic injuries. The goals of surgery are to restore spinal stability through fracture stabilization and to improve functional outcome by decompressing involved neural structures. No standard treatment protocol for thoracolumbar fractures exists and anterior, posterior, and combined techniques all have been successfully described. In certain clinical scenarios, posterior instrumentation techniques best facilitate fracture reduction and subsequent arthrodesis. Indirect decompression of the spinal canal through distraction and ligamentotaxis, a process that effectively shifts the retropulsed bony fragments anteriorly away from the neural structures, may concurrently be accomplished. The posterior-only approach has gained popularity with the development of modern pedicle screw-based systems that provide reliable fixation, thereby increasing the rigidity of the anterior and posterior elements, and improving the magnitude of axial and rotational forces tolerated by the spine. An anterior approach is preferred in other clinical scenarios because it provides excellent visualization for the decom-
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191 columbar Injury Classification and Severity Score as a method to more precisely define fracture stability and thus guide clinical management. This classification system emphasizes the morphology of injury, the integrity of the posterior ligamentous complex, and the neurologic status of the patient. The validity and reproducibility of this model recently have been validated.5 Comprehensive diagnostic studies using multiple modalities must be obtained during preoperative planning. Plain x-rays may underestimate canal compromise by as much as 20% and, thus, computed tomography scans are essential for assessing vertebral body comminution, and bony anatomy before reconstruction.6 Magnetic resonance imaging also may be useful in evaluating ligamentous structures and identifying pathologic conditions such as herniated disks, myelomalacia, and the presence of epidural hematomas. Significant kyphosis or loss vertebral body height at the level of the fracture are radiographic findings suggestive of posterior instability (Fig. 2).7 An isolated posterior instrumented fusion is most appropriate for an unstable burst fracture without associated neu-
Figure 1 Magnetic resonance demonstrating a L3 burst fracture resulting in 50% canal occlusion.
pression of neural elements and easy access for the reconstruction of the anterior column with a load-sharing construct. The introduction of more rigid anterior instrumentation has made it possible to increase the stability of interbody implants while minimizing the number of levels to be fused.
Indications and Contraindications for Surgical Intervention Identifying the most appropriate surgical technique for a particular thoracolumbar burst fracture is based on several important considerations, including the degree of sagittal deformity, the radiographic appearance of the spinal canal, the neurologic examination of the individual, and any other evidence of spinal instability. Concurrent injuries as well as medical comorbidities influence this process. Although the Denis and AO schemes are currently the most widely accepted classification systems for thoracolumbar burst fractures, they exhibit only fair interobserver and intraobserver reliabilities.2,3 As a response to these deficiencies, Vaccaro and coworkers4 recently developed the Thora-
Figure 2 A sagittal T1 magnetic resonance image demonstrating a L3 burst fracture with a significant kyphotic deformity.
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Figure 3 A lateral plain radiograph after an open reduction and transpedicular decompression of a symptomatic L5 burst fracture with a nerve root deficit.
rologic deficits in which direct decompression is not indicated. A posterior procedure also may be performed for an acute burst fracture associated with neurologic injury or moderate canal occlusion in which distraction and ligamentotaxis is likely to reduce displaced bony fragments. Multiple studies have shown that canal compromise may be reduced by up to 50%, usually to less than 20% of the total canal area8-11 with this technique alone (Fig. 3). In patients with complete thoracic-level spinal cord injuries in which meaningful neurologic recovery is highly unlikely, a posterior arthrodesis may be indicated to provide immediate stability, reestablish proper alignment, and retard the progression of further deformity. This strategy also may be considered when a fracture involving the posterior elements produces neurologic deficits, in which case, a laminectomy may be necessary to release entrapped roots or repair traumatic dural tears. In rare instances, high burst fractures (ie, between T2 and T4) will require a posterior decompression because of the risks of anterior thoracotomy. Flexion-distraction and soft-tissue Chance injuries with disruption of the posterior ligamentous complex also may be addressed with the same posterior approach; the instrumentation acts to buttress the deficient posterior tension band.
A. Patel et al Similarly, fracture-dislocations and shear injuries with extensive translational or rotational instability are more easily addressed via a posterior approach using pedicle screws. A commonly encountered contraindication to posterior instrumentation with distraction and ligamentotaxis is a burst fracture with significant canal occlusion and impingement of neural elements. In the setting of canal compromise greater than 67%, indirect reduction techniques are not as effective because the anular attachments to the extruded fragments are less likely to be intact (Fig. 4).12 A second distinct contraindication is temporal. Multiple reports have shown that the results of posterior decompression using distraction and ligamentotaxis deteriorate as early as 3 days after the initial injury, suggesting that this intervention must be completed promptly before any fracture consolidation has occurred.8,13 In addition, posterior fusion with pedicle screws may not be technically feasible in patients with pedicles limited by atypical morphology, small bony dimensions, or traumatic fractures. Alternatively, an anterior approach permits an unobstructed view of the thecal sac and remains the most reliable method for achieving decompression in the patient with incomplete neurologic deficits who demonstrates significant canal occlusion on axial imaging studies. Anterior procedures also are indispensable for stabilizing burst fractures with substantial vertebral body comminution, where the use of load-sharing strut grafts or other interbody devices may correct a collapsed, kyphotic segment. Widely accepted indications for anterior surgery currently include retropulsed fragments occupying more than 67% of the total canal area, extensive comminution of the vertebral column in conjunction with a significant kyphotic deformity, and a delay in operative treatment longer than 4 days.14 In addition, any traumatic disk herniation causing symptomatic
Figure 4 A transaxial soft-tissue computed tomography scan demonstrating greater than 70% canal occlusion. Note the bilateral posterior laminar fractures.
Thoracolumbar spine trauma compression of the spinal cord or nerve roots are often best managed with an anterior approach. Patients with subacute fractures who have exceeded the documented 3- to 5-day window in which posterior distraction is most effective or those who continue to have symptomatic compression after posterior procedures may be candidates for delayed anterior decompression and arthrodesis, which has been shown to improve neurologic outcome months or even years later.15 Because the long-term success of interbody fusion techniques is largely dictated by the resistance of the posterior tension band to distraction forces, stand-alone anterior procedures may not be appropriate for injuries with significant posterior ligamentous disruption. Patients with thoracolumbar burst fractures with concomitant chest or abdominal injuries may not tolerate an anterior thoracolumbar exposure. Similarly, any serious medical comorbidity such as pulmonary disease or morbid obesity may prohibit the use of an anterior approach. In particular, severe osteoporosis is associated with graft impaction, hardware failure, and a significant rate of nonunion and sagittal malalignment.
Surgical Technique: Posterior Instrumentation Using Distraction and Ligamentotaxis After general endotracheal tube intubation, the patient is carefully logrolled into the prone position on a radiolucent frame (eg, Jackson table). All bony prominences are padded to prevent skin breakdown, and the abdomen is maintained tension free to minimize intra-abdominal pressure and any bleeding from the epidural venous plexus. The knees should be placed in a slightly flexed position to relieve any traction on the sciatic nerves. To avoid injury to the brachial plexus and peripheral nerves, the shoulders must remain in less than 90° of abduction. Lateral plain films with intraoperative pedicle markers are usually sufficient for visualization of the fractured segment and accurate intraoperative pedicle screw placementp; however, fluoroscopy may prove useful in this setting. In patients who are neurologically intact or have incomplete spinal cord lesions, we recommend intraoperative somatosensoryevoked potential and transcranial electric motor-evoked potential monitoring to provide real-time neurologic data during reduction maneuvers and instrumentation. The patient is prepped and draped in the standard sterile fashion, incorporating the iliac crests into the surgical field if harvesting autogenous bone. A standard midline skin incision is made over the fracture continued down to the level of the deep fascia. The fascia is incised on both sides of the involved spinous processes, and a subperiosteal exposure is performed laterally, beyond the facet joints, to the tips of the transverse processes that are within the intended fusion construct.
Pedicle Screw Instrumentation The starting point for instrumentation in the thoracic spine usually can be identified lateral to a vertical line bisecting the
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Figure 5 A tranaxial thoracic computed tomography scan demonstrating a potential complication of thoracic pedicle screw placement. Note the lateral breach of the left pedicle screw and its close proximity to the aorta.
facet joint along the upper third of the transverse process. The landmarks for pedicle screw placement are the transverse process, the pars interarticularis, and the facet joint. Access to the lumbar pedicles is achieved via the lateral aspect of the facet joint where it intersects a line passing through the middle of the transverse process. A high-speed burr is advanced 3 to 5 mm into the bone and a curette or awl is inserted to cannulate the pedicle, using fluoroscopy or static plain radiography with guide pins to verify correct angulation in all planes. The course and endpoint of the pedicle tract is palpated with a probe to ensure that there are no cortical breaches through any of the pedicle walls. Preoperative axial computed tomography images of the pedicles are used to approximate screw diameter, and the length may be obtained from a depth gauge (Fig. 5). As a screw of the appropriate size is being introduced, lateral fluoroscopy may be used to adjust its trajectory in the sagittal plane.
Rod Placement and Distraction/Ligamentotaxis Reduction After pedicle screw instrumentation, the rods are cut to span all of the instrumented levels and contoured to reproduce the normal sagittal curvature of the thoracolumbar spine. Once the rods are secured within the heads of the pedicle screws using connecting caps, the caudal ends are fixed and distraction is applied across the fracture. This maneuver restores vertebral body height and applies tension to the anulus and posterior longitudinal ligament, generating an anteriorly directed force that indirectly reduces the retropulsed fragments by ligamentotaxis. The remaining connecting caps are tightened over the rods, and the entire segment is locked in this lengthened position to maintain the fracture reduction. We recommend linking the rods with a cross connector either in
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194 the middle or at both ends of the rod to improve the rigidity of the construct.
Fusion Bed Preparation and Closure The laminae and facet joints at the levels to be fused are cleared of all soft tissue and decorticated using gouges or a high-speed burr. After meticulous hemostasis has been achieved, the entire operative field is irrigated and bone graft material is packed along all exposed bony surfaces. A drain is placed and the wound is closed in layers. Postoperatively, the patient is immobilized in a TLSO for approximately 3 months and is encouraged to ambulate as soon as possible.
Because the curvature of the rod will determine the degree of deformity correction, accurate contouring is necessary to prevent displacement at the fracture site. The rod should be straight in the coronal plane and should restore normal physiologic alignment in the sagittal plane to avoid postoperative “flat-back” syndrome. Reduction maneuvers should be performed in a controlled, deliberate fashion to avoid iatrogenic injury to the neural elements. Intraoperative correction may be monitored using fluoroscopy. Finally, to limit the potential for degenerative changes and deformity adjacent to the fusion construct, the facet joints and ligamentous structures of the uninvolved levels should not be damaged.
Complications Pearls and Pitfalls Some pearls and pitfalls should be taken into consideration when planning surgery. A general listing follows. Posterior distraction and ligamentotaxis should be performed within 72 hours of the time of injury, before any bony consolidation of the fracture has occurred. Fixation of only the levels immediately above and below the fracture does not provide sufficient stability for injuries at the thoracolumbar junction. Short segment fixation produces high rates of hardware failure and progressive deformity.16 This strategy, however, may be appropriate in the lower lumbar spine or in patients undergoing circumferential fusions. Longer constructs (2 levels above and 2 levels below) are more appropriate for a posterior-only approach because of their superior rigidity. This is particularly important in osteoporotic patients and in the setting of extensive fracture comminution. If the starting hole of the pedicle is difficult to locate, a laminotomy may be performed inferomedial to the superior articular facet to permit direct palpation of the pedicle from within the spinal canal. When using anterior–posterior (AP) and lateral flouroscopy, the tip of the curette or awl should not extend beyond the medial border of the pedicle on the AP view before reaching the posterior margin of the vertebral body on the lateral view. This reduces the risk of cortical injury to the medial pedicle wall. If the medial pedicle wall is intact on direct palpation, the screw trajectory does not need to be verified again in the AP view. Fluoroscopy equipment may be kept in the lateral position until instrumentation is complete. Thoracic pedicles that are too small to accommodate screws may be cannulated using a lateral extrapedicular approach; this method requires greater medial angulation to avoid a cortical breach of the lateral pedicle or vertebral body. If self-tapping screws are not used, the screw tract should be undertapped by 1 mm. Laminar hooks may be used to supplement pedicle screws at the ends of a long fusion construct. Polyaxial pedicle screws facilitate placement of the rods within the screw heads. However, posted monoaxial screws may allow for greater distraction and deformity correction. Because these distraction techniques will effectively lengthen the construct, it is important that the rod be cut slightly longer than measured.
Although the treatment of thoracolumbar burst injuries using posterior stabilization and indirect reduction has been shown to be relatively safe, this technique is nonetheless associated with significant complications. The incidence of iatrogenic neurologic injury is 1% and may occur during instrumentation or manipulation of the spinal cord and roots17; postoperative epidural hematoma may similarly cause neural element compression. Inadvertent violation of the anterior cortex during pedicle screw insertion may damage vascular or visceral structures, with devastating consequences. All dural tears, whether traumatic or iatrogenic in nature, should be closed primarily or reinforced with a dural patch. Persistent cerebrospinal fluid leaks may necessitate prolonged recumbency or the introduction of a lumbar subarachnoid drain. During reduction, as posterior forces are applied to the fractured segment, it is possible to overdistract the anterior column, leading to increased rates of pseudarthrosis and hardware failure, both of which may result in chronic pain or recurrent deformity. Approximately 10% of thoracolumbar fractures will become infected after posterior surgery and should be managed aggressively with culture-specific antibiotics as well as open irrigation and debridement when warranted.18 Finally, excessive blood loss may be poorly tolerated by patients with thoracolumbar spine fractures who frequently have sustained other critical injuries.
Surgical Technique: Anterior Decompression and Interbody Fusion General anesthesia is administered with the patient supine; for thoracic injuries necessitating a thoracotomy, single lung ventilation often is used to improve visualization of the fracture site and, thus, a double-lumen endotracheal tube frequently is inserted. The patient is placed in the lateral decubitus position with an airbag or external support to maintain alignment. The level of the fracture may be centered over the break in the table as increased flexion at the apex of the deformity will not only open the intercostal spaces and help with exposure but also will accommodate graft insertion by reducing the adjacent vertebral bodies. The arm ipsilateral to the surgical approach is elevated on a Mayo stand and a gel roll or intravenous fluid bag is introduced under the depen-
Thoracolumbar spine trauma dent axilla to protect the brachial plexus and avoid vascular compromise to the upper extremity. All bony prominences are padded. The surgical field should include most of the anterior chest wall and extend beyond the midline of the posterior spine. To decrease the risk of iatrogenic spinal cord injury, we advocate intraoperative neurophysiologic monitoring for individuals who are either neurologically intact or who present with incomplete deficits.
Operative Exposure Although a right thoracoabdominal or retroperitoneal exposure may be useful for certain fractures, a left-sided approach is advisable for most thoracolumbar injuries to circumvent the liver and minimize mobilization of the vena cava. The skin is sterilely prepped and draped, and an oblique incision is made laterally along the rib immediately cephalad to the injured segment and extended anteriorly toward the umbilicus. The intercostal muscles are divided and dissected from the rib, avoiding the neurovascular structures in the subcostal groove. We favor removing the rib by performing osteotomies at the costochondral junction anteriorly and at the costotransverse articulation posteriorly to obtain a wider exposure and to acquire local autograft for the fusion site. The margins of the incision are spread with a large self-retaining thoracotomy retractor and the lung is manually deflated. If the diaphragm is taken down to gain access to the thoracolumbar junction, the peripheral portion still attached to the chest wall should be marked with sutures in anticipation of repair at the time of wound closure. At this juncture, the spine should be easily visualized and, in most cases, an obvious palpable deformity is readily apparent; nevertheless, if any question remains, the location of the fracture should be confirmed by introducing a spinal needle into one of the disk spaces and obtaining a localizing radiograph. Once the segment of interest has been identified, the psoas muscle is released from the vertebral column. The parietal pleura is incised and bluntly elevated off the anterolateral aspect of the fractured body as well as the levels directly above and below the zone of injury. The corresponding segmental vessels are meticulously isolated, ligated, and transected to complete the exposure.
Corpectomy and Decompression Exposure of the transverse process and pedicle is completed by removing any residual rib head from the costotransverse articulation. A Penfield retractor or other blunt instrument may be placed within the foramen to define the boundaries of the pedicle and retract the surrounding soft tissues away from the posterior elements. The pedicle is thinned with a small burr and excised with a Kerrison rongeur to the level of the posterior vertebral body wall, revealing the anterior and lateral borders of the spinal canal. Discectomies are performed both cephalad and caudal to the fracture using a scalpel to incise the anular tissue and a pituitary rongeur or curette to extract the disk material. The corpectomy is initiated by splitting the disrupted body with an osteotomy, and bone is removed with a high-speed burr, rongeur, or curette and saved
195 for later implantation as cancellous autograft. A small-angled curette may be used to tease the retropulsed fragments away from the dura into the newly formed corpectomy defect. The anterior longitudinal ligament routinely is left intact, along with a rim of bone to preserve intersegmental stability and prevent graft dislocation. The medial wall of the contralateral pedicle serves as a guide for determining the transverse width of the vertebrectomy, and the decompression is not adequate until this anatomic structure is encountered. When the spinal canal is sufficiently decompressed, the thecal sac typically regains its normal bulbous appearance.
Deformity Reduction and Interbody Fusion In preparation for interbody fusion, the cartilaginous endplates of the vertebral bodies are eradicated with a burr or curette, providing a bleeding bony surface for vascular support of the graft. Care must be taken, however, to avoid the underlying subchondral bone and minimize the incidence of implant subsidence. A lamina spreader or distractor is inserted into the corpectomy site to reduce the deformity and restore sagittal alignment. Alternatively, an anteriorly directed force may be applied to the posterior elements to correct any kyphosis present at the fractured level. Autogenous tricortical bone harvested from the iliac crest is the gold standard for interbody fusion because it is the only material that supplies all 3 components necessary to achieve successful arthrodesis: osteoprogenitor cells, osteoinductive factors, and a structural osteoconductive matrix for bony ingrowth. Harvesting large amounts of iliac crest, however, is associated with significant morbidity, and several other options currently are available. Tibial and humeral allografts provide relatively large surface areas for fusion and expandable metal and synthetic cages composed of polyetheretherketone or carbon fiber exhibit tremendous compressive strength and are gaining popularity due to their ability to correct sagittal deformity once implanted and lengthened. Demineralized bone matrices and bone morphogenetic proteins also may provide adequate osteoinductive activity to replace cancellous bone. Without comparative studies establishing the superiority of one of these options over another, differences between these bone graft substitutes is insignificant in most trauma scenarios. A slot may be created in the endplates to accommodate an intended implant. If an autograft is not selected, a hollowed humeral or femoral allograft, or alternatively a metallic or synthetic cage matching the dimensions of the corpectomy defect is packed with cancellous bone and firmly seated between the vertebral bodies. The strut graft is compressed into its proper position by releasing the intervertebral distraction and reversing the break in the operative table.
Anterior Instrumentation Anterior spinal instrumentation systems have refined the operative management of thoracolumbar injuries by increasing stability of the construct and inhibiting graft extrusion and settling at the fracture site.19 As a result, these devices may improve fusion rates while limiting the number of levels in-
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196 cluded in the arthrodesis, especially with anterior-only procedures. Anterior instrumentation should always be placed posterolaterally on the vertebral column, away from the great vessels, to avoid catastrophic vascular injury. To create a relatively flat surface for the internal fixation, all of the osteophytes and end plate prominences must be eliminated with a burr or rongeur. An awl is used to cannulate the cephalad and caudal screw hole, maintaining a trajectory parallel to the end plates and thus avoiding adjacent disks. Although we recommend bicortical screws over unicortical fixation because of their superior pull-out strength,20 acute or delayed vascular complications may occur if the bolts protrude through the vertebral body. The screw lengths required to obtain bicortical purchase may be estimated from preoperative axial imaging studies. A plate or rod of the appropriate size is added to the screws and all elements are evaluated with intraoperative radiographs or fluoroscopy to ensure that internal fixation does not involve healthy disk spaces. The thecal sac and vascular structures are palpated to reconfirm that there is no impingement by the graft or instrumentation and compression is then applied across the fusion segment before final tightening of the construct.
Closure and Postoperative Care Any intraoperative bleeding must be resolved with bipolar cautery and thrombostatic agents before closure. The pleural cavity is irrigated and the lung re-expanded. A chest tube is placed to evacuate blood and air from the thoracic cavity. If previously opened, the diaphragm is securely repaired and the remaining ribs are approximated; anatomic closure of the wound is completed in multiple layers to obtain an airtight seal. The thoracostomy tube is connected to suction and removed only when the drainage has resolved and there is no further evidence of an air leak or pneumothorax. Postoperative dietary restrictions are strictly enforced until positive bowel sounds have returned. Patients are usually mobilized within 48 hours and are instructed to wear a thoracolumbosacral orthosis for a minimum of 3 months. Spinal cord injuries are best managed by a specialized multidisciplinary rehabilitation service.
Pearls and Pitfalls Patients with thoracolumbar fractures routinely present with other associated injuries; it is critical that any decision to proceed with anterior spinal surgery be made in conjunction with the general surgery team involved in their care. We recommend loupe magnification and fiberoptic headlight illumination for all anterior procedures to decrease the risk of iatrogenic injury to the dural sac and neural elements. To prevent any catastrophic vascular insults to the spinal cord during an anterior thoracolumbar exposure, segmental arteries may be temporarily clamped to ensure that there are no alterations in electrophysiologic monitoring signals before ligation. In general, the absolute minimum number of segmental vessels should be killed to safeguard cord perfusion. In most cases, the most significant compression of the spinal cord occurs superiorly at the level of the pedicles;
decompression should be initiated inferiorly, along the vertebral body, where there is a larger margin between the posterior wall and neural structures. After the pedicle is resected and the diskectomies completed, the thecal sac must be directly visualized to ensure that the posterior cortex remains untouched as the corpectomy bone is extracted. In addition, failure to continue the vertebrectomy to the contralateral pedicle may give rise to an unsatisfactory decompression. In addition to including the entire interpedicular space, an optimal decompression should also extend between both disk spaces. If the posterior longitudinal ligament does not bulge anteriorly in a uniform fashion even after thorough corpectomy has been performed, this layer may need to be excised to identify any remaining fragments of disk material or bone that may still be compressing the spinal canal. An undersized implant is prone to migration and may exacerbate any preexisting kyphosis and thus the interbody graft should be large enough to avoid extrusion and correct sagittal alignment. In the setting of a major kyphotic deformity, placing the strut graft more anteriorly in the corpectomy defect may provide greater biomechanical strength. Elderly patients may benefit from the use of their own autologous iliac crest or an allograft implant (iliac crest) whose modulus of elasticity is more similar to that of osteoporotic bone. A more rigid metallic device is more likely to undergo settling. The operating table may be tilted to accommodate a more anterior view of the vertebral column; however, during instrumentation, orientation must be maintained with the patient in a true lateral decubitus position. For stand-alone anterior procedures, 2 sets of rods or one plate is recommended to increase the stability across the fractured segment whereas a single anterior construct may be considered in patients undergoing supplementary posterior instrumentation as part of a combined approach. Finally, to avoid injury to the iliac vessels, anterior spinal instrumentation systems should rarely be employed below the L4 level.
Complications Patients undergoing anterior procedures are at risk for morbidity associated with an anterior thoracotomy such as pulmonary decompensation, damage to internal organs, vessel disruption, postoperative ileus, infection, and incisional herniation. Substantial bleeding from the corpectomy and the epidural plexus frequently is observed and should be managed with aggressive fluid resuscitation and intraoperative transfusion. Structural instability at the fracture site may result in a kyphotic deformity or pseudarthrosis. Although anterior instrumentation may improve the rigidity of the construct,21 the use of internal fixation is also subject complications including canal penetration, vascular insults, and hardware failure.
Outcomes Current clinical data are both mixed and inconclusive. Two recent randomized, prospective trials comparing the results of neurologically intact patients undergoing either operative
Thoracolumbar spine trauma or nonoperative management of stable thoracolumbar burst fractures emonstrated no significant differences between the 2 groups.11,22 In contrast, unstable injuries or those associated with neurologic deficits are more likely to benefit from surgical intervention, which may be performed anteriorly, posteriorly, or through a combined approach. Although there are currently no convincing data that establishes the superiority of one of these techniques over the others, many thoracolumbar fractures treated with posterior surgical approaches have produced excellent results with minimal complications.23 Several authors have suggested that posterior distraction instrumentation and ligamentotaxis may yield clinical and radiographic results equivalent to those achieved after anterior or circumferential procedures in the setting of unstable burst injuries (Fig. 6).24-26 A posterior-only approach, however, may predispose individuals with severe vertebral body disruption or comminution to instrumentation failure and progressive loss of sagittal alignment.27,28 Alternatively, several authors have shown that anterioronly techniques are an effective treatment for burst frac-
197 tures29-33; these methods also have been successfully applied to thoracolumbar injuries involving the anterior and posterior vertebral elements.34 Anterior decompression may facilitate greater recovery of motor strength and bowel/bladder function than posterior indirect reduction strategies.30,35 Anterior procedures performed months or even years after the original injury have been found to improve pain and neurologic deficits associated with post-traumatic kyphosis, even in revision situations involving previous posterior surgery.4 In one of the few prospective, randomized studies comparing outcomes of acute thoracolumbar burst fractures after either an anterior or a posterior surgical approach, patients with stand-alone anterior constructs were noted to have fewer complications and were less likely to require reoperation.26 Anterior instrumentation systems also appear to maintain sagittal alignment better than short-segment posterior fixation methods.36 Other reports, however, have demonstrated no significant differences between anterior and posterior techniques in terms of neurologic status and clinical outcomes.37,38 Current data are inconclusive and only reveal the need for further investigation to determine which surgical strategy is best suited for a particular thoracolumbar fracture.
Summary and Conclusions
Figure 6 A lateral plain radiograph after an AP decompression and fusion for a symptomatic L3 burst fracture. A metallic static cage was used as an anterior strut graft filled with local autogenous bone graft. With the use of a supralamina hook at L2 and an infralaminar hook at L4, only 2 motion segments were immobilized. This is an example of short segment internal fixation.
Although the majority of thoracolumbar fractures may be treated nonoperatively, unstable injuries or those associated with neurologic deficits may benefit from surgical intervention. A posterior-only approach has become a well-accepted method for managing unstable thoracolumbar burst fractures with or without an associated neurologic deficit. The application of distractive forces to a posterior construct may indirectly reduce retropulsed fragments through ligamentotaxis and effectively improve the degree of canal occlusion. Anterior decompression and interbody fusion, either alone or in conjunction with posterior techniques, remain the preferred method of treatment for patients who present with incomplete neurologic deficits without any significant involvement of the posterior ligamentous complex. An unobstructed exposure of the thecal sac facilitates the safe and effective decompression of the spinal cord and nerve roots and provides the opportunity to reconstruct the anterior column with a strut graft or interbody device to restore normal sagittal alignment. By increasing the stability at the fracture site, anterior instrumentation may enhance the rate of successful arthrodesis and prevent the development of progressive posttraumatic kyphosis. In many clinical situations, the optimal surgical approach for a specific thoracolumbar fracture remains a matter of some controversy. Clinical cohort studies are certainly warranted at this time to establish a comprehensive operative protocol for these complex injuries.
References 1. Vaccaro AR, Kim DH, Brodke DS, et al: Diagnosis and management of thoracolumbar and sacral spine fractures. Instru Course Lect 53:375385, 2004
198 2. Oner FC, Ramos LM, Simmermacher RK, et al: Classification of thoracic and lumbar spine fractures: Problems of reproducibility. A study of 53 patients using CT and MRI. Eur Spine J 11:235-245, 2002 3. Wood KB, Khanna G, Vaccaro AR, et al: Assessment of two thoracolumbar classification systems as used by multiple surgeons. J Bone Joint Surg Am 87:1423-1429, 2005 4. Vaccaro AR, Zeiller SC, Hurlbut RJ, et al: The thoracolumbar injury severity score: A proposed treatment algorithm. J Spinal Disord Tech 18:309-315, 2005 5. Vaccaro AR, Baron EM, Sanfilippo J, et al: Reliability of a novel classification system for thoracolumbar injuries: The Thoracolumbar Injury Severity Score. Spine 31:S62-S69, 2006 6. Keene JS, Fischer SP, Vanderby R Jr, et al: Significance of acute posttraumatic bony encroachment of the neural canal. Spine 14:799-802, 1989 7. Jacobs RR, Casey MP: Surgical management of thoracolumbar spinal injuries. General principles and controversial considerations. Clin Orthop Relat Res 189:22-35, 1984 8. Crutcher JP, Anderson PA, King HA, et al: Indirect spinal canal decompression in patients with thoracic and lumbar burst fractures by posterior distraction rods. J Spinal Disord 4:39-48, 1991 9. Harrington RM, Budorick T, Hoyt J, et al: Biomechanics of indirect reduction of bone retropulsed into the spinal canal. Spine 18:692-699, 1993 10. Sjostrom L, Karlstrom G, Pech P, et al: Indirect spinal canal decompression in burst fractures treated with pedicle screw instrumentation. Spine 21:113-123, 1996 11. Wood K, Butterman G, Mehbod A, et al: Operative compared with nonoperative treatment of thoracolumbar fracture without neurological deficit: A prospective, randomized study. J Bone Joint Surg Am 85:773-781, 2003 12. Gertzbein SD, Crowe PJ, Fazl M, et al: Canal clearance in burst fractures using the AO internal fixator. Spine 17:558-560, 1992 13. Willen J, Lindahl S, Irstam L, et al: Unstable thoracolumbar fractures. A study by CT and conventional roentgenology of the reduction effect of Harrington instrumentation. Spine 9:214-219, 1984 14. McCullen G, Vaccaro AR, Garfin SR: Thoracic and lumbar trauma: Rationale for selecting the appropriate fusion technique. Orthop Clin North Am 29:813-828, 1998 15. Bohlman HH, Kirkpatrick JS, Delamarter RB, et al: Anterior decompression for late pain and paralysis after fractures of the thoracolumbar spine. Clin Orthop Relat Res 300:24-29, 1994 16. McLain RF, Sparling E, Benson DR: Early failure of short-segment pedicle instrumentation for thoracolumbar fractures. A preliminary report. J Bone Joint Surg Am 75:162-167, 1993 17. Katonis P, Christoforakis J, Kontakis G, et al: Complications and problems related to pedicle screw fixation of the spine. Clin Orthop 411: 86-94, 2003 18. Rechtine GR, Bono PL, Cahill D, et al: Postoperative wound infection after instrumentation of thoracic and lumbar fractures. J Orthop Trauma 15:566-569, 2001 19. Gurr KR, McAfee PC, Shih CM: Biomechanical analysis of anterior and posterior instrumentation systems after corpectomy. A calf spine model. J Bone Joint Surg Am 70:1182-1191, 1988
A. Patel et al 20. Breeze SW, Doherty BJ, Noble PS, et al: A biomechanical study of anterior thoracolumbar screw fixation. Spine 23:1829-1831, 1998 21. An HS, Lim TH, You JW, et al: Biomechanical evaluation of anterior thoracolumbar spinal instrumentation. Spine 20:1979-1983, 1995 22. Shen WJ, Liu TJ, Shen YS: Nonoperative treatment versus posterior fixation for thoracolumbar junction burst fractures without neurologic deficit. Spine 26:1038-1045, 2001 23. Yue JJ, Sossan A, Selgrath C, et al: The treatment of unstable thoracic spine fractures with transpedicular screw instrumentation: A 3-year consecutive series. Spine 27:2782-2787, 2002 24. Danisa OA, Shaffrey CI, Jane JA, et al: Surgical approaches for the correction of unstable thoracolumbar burst fractures: A retrospective analysis of treatment outcomes. J Neurosurg 83:977-983, 1995 25. Been HD, Bouma GJ: Comparison of two types of surgery for thoracolumbar burst fractures: Combined anterior and posterior stabilization vs. posterior instrumentation only. Acta Neurochir (Wien) 141:349357, 1999 26. Wood KB, Bohn D, Mehbod A: Anterior versus posterior treatment of stable thoracolumbar burst fractures without neurologic deficit: a prospective, randomized study. J Spinal Disord Tech 18:S15-S23, 2005 27. Sasso RC, Cotler HB: Posterior instrumentation and fusion for unstable fractures and fracture-dislocations of the thoracic and lumbar spine. A comparative study of three fixation devices in 70 patients. Spine 18: 450-460, 1993 28. Slosar PJ Jr, Patwardhan AG, Lorenz M, et al: Instability of the lumbar burst fracture and limitations of transpedicular instrumentation. Spine 20:1452-1461, 1995 29. Kaneda K, Abumi K, Fujiya M: Burst fractures with neurologic deficits of the thoraco-lumbar spine. Results of anterior decompression and stabilization with anterior instrumentation. Spine 9:788-795, 1984 30. McAfee PC, Bohlman HH, Yuan HA: Anterior decompression of traumatic thoracolumbar fractures with incomplete neurological deficit using a retroperitoneal approach. J Bone Joint Surg Am 67:89-104, 1985 31. Kostuik JP: Anterior fixation for burst fractures of the thoracic and lumbar spine with or without neurological involvement. Spine 13:286293, 1988 32. Zdeblick TA, Shirado O, McAfee PC, et al: Anterior spinal fixation after lumbar corpectomy. A study in dogs. J Bone Joint Surg Am 73:527-534, 1991 33. Ghanayem AJ, Zdeblick TA: Anterior instrumentation in the management of thoracolumbar burst fractures. Clin Orthop Relat Res 335:89100 34. Sasso RC, Best NM, Reilly TM, et al: Anterior-only stabilization of three-column thoracolumbar injuries. J Spinal Disord Tech 18:S7-S14, 2005 35. Bradford DS, McBride GG: Surgical management of thoracolumbar spine fractures with incomplete neurologic deficits. Clin Orthop Relat Res 218:201-216, 1987 36. Sasso RC, Renkens K, Hanson D, et al: Unstable thoracolumbar burst fractures: Anterior-only versus short-segment posterior fixation. J Spinal Disord Tech 19:242-248, 2006 37. Esses SI, Botsford DJ, Kostuik JP: Evaluation of surgical treatment for burst fractures. Spine 15:667-673, 1990 38. Gertzbein SD: Scoliosis Research Society. Multicenter spine fracture study. Spine 5:528-540, 1992
T
horacic and lumbar fractures are highly prevalent, representing nearly 90% of all traumatic spine injuries. Thoracolumbar burst fractures occur when the vertebral body is subjected to a significant axial and possibly flexion force vector that brings about the failure of the anterior vertebral body in compression.1 This region is uniquely susceptible to this mechanism of injury as the result of its location between the stiff, kyphotic thoracic spine and the more mobile, lordotic lumbar region. The resultant change in sagittal balance renders this area extremely vulnerable to axial forces. Unlike purely compressive fractures in which the posterior vertebral body wall remains intact, burst injuries are typically associated with retropulsed fragments of bone or disk, some degree of canal occlusion, and a high incidence of neurologic deficits. The successful diagnosis and management of thoracolumbar fractures is dependent on an accurate assessment of spinal stability, a concept defined by the integrity of the spine and its supporting structures as well as the neurologic status
*Department of Orthopaedic Surgery, Thomas Jefferson University and The Rothman Institute, Philadelphia, PA. †Yale University, New Haven, CT. Address reprint requests to Alexander R. Vaccaro, MD, FACS, Department of Orthopaedic Surgery and The Rothman Institute, 925 Chestnut Street, 5th Floor, Philadelphia, PA 19107. E-mail: [email protected]
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of the patient. In the absence of any clinical or radiographic evidence of neural compression or instability, most thoracolumbar injuries may be treated nonoperatively with external immobilization and early ambulation (Fig. 1). Operative intervention, however, should be considered when patients exhibit spinal instability, severe deformities, or incomplete neurologic injuries. The goals of surgery are to restore spinal stability through fracture stabilization and to improve functional outcome by decompressing involved neural structures. No standard treatment protocol for thoracolumbar fractures exists and anterior, posterior, and combined techniques all have been successfully described. In certain clinical scenarios, posterior instrumentation techniques best facilitate fracture reduction and subsequent arthrodesis. Indirect decompression of the spinal canal through distraction and ligamentotaxis, a process that effectively shifts the retropulsed bony fragments anteriorly away from the neural structures, may concurrently be accomplished. The posterior-only approach has gained popularity with the development of modern pedicle screw-based systems that provide reliable fixation, thereby increasing the rigidity of the anterior and posterior elements, and improving the magnitude of axial and rotational forces tolerated by the spine. An anterior approach is preferred in other clinical scenarios because it provides excellent visualization for the decom-
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191 columbar Injury Classification and Severity Score as a method to more precisely define fracture stability and thus guide clinical management. This classification system emphasizes the morphology of injury, the integrity of the posterior ligamentous complex, and the neurologic status of the patient. The validity and reproducibility of this model recently have been validated.5 Comprehensive diagnostic studies using multiple modalities must be obtained during preoperative planning. Plain x-rays may underestimate canal compromise by as much as 20% and, thus, computed tomography scans are essential for assessing vertebral body comminution, and bony anatomy before reconstruction.6 Magnetic resonance imaging also may be useful in evaluating ligamentous structures and identifying pathologic conditions such as herniated disks, myelomalacia, and the presence of epidural hematomas. Significant kyphosis or loss vertebral body height at the level of the fracture are radiographic findings suggestive of posterior instability (Fig. 2).7 An isolated posterior instrumented fusion is most appropriate for an unstable burst fracture without associated neu-
Figure 1 Magnetic resonance demonstrating a L3 burst fracture resulting in 50% canal occlusion.
pression of neural elements and easy access for the reconstruction of the anterior column with a load-sharing construct. The introduction of more rigid anterior instrumentation has made it possible to increase the stability of interbody implants while minimizing the number of levels to be fused.
Indications and Contraindications for Surgical Intervention Identifying the most appropriate surgical technique for a particular thoracolumbar burst fracture is based on several important considerations, including the degree of sagittal deformity, the radiographic appearance of the spinal canal, the neurologic examination of the individual, and any other evidence of spinal instability. Concurrent injuries as well as medical comorbidities influence this process. Although the Denis and AO schemes are currently the most widely accepted classification systems for thoracolumbar burst fractures, they exhibit only fair interobserver and intraobserver reliabilities.2,3 As a response to these deficiencies, Vaccaro and coworkers4 recently developed the Thora-
Figure 2 A sagittal T1 magnetic resonance image demonstrating a L3 burst fracture with a significant kyphotic deformity.
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Figure 3 A lateral plain radiograph after an open reduction and transpedicular decompression of a symptomatic L5 burst fracture with a nerve root deficit.
rologic deficits in which direct decompression is not indicated. A posterior procedure also may be performed for an acute burst fracture associated with neurologic injury or moderate canal occlusion in which distraction and ligamentotaxis is likely to reduce displaced bony fragments. Multiple studies have shown that canal compromise may be reduced by up to 50%, usually to less than 20% of the total canal area8-11 with this technique alone (Fig. 3). In patients with complete thoracic-level spinal cord injuries in which meaningful neurologic recovery is highly unlikely, a posterior arthrodesis may be indicated to provide immediate stability, reestablish proper alignment, and retard the progression of further deformity. This strategy also may be considered when a fracture involving the posterior elements produces neurologic deficits, in which case, a laminectomy may be necessary to release entrapped roots or repair traumatic dural tears. In rare instances, high burst fractures (ie, between T2 and T4) will require a posterior decompression because of the risks of anterior thoracotomy. Flexion-distraction and soft-tissue Chance injuries with disruption of the posterior ligamentous complex also may be addressed with the same posterior approach; the instrumentation acts to buttress the deficient posterior tension band.
A. Patel et al Similarly, fracture-dislocations and shear injuries with extensive translational or rotational instability are more easily addressed via a posterior approach using pedicle screws. A commonly encountered contraindication to posterior instrumentation with distraction and ligamentotaxis is a burst fracture with significant canal occlusion and impingement of neural elements. In the setting of canal compromise greater than 67%, indirect reduction techniques are not as effective because the anular attachments to the extruded fragments are less likely to be intact (Fig. 4).12 A second distinct contraindication is temporal. Multiple reports have shown that the results of posterior decompression using distraction and ligamentotaxis deteriorate as early as 3 days after the initial injury, suggesting that this intervention must be completed promptly before any fracture consolidation has occurred.8,13 In addition, posterior fusion with pedicle screws may not be technically feasible in patients with pedicles limited by atypical morphology, small bony dimensions, or traumatic fractures. Alternatively, an anterior approach permits an unobstructed view of the thecal sac and remains the most reliable method for achieving decompression in the patient with incomplete neurologic deficits who demonstrates significant canal occlusion on axial imaging studies. Anterior procedures also are indispensable for stabilizing burst fractures with substantial vertebral body comminution, where the use of load-sharing strut grafts or other interbody devices may correct a collapsed, kyphotic segment. Widely accepted indications for anterior surgery currently include retropulsed fragments occupying more than 67% of the total canal area, extensive comminution of the vertebral column in conjunction with a significant kyphotic deformity, and a delay in operative treatment longer than 4 days.14 In addition, any traumatic disk herniation causing symptomatic
Figure 4 A transaxial soft-tissue computed tomography scan demonstrating greater than 70% canal occlusion. Note the bilateral posterior laminar fractures.
Thoracolumbar spine trauma compression of the spinal cord or nerve roots are often best managed with an anterior approach. Patients with subacute fractures who have exceeded the documented 3- to 5-day window in which posterior distraction is most effective or those who continue to have symptomatic compression after posterior procedures may be candidates for delayed anterior decompression and arthrodesis, which has been shown to improve neurologic outcome months or even years later.15 Because the long-term success of interbody fusion techniques is largely dictated by the resistance of the posterior tension band to distraction forces, stand-alone anterior procedures may not be appropriate for injuries with significant posterior ligamentous disruption. Patients with thoracolumbar burst fractures with concomitant chest or abdominal injuries may not tolerate an anterior thoracolumbar exposure. Similarly, any serious medical comorbidity such as pulmonary disease or morbid obesity may prohibit the use of an anterior approach. In particular, severe osteoporosis is associated with graft impaction, hardware failure, and a significant rate of nonunion and sagittal malalignment.
Surgical Technique: Posterior Instrumentation Using Distraction and Ligamentotaxis After general endotracheal tube intubation, the patient is carefully logrolled into the prone position on a radiolucent frame (eg, Jackson table). All bony prominences are padded to prevent skin breakdown, and the abdomen is maintained tension free to minimize intra-abdominal pressure and any bleeding from the epidural venous plexus. The knees should be placed in a slightly flexed position to relieve any traction on the sciatic nerves. To avoid injury to the brachial plexus and peripheral nerves, the shoulders must remain in less than 90° of abduction. Lateral plain films with intraoperative pedicle markers are usually sufficient for visualization of the fractured segment and accurate intraoperative pedicle screw placementp; however, fluoroscopy may prove useful in this setting. In patients who are neurologically intact or have incomplete spinal cord lesions, we recommend intraoperative somatosensoryevoked potential and transcranial electric motor-evoked potential monitoring to provide real-time neurologic data during reduction maneuvers and instrumentation. The patient is prepped and draped in the standard sterile fashion, incorporating the iliac crests into the surgical field if harvesting autogenous bone. A standard midline skin incision is made over the fracture continued down to the level of the deep fascia. The fascia is incised on both sides of the involved spinous processes, and a subperiosteal exposure is performed laterally, beyond the facet joints, to the tips of the transverse processes that are within the intended fusion construct.
Pedicle Screw Instrumentation The starting point for instrumentation in the thoracic spine usually can be identified lateral to a vertical line bisecting the
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Figure 5 A tranaxial thoracic computed tomography scan demonstrating a potential complication of thoracic pedicle screw placement. Note the lateral breach of the left pedicle screw and its close proximity to the aorta.
facet joint along the upper third of the transverse process. The landmarks for pedicle screw placement are the transverse process, the pars interarticularis, and the facet joint. Access to the lumbar pedicles is achieved via the lateral aspect of the facet joint where it intersects a line passing through the middle of the transverse process. A high-speed burr is advanced 3 to 5 mm into the bone and a curette or awl is inserted to cannulate the pedicle, using fluoroscopy or static plain radiography with guide pins to verify correct angulation in all planes. The course and endpoint of the pedicle tract is palpated with a probe to ensure that there are no cortical breaches through any of the pedicle walls. Preoperative axial computed tomography images of the pedicles are used to approximate screw diameter, and the length may be obtained from a depth gauge (Fig. 5). As a screw of the appropriate size is being introduced, lateral fluoroscopy may be used to adjust its trajectory in the sagittal plane.
Rod Placement and Distraction/Ligamentotaxis Reduction After pedicle screw instrumentation, the rods are cut to span all of the instrumented levels and contoured to reproduce the normal sagittal curvature of the thoracolumbar spine. Once the rods are secured within the heads of the pedicle screws using connecting caps, the caudal ends are fixed and distraction is applied across the fracture. This maneuver restores vertebral body height and applies tension to the anulus and posterior longitudinal ligament, generating an anteriorly directed force that indirectly reduces the retropulsed fragments by ligamentotaxis. The remaining connecting caps are tightened over the rods, and the entire segment is locked in this lengthened position to maintain the fracture reduction. We recommend linking the rods with a cross connector either in
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194 the middle or at both ends of the rod to improve the rigidity of the construct.
Fusion Bed Preparation and Closure The laminae and facet joints at the levels to be fused are cleared of all soft tissue and decorticated using gouges or a high-speed burr. After meticulous hemostasis has been achieved, the entire operative field is irrigated and bone graft material is packed along all exposed bony surfaces. A drain is placed and the wound is closed in layers. Postoperatively, the patient is immobilized in a TLSO for approximately 3 months and is encouraged to ambulate as soon as possible.
Because the curvature of the rod will determine the degree of deformity correction, accurate contouring is necessary to prevent displacement at the fracture site. The rod should be straight in the coronal plane and should restore normal physiologic alignment in the sagittal plane to avoid postoperative “flat-back” syndrome. Reduction maneuvers should be performed in a controlled, deliberate fashion to avoid iatrogenic injury to the neural elements. Intraoperative correction may be monitored using fluoroscopy. Finally, to limit the potential for degenerative changes and deformity adjacent to the fusion construct, the facet joints and ligamentous structures of the uninvolved levels should not be damaged.
Complications Pearls and Pitfalls Some pearls and pitfalls should be taken into consideration when planning surgery. A general listing follows. Posterior distraction and ligamentotaxis should be performed within 72 hours of the time of injury, before any bony consolidation of the fracture has occurred. Fixation of only the levels immediately above and below the fracture does not provide sufficient stability for injuries at the thoracolumbar junction. Short segment fixation produces high rates of hardware failure and progressive deformity.16 This strategy, however, may be appropriate in the lower lumbar spine or in patients undergoing circumferential fusions. Longer constructs (2 levels above and 2 levels below) are more appropriate for a posterior-only approach because of their superior rigidity. This is particularly important in osteoporotic patients and in the setting of extensive fracture comminution. If the starting hole of the pedicle is difficult to locate, a laminotomy may be performed inferomedial to the superior articular facet to permit direct palpation of the pedicle from within the spinal canal. When using anterior–posterior (AP) and lateral flouroscopy, the tip of the curette or awl should not extend beyond the medial border of the pedicle on the AP view before reaching the posterior margin of the vertebral body on the lateral view. This reduces the risk of cortical injury to the medial pedicle wall. If the medial pedicle wall is intact on direct palpation, the screw trajectory does not need to be verified again in the AP view. Fluoroscopy equipment may be kept in the lateral position until instrumentation is complete. Thoracic pedicles that are too small to accommodate screws may be cannulated using a lateral extrapedicular approach; this method requires greater medial angulation to avoid a cortical breach of the lateral pedicle or vertebral body. If self-tapping screws are not used, the screw tract should be undertapped by 1 mm. Laminar hooks may be used to supplement pedicle screws at the ends of a long fusion construct. Polyaxial pedicle screws facilitate placement of the rods within the screw heads. However, posted monoaxial screws may allow for greater distraction and deformity correction. Because these distraction techniques will effectively lengthen the construct, it is important that the rod be cut slightly longer than measured.
Although the treatment of thoracolumbar burst injuries using posterior stabilization and indirect reduction has been shown to be relatively safe, this technique is nonetheless associated with significant complications. The incidence of iatrogenic neurologic injury is 1% and may occur during instrumentation or manipulation of the spinal cord and roots17; postoperative epidural hematoma may similarly cause neural element compression. Inadvertent violation of the anterior cortex during pedicle screw insertion may damage vascular or visceral structures, with devastating consequences. All dural tears, whether traumatic or iatrogenic in nature, should be closed primarily or reinforced with a dural patch. Persistent cerebrospinal fluid leaks may necessitate prolonged recumbency or the introduction of a lumbar subarachnoid drain. During reduction, as posterior forces are applied to the fractured segment, it is possible to overdistract the anterior column, leading to increased rates of pseudarthrosis and hardware failure, both of which may result in chronic pain or recurrent deformity. Approximately 10% of thoracolumbar fractures will become infected after posterior surgery and should be managed aggressively with culture-specific antibiotics as well as open irrigation and debridement when warranted.18 Finally, excessive blood loss may be poorly tolerated by patients with thoracolumbar spine fractures who frequently have sustained other critical injuries.
Surgical Technique: Anterior Decompression and Interbody Fusion General anesthesia is administered with the patient supine; for thoracic injuries necessitating a thoracotomy, single lung ventilation often is used to improve visualization of the fracture site and, thus, a double-lumen endotracheal tube frequently is inserted. The patient is placed in the lateral decubitus position with an airbag or external support to maintain alignment. The level of the fracture may be centered over the break in the table as increased flexion at the apex of the deformity will not only open the intercostal spaces and help with exposure but also will accommodate graft insertion by reducing the adjacent vertebral bodies. The arm ipsilateral to the surgical approach is elevated on a Mayo stand and a gel roll or intravenous fluid bag is introduced under the depen-
Thoracolumbar spine trauma dent axilla to protect the brachial plexus and avoid vascular compromise to the upper extremity. All bony prominences are padded. The surgical field should include most of the anterior chest wall and extend beyond the midline of the posterior spine. To decrease the risk of iatrogenic spinal cord injury, we advocate intraoperative neurophysiologic monitoring for individuals who are either neurologically intact or who present with incomplete deficits.
Operative Exposure Although a right thoracoabdominal or retroperitoneal exposure may be useful for certain fractures, a left-sided approach is advisable for most thoracolumbar injuries to circumvent the liver and minimize mobilization of the vena cava. The skin is sterilely prepped and draped, and an oblique incision is made laterally along the rib immediately cephalad to the injured segment and extended anteriorly toward the umbilicus. The intercostal muscles are divided and dissected from the rib, avoiding the neurovascular structures in the subcostal groove. We favor removing the rib by performing osteotomies at the costochondral junction anteriorly and at the costotransverse articulation posteriorly to obtain a wider exposure and to acquire local autograft for the fusion site. The margins of the incision are spread with a large self-retaining thoracotomy retractor and the lung is manually deflated. If the diaphragm is taken down to gain access to the thoracolumbar junction, the peripheral portion still attached to the chest wall should be marked with sutures in anticipation of repair at the time of wound closure. At this juncture, the spine should be easily visualized and, in most cases, an obvious palpable deformity is readily apparent; nevertheless, if any question remains, the location of the fracture should be confirmed by introducing a spinal needle into one of the disk spaces and obtaining a localizing radiograph. Once the segment of interest has been identified, the psoas muscle is released from the vertebral column. The parietal pleura is incised and bluntly elevated off the anterolateral aspect of the fractured body as well as the levels directly above and below the zone of injury. The corresponding segmental vessels are meticulously isolated, ligated, and transected to complete the exposure.
Corpectomy and Decompression Exposure of the transverse process and pedicle is completed by removing any residual rib head from the costotransverse articulation. A Penfield retractor or other blunt instrument may be placed within the foramen to define the boundaries of the pedicle and retract the surrounding soft tissues away from the posterior elements. The pedicle is thinned with a small burr and excised with a Kerrison rongeur to the level of the posterior vertebral body wall, revealing the anterior and lateral borders of the spinal canal. Discectomies are performed both cephalad and caudal to the fracture using a scalpel to incise the anular tissue and a pituitary rongeur or curette to extract the disk material. The corpectomy is initiated by splitting the disrupted body with an osteotomy, and bone is removed with a high-speed burr, rongeur, or curette and saved
195 for later implantation as cancellous autograft. A small-angled curette may be used to tease the retropulsed fragments away from the dura into the newly formed corpectomy defect. The anterior longitudinal ligament routinely is left intact, along with a rim of bone to preserve intersegmental stability and prevent graft dislocation. The medial wall of the contralateral pedicle serves as a guide for determining the transverse width of the vertebrectomy, and the decompression is not adequate until this anatomic structure is encountered. When the spinal canal is sufficiently decompressed, the thecal sac typically regains its normal bulbous appearance.
Deformity Reduction and Interbody Fusion In preparation for interbody fusion, the cartilaginous endplates of the vertebral bodies are eradicated with a burr or curette, providing a bleeding bony surface for vascular support of the graft. Care must be taken, however, to avoid the underlying subchondral bone and minimize the incidence of implant subsidence. A lamina spreader or distractor is inserted into the corpectomy site to reduce the deformity and restore sagittal alignment. Alternatively, an anteriorly directed force may be applied to the posterior elements to correct any kyphosis present at the fractured level. Autogenous tricortical bone harvested from the iliac crest is the gold standard for interbody fusion because it is the only material that supplies all 3 components necessary to achieve successful arthrodesis: osteoprogenitor cells, osteoinductive factors, and a structural osteoconductive matrix for bony ingrowth. Harvesting large amounts of iliac crest, however, is associated with significant morbidity, and several other options currently are available. Tibial and humeral allografts provide relatively large surface areas for fusion and expandable metal and synthetic cages composed of polyetheretherketone or carbon fiber exhibit tremendous compressive strength and are gaining popularity due to their ability to correct sagittal deformity once implanted and lengthened. Demineralized bone matrices and bone morphogenetic proteins also may provide adequate osteoinductive activity to replace cancellous bone. Without comparative studies establishing the superiority of one of these options over another, differences between these bone graft substitutes is insignificant in most trauma scenarios. A slot may be created in the endplates to accommodate an intended implant. If an autograft is not selected, a hollowed humeral or femoral allograft, or alternatively a metallic or synthetic cage matching the dimensions of the corpectomy defect is packed with cancellous bone and firmly seated between the vertebral bodies. The strut graft is compressed into its proper position by releasing the intervertebral distraction and reversing the break in the operative table.
Anterior Instrumentation Anterior spinal instrumentation systems have refined the operative management of thoracolumbar injuries by increasing stability of the construct and inhibiting graft extrusion and settling at the fracture site.19 As a result, these devices may improve fusion rates while limiting the number of levels in-
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196 cluded in the arthrodesis, especially with anterior-only procedures. Anterior instrumentation should always be placed posterolaterally on the vertebral column, away from the great vessels, to avoid catastrophic vascular injury. To create a relatively flat surface for the internal fixation, all of the osteophytes and end plate prominences must be eliminated with a burr or rongeur. An awl is used to cannulate the cephalad and caudal screw hole, maintaining a trajectory parallel to the end plates and thus avoiding adjacent disks. Although we recommend bicortical screws over unicortical fixation because of their superior pull-out strength,20 acute or delayed vascular complications may occur if the bolts protrude through the vertebral body. The screw lengths required to obtain bicortical purchase may be estimated from preoperative axial imaging studies. A plate or rod of the appropriate size is added to the screws and all elements are evaluated with intraoperative radiographs or fluoroscopy to ensure that internal fixation does not involve healthy disk spaces. The thecal sac and vascular structures are palpated to reconfirm that there is no impingement by the graft or instrumentation and compression is then applied across the fusion segment before final tightening of the construct.
Closure and Postoperative Care Any intraoperative bleeding must be resolved with bipolar cautery and thrombostatic agents before closure. The pleural cavity is irrigated and the lung re-expanded. A chest tube is placed to evacuate blood and air from the thoracic cavity. If previously opened, the diaphragm is securely repaired and the remaining ribs are approximated; anatomic closure of the wound is completed in multiple layers to obtain an airtight seal. The thoracostomy tube is connected to suction and removed only when the drainage has resolved and there is no further evidence of an air leak or pneumothorax. Postoperative dietary restrictions are strictly enforced until positive bowel sounds have returned. Patients are usually mobilized within 48 hours and are instructed to wear a thoracolumbosacral orthosis for a minimum of 3 months. Spinal cord injuries are best managed by a specialized multidisciplinary rehabilitation service.
Pearls and Pitfalls Patients with thoracolumbar fractures routinely present with other associated injuries; it is critical that any decision to proceed with anterior spinal surgery be made in conjunction with the general surgery team involved in their care. We recommend loupe magnification and fiberoptic headlight illumination for all anterior procedures to decrease the risk of iatrogenic injury to the dural sac and neural elements. To prevent any catastrophic vascular insults to the spinal cord during an anterior thoracolumbar exposure, segmental arteries may be temporarily clamped to ensure that there are no alterations in electrophysiologic monitoring signals before ligation. In general, the absolute minimum number of segmental vessels should be killed to safeguard cord perfusion. In most cases, the most significant compression of the spinal cord occurs superiorly at the level of the pedicles;
decompression should be initiated inferiorly, along the vertebral body, where there is a larger margin between the posterior wall and neural structures. After the pedicle is resected and the diskectomies completed, the thecal sac must be directly visualized to ensure that the posterior cortex remains untouched as the corpectomy bone is extracted. In addition, failure to continue the vertebrectomy to the contralateral pedicle may give rise to an unsatisfactory decompression. In addition to including the entire interpedicular space, an optimal decompression should also extend between both disk spaces. If the posterior longitudinal ligament does not bulge anteriorly in a uniform fashion even after thorough corpectomy has been performed, this layer may need to be excised to identify any remaining fragments of disk material or bone that may still be compressing the spinal canal. An undersized implant is prone to migration and may exacerbate any preexisting kyphosis and thus the interbody graft should be large enough to avoid extrusion and correct sagittal alignment. In the setting of a major kyphotic deformity, placing the strut graft more anteriorly in the corpectomy defect may provide greater biomechanical strength. Elderly patients may benefit from the use of their own autologous iliac crest or an allograft implant (iliac crest) whose modulus of elasticity is more similar to that of osteoporotic bone. A more rigid metallic device is more likely to undergo settling. The operating table may be tilted to accommodate a more anterior view of the vertebral column; however, during instrumentation, orientation must be maintained with the patient in a true lateral decubitus position. For stand-alone anterior procedures, 2 sets of rods or one plate is recommended to increase the stability across the fractured segment whereas a single anterior construct may be considered in patients undergoing supplementary posterior instrumentation as part of a combined approach. Finally, to avoid injury to the iliac vessels, anterior spinal instrumentation systems should rarely be employed below the L4 level.
Complications Patients undergoing anterior procedures are at risk for morbidity associated with an anterior thoracotomy such as pulmonary decompensation, damage to internal organs, vessel disruption, postoperative ileus, infection, and incisional herniation. Substantial bleeding from the corpectomy and the epidural plexus frequently is observed and should be managed with aggressive fluid resuscitation and intraoperative transfusion. Structural instability at the fracture site may result in a kyphotic deformity or pseudarthrosis. Although anterior instrumentation may improve the rigidity of the construct,21 the use of internal fixation is also subject complications including canal penetration, vascular insults, and hardware failure.
Outcomes Current clinical data are both mixed and inconclusive. Two recent randomized, prospective trials comparing the results of neurologically intact patients undergoing either operative
Thoracolumbar spine trauma or nonoperative management of stable thoracolumbar burst fractures emonstrated no significant differences between the 2 groups.11,22 In contrast, unstable injuries or those associated with neurologic deficits are more likely to benefit from surgical intervention, which may be performed anteriorly, posteriorly, or through a combined approach. Although there are currently no convincing data that establishes the superiority of one of these techniques over the others, many thoracolumbar fractures treated with posterior surgical approaches have produced excellent results with minimal complications.23 Several authors have suggested that posterior distraction instrumentation and ligamentotaxis may yield clinical and radiographic results equivalent to those achieved after anterior or circumferential procedures in the setting of unstable burst injuries (Fig. 6).24-26 A posterior-only approach, however, may predispose individuals with severe vertebral body disruption or comminution to instrumentation failure and progressive loss of sagittal alignment.27,28 Alternatively, several authors have shown that anterioronly techniques are an effective treatment for burst frac-
197 tures29-33; these methods also have been successfully applied to thoracolumbar injuries involving the anterior and posterior vertebral elements.34 Anterior decompression may facilitate greater recovery of motor strength and bowel/bladder function than posterior indirect reduction strategies.30,35 Anterior procedures performed months or even years after the original injury have been found to improve pain and neurologic deficits associated with post-traumatic kyphosis, even in revision situations involving previous posterior surgery.4 In one of the few prospective, randomized studies comparing outcomes of acute thoracolumbar burst fractures after either an anterior or a posterior surgical approach, patients with stand-alone anterior constructs were noted to have fewer complications and were less likely to require reoperation.26 Anterior instrumentation systems also appear to maintain sagittal alignment better than short-segment posterior fixation methods.36 Other reports, however, have demonstrated no significant differences between anterior and posterior techniques in terms of neurologic status and clinical outcomes.37,38 Current data are inconclusive and only reveal the need for further investigation to determine which surgical strategy is best suited for a particular thoracolumbar fracture.
Summary and Conclusions
Figure 6 A lateral plain radiograph after an AP decompression and fusion for a symptomatic L3 burst fracture. A metallic static cage was used as an anterior strut graft filled with local autogenous bone graft. With the use of a supralamina hook at L2 and an infralaminar hook at L4, only 2 motion segments were immobilized. This is an example of short segment internal fixation.
Although the majority of thoracolumbar fractures may be treated nonoperatively, unstable injuries or those associated with neurologic deficits may benefit from surgical intervention. A posterior-only approach has become a well-accepted method for managing unstable thoracolumbar burst fractures with or without an associated neurologic deficit. The application of distractive forces to a posterior construct may indirectly reduce retropulsed fragments through ligamentotaxis and effectively improve the degree of canal occlusion. Anterior decompression and interbody fusion, either alone or in conjunction with posterior techniques, remain the preferred method of treatment for patients who present with incomplete neurologic deficits without any significant involvement of the posterior ligamentous complex. An unobstructed exposure of the thecal sac facilitates the safe and effective decompression of the spinal cord and nerve roots and provides the opportunity to reconstruct the anterior column with a strut graft or interbody device to restore normal sagittal alignment. By increasing the stability at the fracture site, anterior instrumentation may enhance the rate of successful arthrodesis and prevent the development of progressive posttraumatic kyphosis. In many clinical situations, the optimal surgical approach for a specific thoracolumbar fracture remains a matter of some controversy. Clinical cohort studies are certainly warranted at this time to establish a comprehensive operative protocol for these complex injuries.
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