Classification and Acute Management of Thoracolumbar Fractures

MANAGEMENT OF THORACOLUMBAR INSTABILITY

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CLASSIFICATION AND ACUTE MANAGEMENT OF THORACOLUMBAR FRACTURES Dennis G. Vollmer, MD, and Christopher Gegg, MD

Traumatic injuries of the thoracolumbar spine present with considerable heterogeneity in terms of causative mechanism, clinical presentation, and patterns of bone and soft-tissue injury. This broad clinical spectrum can present a dilemma regarding the optimal form of management. It is clear that successful results require treatment to be tailored to the specific type of injury. Recognition of various patterns of injury and the grouping of these into a coherent classification is critical to the development of a rational plan of management. Most classifications of thoracolumbar fractures are based primarily on reviews of plain radiographs and attempts to define the causative mechanisms of injury by extrapolation from the bony changes evident on the films. Implicit in this approach is the concept that an understanding of the forces involved in the creation of the injury will lead to correct conclusions as to the likelihood of instability and the proper mode of management. From a biomechanical point of view, all forces acting on the spine can be considered either as rotational or linear force vectors. Rotational forces include flexion and extension, lateral bending, and torsional forces. Linear force vectors include compression, distraction, and translational forces. These forces acting in isolation or, more commonly, in combination produce all known types of injury. Although

it is obvious that an infinite variety of combinations of these basic forces can exist, it is also obvious that specific patterns occur with some frequency. Although the concept of spinal stability is intuitive to most clinicians, the issue of defining instability in the clinical setting continues to present problems in the context of acute trauma, as discussed in this article, and in patients with congenital or degenerative abnormalities of the spine. White and Panjabi defined clinical instability as the inability of the spine under physiologic loads to maintain relationships between vertebrae such that there is neither acute nor subsequent neurologic injury, deformity, or pain.35In this definition, White and Panjabi recognized two overlapping manifestations of spinal instability. The first is acute instability,which is often apparent at or soon after the moment of injury, and the second is instability associated with delayed manifestations of pain, deformity, or, less commonly, neurologic deficit. In the context of thoracolumbar trauma, it is frequently the issue of delayed instability that presents the surgeon with the more difficult management questions, and it is in this context that many of the current classifications of thoracolumbar trauma were developed.', 33 Numerous schemes for the classification of injuries of the thoracolumbar spine have been

From the Division of Neurosurgery, University of Texas Health Science Center at San Antonio, San Antonio, Texas

NEUROSURGERY CLINICS OF NORTH AMERICA VOLUME 8 . NUMBER 4 OCTOBER 1997

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reported." Several reasons can be cited for the development of these schemes, including the definition of injury mechanisms, the separation into different levels of severity to allow evaluation of treatments, and morphologic classifications to define patterns of failure. Most classifications, however, represent an attempt to aid the clinician in determining the presence of instability and to define approhriate treatment. In 1938, Watson-Jones subdivided thoracolumbar fractures into three basic morphologic types.34These were the simple wedge fracture, the comminuted fracture, and the fracture dislocation. He also noted that iniuries were the result of flexion or extension forces and suggested that the former are best treated by extension casting. In 1949, Nicoll subdivided fractures into stable and unstable categories; the latter were associated with posterior ligament disr~ption.'~ Sir Frank Holdsworth is frequently recognized as one of the pioneers in the classification of thoracolumbar fractures with his papers outlining the two-column theory of spinal stability.16 Holdsworth examined patterns of bony injury and extrapolated them to probable injury mechanisms. He defined four primary types of injury forces: flexion, flexion-rotation, extension, and compression. Shear was later recognized as a fifth mechanism. Holdsworth further divided fractures into stable and unstable based on the division of the spine into an anterior and posterior column. Stability was primarily determined by the state of the posterior column. As a result of the Holdsworth scheme, burst fractures were considered stable injuries. Other investigators, such as Kelly and Whitesides19and Dewald; subsequently modified Holdsworth's concepts but retained the two-column formulation. In 1983, Francis Denis attempted to refine Holdsworth's observationswhen he presented the results of his retrospective review of over 400 thoracolumbar fracture^.^ As a result of his analysis, he was able to elaborate on Holdsworth's work and define a third, or middle, column of the spine. Presently Denis's threecolumn theory of the spine is probably the most widely accepted characterization. Denis defined the anterior column of the spine as the anterior vertebral body, the adja*References 4, 7-9, 12, 15, 16 ,18, 19, 21, 23, 25, 27, 29, and 34

cent annulus and disc, and the anterior longitudinal ligament. The middle column is comprised of the posterior aspect of the vertebral body, disc, and annulus and the posterior longitudinal ligament. The posteribr column is the neural arch and facets and the posterior ligamentous complex. Denis described four basic types of spinal injury (Table I), which were separable based on the patterns of failure exhibited. Stability in this scheme is based on the integrity of two of the three columns. Burst fractures were, therefore, considered unstable by this classification. Denis further subdivided each of the four basic injury patterns according to their morphology as apparent on radiographs. These subclassifications are reviewed in the sections regarding each main injury type. Concurrent with Denis's work. McAfee et a1 also developed a classification scheme of thoracolumbar fractures based on a review of 100 patients evaluated with computed tomogr a p h ~They . ~ ~ noted three primary modes of failure: axial compression, axial distraction, and translation. Six clinical fracture patterns were then described: wedge compression, stable burst. unstable burst. Chance fracture. flexion distraction, and translational fractures. Slightly different from Denis, McAfee distinguished between stable and unstable burst fracturesbased on the integrity of the posterior ligamentous ~omplex.'~ In 1984, Ferguson and Allen also developed a mode of classifying thoracolumbar fractures based on their clinical experiences treating pat i e n t ~ .This ~ , ~ svstem, ~ which thev termed a mechanistic clissification, identhed seven groups of injuries: compressive flexion, distractive flexion, lateral flexion, translation, torsional flexion, vertical compression, and distractive extension injuries. These investigators agreed with the Denis three-column concept but presented some differences in their interpretation of injury mechanisms and patterns of tissue failure. A specific area of departure was their characterization of burst fractures in which they believed that the middle column failed as the result of a hvdraulic blowout of the posterior vertebral wall, as a tension fracture: or a combination of the two. In 1989, Magerl et a1 proposed another classification of thoracolumbar fracture based on injury m~rphology.'~ Three primary injuring forces were described: compression, distraction, and rotation, and subtypes were then sep-I

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Table 1. THE FOUR MAJOR TYPES OF SPINAL INJURIES: MODES OF FAILURE Column TYpe

Anterior

Middle

Posterior

Compression Burst Flexion-distraction Fracture/dislocation

Compression Compression None or distraction Compression Rotation Shear

None Compression Distraction Distraction Rotation Shear

None or distraction (severe) None or splaying of pedicles Distraction Distraction Rotation Shear

From Denis F: The three-columnspine and its significance in the classification of acute thoracolumbar spinal injuries. Spine 8:817-831, 1983; with permission.

arated according to the severity of the fracture. Further subdivisions were indicated by numerical designations. McCormack et a1 developed what they termed a load sharing classification of spinal fractures in 1994.25This classification was the result of an analysis of fixation failures after treatment with transpedicular short-segment instrumentation. In this scheme, fractures are graded on a point system that addresses three aspects of the fracture, comminution of the body, apposition of the fracture fragments, and deformity correction (Fig. 1).This classification is designed to predict implant failure if short-segment fixation is employed and can aid the surgeon in deciding when to use an anterior load-bearing strut in the construct. Although there are many specific differences in the classifications cited above, there are also many similarities. In discussing classification of the specific injury subtypes, the authors will focus largely on the Denis classification because of its wide application, although it is acknowledged that many other schemes are equally valid and usable. Most surgeons would agree with a division of thoracolumbar fractures into wedge compression, burst, flexion distraction, and fracture dislocation subtypes.

pression fractures (Table 2): Type A has fracture of both end plates with separation of the anterior body, Type B has superior end plate fracture, Type C has fracture of the inferior end plates, and Type D constitutes lateral wedging of the body with or without concomitant ventral deformity or end plate involvement. In general, wedge compression fractures are stable injuries; however, severe degrees of compression can have associated posterior ligamentous failure in tension with rotation around the intact middle column. These injuries could, therefore, progress to severe kyphosis. This. latter type of injury should be suspected if splaying of spinous processes is observed on plain radiographs or if physical examination reveals significant interspinous tenderness or a palpable interspinous gap. Multilevel wedge compression fractures may also produce significant kyphotic deformity. Wedge compression fractures are often seen in the elderly and in others at risk for fracture because of osteoporosis or osteopenia. Occasionally, differentiation of benign from pathologic fractures can be an issue, although MR imaging may be helpful in distinguishing these entities. BURST FRACTURES

WEDGE COMPRESSION FRACTURES

Wedge compression fractures are the most common fracture pattern in the thoracolubar spine. These lesions are the result of failure of the anterior column in compression and occur after an axial load is applied in flexion. Significantly, the middle column is intact and, accordingly, there is no neurologic involvement. Denis described four subtypes of wedge com-

Burst fractures were initially described by Holdsworth who conceptualized the bursting of the vertebral body as the result of compressive forces being applied to the spine. He recognized the end plate fracture and surmised that the nucleus pulposus is driven into the vertebral body, which shatters with subsequent outward displacement of the bony fragm e n t ~ . Retropulsion '~ of bone into the canal produces the neurologic deficits seen in 50% or more of these patients. As stated above,

Little

More

Gross 3

Spread 2 Wide 3

Little

More

1

2

Most 3 Figure 1. Depiction of the load sharing classification. A, Comminution/ involvement: little (1) = < 30% comminution on sagittal reconstruction CT, more (2) = 30% to 60% comminution,and gross (3) = > 60% comminution. 6, Apposition of fragments: minimal (1) = minimal displacement of fragments on axial CT, spread (2) = at least 2 mm displacement of at least 50% of cross section of body, and wide (3) = at least 2 mm displacement of at least 50% of cross section of body. C, Deformity correction: 1 = kyphotic correction 5 3" on lateral plain films, 2 = kyphotic correction 4" to go, 3 = kyphotic correction 2 10". Fractures with scores of 6 or less are suitable for treatment with posterior short-segment transpedicular fixation. Fractures with scores of 7 or more generally require more extensive stabilization (e.g., incorporation of an anterior load-bearing construct.) (From McCormick T, Kavaikovic E, Gaines RW: The load sharing classification of spine fractures. Spine 19:1741-1744, 1994; with permission.)

CLASSIFICATION AND ACUTE MANAGEMENT OF THORACOLUMBAR FRACTURES

Table 2. CLASSIFICATION OF WEDGE COMPRESSION FRACTURES

Tv~e A ~;~B e Type C Type D

Fracture of both end dates Superior end plate fracture Inferior end plate fracture Lateral wedging

From Denis F: The three-column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine 8:817-831, 1983; with permission.

however, Holdsworth considered these fractures to be stable because of preservation of the posterior elements. Denis described the radiographic findings associated with burst fractures, including the fracture of one or both end plates, the disruption of the posterior vertebral cortex with retropulsion of bone, the widening of the interpedicle distance, the green stick fracture of the lamina, the loss of body height, and angular deformity. Noting that the hallmark of all burst fractures is the failure of the middle column in compression, Denis subdivided burst fractures into five categories (Table 3). Type A fractures have fracture of the end plates. Type B fractures have fracture of the superior end plate with retropulsion of the posterosuperior corner of the body into the canal. The Type C fracture has fracture of the interior end plate with retropulsion of the posteroinferior body into the canal. Type D fractures are burst fractures with a rotatory component in the axial plane. Type E fractures are burst fractures with lateral flexion. According to the three-column concept of Denis, burst fractures are considered unstable because, by definition, they have disruption of two columns. To account for the presence of stable burst fractures, McAfee suggested that middle-column failure in compression was stable unless posterior-column injury had also occurred.23In their load-sharing classification mentioned above, McCormack et a1 have also attempted to better define the need for operative intervention for burst fractures. Farcy and Wiedenbaum likewise studied the need for operative stabilization in thoracolumbar burst fractures and developed the sagittal index, a measure of kyphotic angulation corrected for normal sagittal contour.ll In a cadaver study of burst fractures, Panjabi et a1 demonstrated acute instability in multiple planes.28There remains considerable controversy regarding optimal treatment of burst fractures, some of which are revisited in other articles of this is-

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sue. There are cogent arguments for nonoperative treatment and posterior and anterior surg-ical stabilization with or without direct canal " decompre~sion.~,'~, 17,31,32 It seems probable that each approach has its optimal application in the context of burst fractures. Clinicians are hopeful that a classification will be developed that allows appropriate case selection, FLEXION DISTRACTION INJURIES

These injuries are characterized by the failure of all elements in tension. The classic example of this injury is the Chance or seat-belt type injury in which tension failure of all three columns occurs through the bone. Alternatively, flexion distraction injuries can produce failure entirely through the ligamentous structures or may combine bony and ligamentous injuries. The radiographic hallmark of these injuries is the lengthening of the affected segment as a result of the distractive force. A translational component may also be present in these injuries, although the predominant deforming forces are distractive. Denis, in his classification, separated Chance-type fractures from flexion distraction injuries citing a lack of dislocation in the former. The latter were included as a subtype of fracture dislocation.

Table 3. BURST FRACTURES

Types A, B, and C are mainly diagnosed on lateral radiographic views: Type A Fracture of both end plates, seen in the low lumbar region. Its mechanism is pure axial load Type B Fracture of the superior end plate. This is the most frequent burst fracture. It is seen at the thoracolumbar junction. The mechanism of injury is axial load and flexion. Type C Fracture of the inferior end plate. This fracture is rare. The mechanism of injury also appears to be axial load and flexion. Type D Burst rotation. This is typically a midlumbar fracture, which could be diagnosed as a fracture-dislocation. The mechanism of injury is axial load and rotation. Type E Burst lateral flexion. This fracture results from axial load and lateral flexion. It differs from the lateral compression fracture in that the posterior wall of the vertebral body fractures, allowing retropulsion of bone back into the canal. From Denis F: The three-column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine 8:817-831, 1983; with permission.

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Gertzbein and Court-Brown also offered a classification of these fractures based on three aspects: the location of the posterior fracture, the location of the anterior fracture, and the status of the vertebral body.12,l3 According to Denis, however, flexiondistraction injuries could be subdivided into four types based on failure patterns (Table 4). Type A is the classic Chance fracture with failure confined to the bone, affecting one segment. Type B is failure through ligament only affecting one level. Types C and D are injuries with bony and ligamentous failure. Type C injuries have failure through bone at the level of the middle column, and Type D injuries have failure through ligament (disc) at the level of the middle column. FRACTURE DISLOCATIONS

Fracture dislocations are complex injuries with failure of all three columns. These injuries are unstable by any definition and are the result of multiple forces. Denis also categorized fracture dislocations into six types (Table 5). Type A is the "slice fracture" in which there is rotational shear through the body. Type B is the result of similar torsional forces, but failure is through the disc anteriorly. Type C is a translational shear injury in which the shearing forces are in the posteroanterior direction, and the superior body is anteriorly translated with fracture of the facets. The failure anteriorly involves the disc and the anterior and posterior longitudinal ligaments. The Denis type D injury is the result of similar mechanisms as the Type C except that the neural arch is fractured and left posteriorly as a "floating lamina." Type E fractures are the result of an anteroposterior translational force in which most of the failure is through the ligamentous structures. Finally, the Type F injury is a threeTable 4. SEAT-BELT TYPE INJURIES: FLEXION DISTRACTION INJURIES Type A Type B Type C Type D

One level, through bone (Chance fracture) One level, through the ligaments Two level through bone at the level of the middle column Two level through ligaments at the level of the middle column

From Denis F: The three-column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine 8:817-831, 1983; with permission.

Table 5. FRACTURE DISLOCATIONS Type A Type B Type C

Type D Type E

Type F

Flexion rotation through the vertebral body "slice fracture" Flexion rotation through the disc. It is accompanied by unilateral fracture of the superior articular process Posteroanterior shear injury. Intact anterior vertebral bodies, fracture of the superior articular facet, which has been sheared off by the anterior. The spinous process or entire posterior arch may be fractured by the same mechanism. Posteroanterior shear injury in which a large part of the posterior arch may be left behind (floating lamina) Anteroposterior shear injury. The posterior arches and anterior vertebral bodies may be entirely intact, but the three ligamentous columns are disrupted Flexion distraction. The posterior, middle, and anterior ligamentous columns are disrupted but for the anterior longitudinal ligament, which strips off the vertebral body below (compare with seat-belt injuries).

From Denis F: The three-column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine 8:817-831, 1983; with permission.

column injury in which flexion-distraction forces disrupt all of the ligamentswith anterior rotation and translation of the superior body, which is often tethered only by the anterior longitudinal ligament. MISCELLANEOUS INJURY PATTERNS

A variety of other minor fractures may be collected under this heading. These include isolated transverse process fractures, spinous process fractures, and facet or laminar fractures. Bipedicular fractures and acute fractures of the pars interarticularis may also be included here. ACUTE MANAGEMENT OF THORACOLUMBAR INJURIES

Early management of individuals suspected of having a thoracolumbar injury follows the basic principles of trauma management. Patients who sustain acute thoracolumbar injuries typically have been subjected to high energy forces. Common mechanisms of injury include vehicular trauma (both passenger and pedestrian), industrial accidents, and falls

CLASSIFICATION AND ACUTE MANAGEMENT OF THORACOLUMBAR FRACTURES

from a height. Likewise, patients with penetrating injuries, such as gunshot wounds, may sustain injury to the thoracolumbar spine and neural elements. These patients are at risk for multisystem injuries and should be thoroughly evaluated, optimally by a multidisciplinary team. Life-threatening injuries often seen in association with high-energy thoracolumbar trauma include severe closed-head injuries, thoracic great vessel injury, and blunt chest trauma including cardiac contusion. These sorts of injuries take precedence over the spine injury, although their assessment and treatment must not compromise neurologic function. Patients are initially kept immobilized on a spine board with a rigid cervical orthosis as appropriate. After the acute issues of airway, breathing, and circulation have been addressed, cervical radiographs are obtained, and the neurologic status of the patient is determined and carefully documented to establish a baseline. It is axiomatic that neurologic assessment include quantitative evaluation of motor function, sensory testing to include sacral dermatomes, and an examination of sphincter function. Dorsal column and ventral cord function should be assessed. Serial examinations are performed to allow detection of deterioration during the course of acute management. The patient is also examined for evidence of gross spinal deformity, tenderness, and muscle spasm. The back should be inspected and palpated at some point to look for contusions, abrasions, or lacerations that may require specific treatment. Additionally, palpation of the spinous processes may reveal an interspinous gap or focal interspinous tenderness, both of which may indicate posterior ligamentous disruption. At the authors' institution, this portion of the examination is performed after assessment of plain radiographs of the spine. Plain radiographs of the entire spine should be obtained in the lateral and anteroposterior projection. The frequency of noncontiguous fractures of the spine may be more than IOO/O.~ For this reason, when a fracture is detected, even greater vigilance in evaluating the remainder of the spine is required. The fact that the thoracolumbar junction may be off the film or poorly visualized on plain chest radiographs and lumbar spine films also requires close attention. If a neurologic deficit of spinal cord or cauda equina origin is determined, the patient is

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given an intravenousbolus of methylprednisolone sodium succinate (MPSS) (50 mg/kg) over 15 minutes and started on an infusion as described by Bracken et a1 (5.4 mg/kg/hr for 23 hour^).^ This regimen is not given, however, if the patient is more than 8 hours from the time of injury because MPSS has not been shown to be helpful in decreasing the effects of injury after this interval. In contrast to patients with cervical cord injuries, patients who have neurologic deficits from injury at the thoracolumbar level generally do not exhibit acute hemodynamic or respiratory difficulties in the absence of other injuries. Nonetheless, when present, hypotension may exacerbate spinal cord injuries and, therefore, should be corrected with volume replacement and pressors if necessary. Computed tomography (CT) is routinely performed when thoracolumbar fractures are detected. CT allows much more complete examination of the middle column and the status of the posterior elements, especially the facets. It is desirable to scan at least one full normal segment above and below the level of fracture. If surgical intervention is anticipated, the entire segment to be instrumented is scanned. This is particularly helpful when transpedicular fixation is to be used. Certain fractures or dislocationsmay not be visualized well by routine axial scanning techniques (e.g., Chance fractures and distraction injuries). In this situation, thin-cut CT or sagittal reconstruction may be helpful. Although CT reliably detects canal compromise as the result of bony impingement, disc herniation and epidural hematoma may be easily missed. In some circumstances, CT with intrathecal contrast is still used to vrovide better definition of the status of the neural elements. Most centers, however, presently use MR imaging to resolve these questions. MR imaging is routinely performed on patients with neurologic deficit and when additional information regarding disc herniation, dural tear, or ligamentous injury is sought.3*26 Imaging with MR is often very helpful in demonstrating ligamentous disruption and allowing visualization of the spinal cord, conus, and cauda equina. Signal change within the cord on T2-weighted images provides anatomic documentation of injuries suggested by neurologic deficits. Visualization of the level of the conus may also be helpful in preoperative planning and the assessment of the need for

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decompression. Disadvantages to the use of MR imaging in the acute evaluation of trauma patients include the relative inaccessibility of the patient in the bore of the scanner, the potential problems associated with monitoring and ventilatory support in the MR imaging environment, the relatively long scanning times required for MR imaging compared with CT, and the availability of the MR image scanner in some hospitals. Nonetheless, the use of MR imaging for the evaluation of some of these patients is increasingly recognized. Following performance of the appropriate radiologic assessment, a therapeutic decision is made based on the fracture diagnosis, the results of the neurologic examination, and the medical condition of the patient. The issues of operative versus nonoperative management and various surgical approaches are addressed elsewhere in this issue. When surgical treatment is selected, however, the issue of timing of surgery is raised. Thoracolumbar fractures are rarely treated as an emergency. The potential for significant blood loss and long times under anesthesia with these fractures may be a relative contraindication for operating on hemodynamically unstable or only marginally stable patients. Possible indications for emergency operation would include progressive neurologic deterioration or significant epidural hematoma with cord or cauda equina compression. Most operative treatment is carried out on an urgent elective basis at the first opportunity. Associated injuries and other comorbidity may dictate postponement of the operative procedure. There is some evidence that early operative results in terms of restoration of sagittal alignment and canal clearance are superior.30Conversely, some authors believe that the risk for neurologic deterioration may be higher in early surgery for spinal instabilit~.~~ After the acute evaluation of these patients is complete, it is a priority to remove the backboard as soon as possible. Failure to do so can result in considerable problems with skin breakdown especially in patients with paraplegia. Because ileus is generally present in the acute period after a thoracolumbar fracture, a nasogastric tube is placed. Prophylaxis against gastroduodenal ulceration should be employed in patients not receiving enteral feedings. Hypovolemia is corrected as appropriate and maintenance IV fluids are administered.

A Foley catheter is generally employed in the acute phase to allow close monitoring of fluid balance. Symptomatic anemia is corrected with transfusion as appropriate. Prophylaxis for deep venous thrombosis should be begun early and includes pneumatic compression hose. Paraplegic patients with normal coagulation status are also given subcutaneous minidose heparin. Frequent patient repositioning is performed to prevent decubiti. Severe instability that precludes log-rolling may warrant a special mechanical bed or may be an indication for earlier surgery.

CONCLUSIONS

The development of classification systems for thoracolumbar fractures is a natural consequence of the efforts to optimize treatment of these challenging injuries. Like the treatments themselves, the classification continues to evolve. As our understanding of prognostic factors improves and our ability to better visualize the anatomy of the injury is enhanced, injuries will be classified in ways which will better direct the appropriate course of management. It is likely that future classifications will combine information from the pattern of softtissue injury, bony injury, and neurologic examination and include any comorbidities. When this goal can be achieved, the comparison of different treatments will be more straightforward and our development of prognostic tools will be enhanced. It is evident that the major determinants of outcome from thoracolumbar trauma occur at the moment of injury. Nonetheless, the acute stage of treatment can significantly influence the patient's course of recovery and ultimate functional result. Attention to detail is required to minimize complications and improve our surgical results.

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CLASSIFICATION AND ACUTE MANAGEMENT OF THORACOLUMBAR FRACTURES

3. Brightman RP, Miller CA, Rea GI, et al: Magnetic resonance imaging of trauma to the thoracic and lumbar spine: The importance of the posterior longitudinal ligament. Spine 17541-550, 1992 4. Bucholz RW, Gill K: Classification of injuries to the thoracolumbar spine. Orthop Clin North Am 176773, 1986 5. Calenoff L, Cessare JW, Rogers LF, et al: Multiple level spinal injuries: Importance of early recognition. AJR 130:665-699,1978 6. 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 7. Denis F: The three-column spine and its significance in the classification of acute thoracolumbar spinal injuries. Spine 8:817-831, 1983 8. Dewald R: Burst fractures of the thoracic and lumbar spine. Clin Orthop 189:150, 1984 9. Ferguson RL, Allen BL Jr: A mechanistic classification of thoracolumbar spine fractures. Clin Orthop 189:7788, 1984 10. Ferguson RL, Allen BL Jr: An algorithm for the treatment of unstable thoracolumbar fractures. Orthop Clin North Am 17105-112,1986 11. Farcy JPC, Weidenbaum M, Glassman SD: Sagittal index in management of thoracolumbar burst fractures. Spine 15:958-965, 1990 12. Gertzbein SD, Court-Brown CM: Flexion-distraction injuries of the lumbar spine: Mechanisms of injury and classification. Clin Orthop 227:52-60, 1988 13. Gertzbein SD, Court-Brown CM: Rationale for the management of flexion-distraction injuries of the thoracolumbar spine based on a new classification. J Spinal Disord 2:176-183,1989 14. Haid RW, Kopitnik: Thoracic fractures: Classification and the relevance of instrumentation. In Saul TG (ed): Clinical Neurosurgery. Baltimore, Williams and Wilkins, 1992, p 213 15. Harms J: Classification of fractures of the thoracic and lumbar vertebrae. Fortschr Med 105:545-548, 1987 16. Holdsworth FW: Fractures, dislocations and fracturedislocations of the spine. J Bone Joint Surg (Br) 45:620, 1963 17. Jodoin A, Dupuis P, Fraser M, et al: Unstable fractures of the thoracolumbar spine: A 10-year experience at Sacre-Coeur Hospital. J Trauma 25:197-202, 1985 18. Kazarian L: Injuries to the human spinal column: Biomechanics and injury classification. Exerc Sport Sci Rev 9:297-352, 1981 19. Kelly RP, Whitesides TE Jr: Treatment of lumbardorsal fracture-dislocation. Ann Surg 167705, 1968

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20. Lin RM, Panjabi MM, Oxland TR: Functional radiographs of acute thoracolumbar burst fractures. Spine 18:1431-1437,1993 21. Magerl F, Harms H, Gertzbein S, et al: Classification of spinal fractures. Presented at the meeting of the American Academy of Orthopaedic Surgeons, Vail, Colorado, 1989 22. Marshall LF, Knowlton S, Garfin SR, et al: Deterioration following spinal cord injury: A multicenter study. J Neurosurg 66:400-404, 1987 23. McAfee PC, Yuan HA, Fredrickson BE, et al: The value of computed tomography in the thoracolumbar fractures: An analysis of one hundred consecutive cases and a new classification. J Bone Joint Surg 65:461473, 1983 24. McAfee PC, Yuan HA, Lasda NA: The unstable burst fracture. Spine 7:365-373, 1982 25. McCormack T, Karaikovic E, Gaines RW. The load sharing classification of spine fractures. Spine 19:17411744, 1994 26. Modic MT, Hardy RW, Weinstein MA, et al: Nuclear magnetic resonance of the spine: Clinical potential and limitation. Neurosurgery 15:583-592, 1984 27. Nicoll EA: Fractures of the dorso-lumbar spine. J Bone Joint Surg (Br) 31:376-394, 1949 28. Panjabi MM, Oxland TR, Lin RM, et al: Thoracolumbar burst fracture: A bio-mechanical investigation of its multidirectional flexibility. Spine 19:578-585, 1994 29. Parrini L, Cabitza P, Verdoia C, et al: Vertebral fractures: Classification, pathological and radiographic anatomy, radiographic diagnosis. Ital J Orthop Traumat01 9:5-20, 1983 30. Schlegel J, Bayley J, Juan H, et al: Timing of surgical decompression and fixation of acute spinal fractures. J Orthop Trauma 10:323-330, 1996 31. Schnee CL, Ansell LV: Selection criteria and outcome of operative approaches for thoracolumbar burst fractures with and without neurological deficit. J Neurosurg 86:48-55, 1997 32. Singer BR: The functional prognosis of thoracolumbar vertebrae fractures without neurological deficit: A long-term follow-up study of British Army personnel. Injury 26:519-521, 1995 33. Speth MJGM, Oner FC, Kadic MACC, et al: Recurrent kyphosis after posterior stabilization of thoracolumbar fractures. Acta Orthop Scand 66:406-410,1995 34. Watson-Jones R: The results of postural reduction of fractures of the spine. J Bone Joint Surg (Am) 20:567586, 1938 35. White AA 111, Panjabi MM: Clinical biomechanics of the Spine. Philadelphia, JB Lippincott, 1978, p 240 36. Willen JAG, Gaekwad UH, Kakulas BA: General orthopaedics: Acute burst fractures. Clin Orthop 276:169-175,1992

Address reprint requests to Dennis G. Vollmer, MD Department of Neurosurgery The University of Texas Health Science Center at San Antonio 7703 Floyd Curl Dr. San Antonio, TX 78284-7843