Anatomy

The vertebral column provides humans with the ability to maintain an upright posture, protects the neural and visceral organs (i.e., heart, lungs, abdominal contents), and helps with motility. It consists of 29 vertebrae arranged in 4 major curves, 2 primary curves (thoracic and sacral), and 2 compensatory or secondary curves (cervical and lumbar).⁹ The vertebral column also provides a protective environment for the spinal cord and neural elements. The vertebral body, pedicles, and dorsal elements surround the spinal cord, permitting the spinal nerves to exit through the paired neural foramina. The laminae are formed as dorsomedial extensions of the pedicles and fuse in the midline to create the spinous processes (Fig. 66-1). Nomenclature for the thoracic spine varies; however, in this chapter the thoracic spine is considered to span T1 through T10, and the thoracolumbar junction T11 through L2.

FIGURE 66-1 Axial CT image of L2 vertebral body identifying the dorsal elements.

Primary spinal curves are present at birth, are maintained through life, and are relatively rigid or stiff. Secondary curves are more flexible and result from development or adaptation. The first secondary curve is the development of cervical lordosis at approximately 3 to 9 months of age as the infant begins supporting his or her head and sitting upright. The lumbar lordosis develops later (between 12 and 18 months), as the child begins to ambulate and assumes an upright posture.⁹ A thorough knowledge of the thoracic spine and thoracolumbar junction anatomy facilitates a greater understanding of the biomechanical, radiographic, and surgical techniques that are used to treat these fractures.

Thoracic Spine

The thoracic spine differs from the cervical and lumbosacral spines as a result of its articulation with the rib cage (T1-12), extensive ligamentous support network, coronal facet joint orientation, and small spinal canal-to-neural element ratio (Fig. 66-2). The thoracic laminae increase in width and thickness from T1 to T12, and this prevents hyperextension.¹⁰ The anterior longitudinal ligament (ALL) provides further stability by increasing the tensile strength from T1 to T12. Moreover, the dorsal, ventral, and lateral diameters of the vertebral bodies increase from T2 to T12.^11–15 The thoracic kyphotic curve results from the greater height of the dorsal vertebral wall as opposed to the ventral vertebral wall. The transverse pedicle diameters decrease from 9 mm at T1 to 5 mm at T5 and then increase in size distally to T12.¹⁴ In the sagittal plane, pedicle width increases from T1 to T11. However, in the transverse or axial plane, the thoracic vertebrae have a triangular configuration and appear heart shaped. There is significant variability in what is considered the “normal” sagittal curvature of the thoracic spine. This value has been reported to be between 20 and 45 degrees,^13,16,17 with each individual vertebral body contributing approximately 3.8 to 3.9 degrees of kyphosis through its wedged-shaped angulation. This variability is further influenced by age (increases with age) and sex; women have a greater degree of kyphosis than men.^16,17 There is also a significant degree of variability on a segmental basis, particularly at the transitional regions with the lordotic cervical and lumbar spines.^12,18,19 The apex of thoracic kyphosis is typically located at the seventh thoracic vertebra, but varies with each individual. The thoracic spine typically has a mild, right-sided lateral curvature.^9,17 The etiology of the right-sided lateral curve is debated but is believed to be either the result of hand dominance (right-hand majority) or created by pulsations of the thoracic aorta.⁹

FIGURE 66-2 Axial CT image of T6 vertebral body identifying the relationship between the vertebral body and the rib head’s articulations.

The thoracic pedicles are situated toward the rostral portion of the vertebral body, close to the superior disc space (Fig. 66-3). The pedicle angle decreases from T1 to T12; it is 251 degrees at T1 and 0 degrees at T12.^11,17,20 The pedicle location on the vertebral body progressively migrates as the spine is descended in a caudal direction. The medial pedicle cortical wall is approximately two to three times thicker than the lateral wall.²¹

FIGURE 66-3 Sagittal CT reformatted image of T2 and T3 vertebral bodies illustrating the relationship of the pedicle to the intervertebral disc space in the thoracic spine.

The thoracic transverse processes project laterally from the dorsal articular pillars and decrease in length caudally.⁵ However, unlike the lumbar spine, the relationship between the transverse process and the midpoint of the pedicle is not as clearly defined. McCormick²² showed that there is a significant degree of variability in the relationship of the transverse processes to the pedicles. The midpoint of the T1 transverse process is approximately 5 mm rostral to the center of the pedicle, whereas at T12 the transverse process-to-pedicle relationship changes to approximately 6 mm caudal.²⁰ Comparatively, this transverse process to pedicle relationship is greater than 1 cm at both T1 and T2, and is approximately 0 cm when one analyzes T6 and T7.²⁰

The thoracic spine facet articulations are considered apophyseal joints and are composed of a ligamentous capsule with a synovial lining. These ligaments in the thoracic spine are thicker than their cervical counterparts. In the thoracic spine, the costovertebral (rib-vertebra) facets are located anterior to the transverse processes. The isthmus of bone between each pair of superior and inferior facets is called the pars interarticularis, a site of fracture and bony nonunion for those with a condition known as spondylolysis. The joints are located at the rostral and caudal borders of the laminae and situated medial to the transverse processes (Fig. 66-4). The caudal facet’s ventral surface articulates with the rostral facet’s dorsal surface. Thoracic facet joints are oriented in a coronal plane and therefore limit the degree of flexion and extension of the thoracic spine.²³

FIGURE 66-4 T12 burst fracture sustained after a motor vehicle accident. Note the high definition of the posterior displaced fragment (A, arrow), along with the vertebral body sagittal fracture (B, arrow) and the associated laminae fractures.

There are several key anatomic features that are essential for understanding the relationship of the ribs and the thoracic vertebrae. First, the ribs articulate with the thoracic vertebrae at two separate locations. The head of the rib articulates with the transverse process of the body at the costotransverse articulation, except at T1, T11, and T12. This articulation is supported with a large superior costotransverse ligament, which connects the rostral rib segment to the caudal transverse process (see Fig. 66-2). It also articulates with the disc space adjacent to the body above by virtue of the rib head of the same-numbered vertebral body articulating with it through the two costal hemifacets (T2-10).

The strong ligamentous structures that compose the costovertebral joint make the thoracic disc the strongest of all the vertebral discs.²⁴ The superior hemifacet (rostral on the vertebral body and caudal to the rib) is located over the pedicle, such that the sixth rib articulates with the fifth and sixth thoracic vertebral bodies and overlies the sixth vertebral pedicle. Because of the rostral location of the thoracic pedicle on the vertebral body, the sixth rib overlies the T5 to T6 disc space. Understanding the anatomic relationship of the rib head with the pedicle allows the surgeon to remove the rib head and identify the neurovascular bundle, along with the neural foramina and thecal sac, at that level.

The spinal canal diameter varies throughout the vertebral column and is the narrowest in the midthoracic region (T3-9).^11,13,25 The transverse spinal canal diameter decreases from T1 to T3 and then increases caudally into the lumbar region. The anteroposterior (AP) diameter, however, is more varied.^13,25 Therefore, in the thoracic region a minor degree of canal encroachment can compromise the narrow canal and may result in neurologic compromise.^26,27 Furthermore, the thoracic spinal cord has the most tenuous blood supply.¹³ Thus, small canal size, limited blood supply, and the high degree of energy required to create a thoracic fracture combine to result in a 90% incidence of neurologic deficit in patients who sustain a thoracic fracture.²⁸

Imaging

It is not uncommon in clinically unstable trauma patients for fractures not to be identified early in the resuscitative period. It has been reported that between 5% and 15% of multisystem trauma patients have occult fractures not diagnosed on their initial evaluation.^31–33 Although thoracic vertebral fractures make up only a minor proportion of traumatic fractures, they are extremely difficult to visualize compared with other vertebral or appendicular fractures. Approximately 20% to 50% of superior thoracic spine fractures are not diagnosed on admission plain radiographs.^5,34,35 Therefore, all suspected spine trauma patients should be immobilized on admission until a thorough and detailed spinal evaluation can be performed. If appropriate stabilization precautions are not taken in this patient population, unforeseen neurologic compromise may result.⁶

Initial radiographic assessment includes AP and lateral spine films. The AP film should be examined for loss of vertical body height, fracture of the oval-shaped pedicles, increased interpedicular distance, transverse process or rib fractures, and malalignment of vertebral bodies or spinous processes without a history of scoliosis. The lateral radiograph should be examined for loss of body height, disruption of the rostral or caudal end plate, dorsal cortical wall fracture with retropulsed bone, fracture of spinous processes, widening of interspinous distance, and subluxation or angulation of vertebral bodies.³⁶ Malalignment in any plane, but especially in the AP plane, suggests the possibility of a fracture-dislocation.¹² Plain radiographs may not be accurate in determining the involvement of the posterior vertebral wall with a thoracic fracture.^37,38

Plain radiographs are particularly useful in assessing the patient’s overall sagittal and coronal balance. If a deformity exists, a useful radiographic technique to determine the degree of deformity is measurement of the Cobb angle, which is the subtended angle measured between a perpendicular line drawn from the superior end plate of the vertebral body above the injured vertebral body and the inferior end plate one level below the injured body (see Fig. 66-20). This method of measuring spinal sagittal angulation has been shown to have the highest degree of intraobserver and interobserver reliability.³⁹

In the presence of a vertebral body injury, the entire spine should be imaged in an orthogonal manner because of the high incidence (5–20%) of noncontiguous spine fractures.^40–42 The rostral thoracic spine can be difficult to visualize on lateral plain radiographs because of the patient’s shoulders and body habitus, and a swimmer’s view may provide better visualization of the cervicothoracic junction down to the T3 vertebral body.⁴³ Radiographically, a typical superior end-plate thoracic fracture shows loss of vertebral height, with or without malalignment, a widened paraspinal line, and possibly a widened mediastinum.³⁵ Because of difficulties in imaging the upper thoracic region (T1-4), a high index of suspicion is required on the physician’s part to avoid missing injuries at this level. The physician should have a low threshold for ordering supplemental imaging modalities to assist in the diagnosis, such as CT and MRI.

Magnetic Resonance Imaging

MRI has further improved the ability to visualize and comprehend the pathoanatomy of soft tissues, ligaments, and intervertebral discs, and the neural element disruption that occurs after spine injury. Unfortunately, MRI is not always available because of its expense, because it takes longer to implement, and because it cannot be performed on patients with ferromagnetic implants. Today it has supplanted CT myelography as the imaging tool of choice for the neuraxis because it is faster and noninvasive and allows improved visualization of the spinal cord parenchyma.⁵³ MRI provides the physician with the ability to identify edema and/or hemorrhage of the spinal cord⁵³ (Fig. 66-5). These images have been correlated with neurologic outcomes, where the presence of hemorrhage in the spinal cord parenchyma is associated with minimal neurologic recovery.⁵⁴

FIGURE 66-5 T2-weighted MRI of cervical spine of C5 ASIA type A spinal cord–injured patient after an automobile crash. Note severe intraparenchymal edema, along with hemorrhage in the spinal cord.

MRI evaluation is especially useful at the thoracolumbar junction because of the variable location of the cauda equina and conus medullaris in the adult population at this level.⁵⁵ A neurologic examination can be difficult to interpret at the conus-cauda equina transition level as a result of the presence of lumbar spinal nerve sparing, the presence of concurrent injuries, sedation, or indwelling catheters, and delayed reflex recovery (Fig. 66-6). Accurate neural visualization may help in clarifying the pathoanatomy in these clinical situations.

FIGURE 66-6 T12 burst fracture with retropulsion of fragment into canal. Note that the fragment is compressing the conus medullaris (arrow) and there is resulting spinal cord edema. Clinically the patient has a severe lower extremity paresis and loss of bowel and bladder function.

Biomechanics

The vertebral body is the primary load-bearing structure of the spine, with the intervertebral disc transferring all forces applied to the adjacent vertebral bodies.^56,57 The anulus fibrosus of the intervertebral disc supports a significant portion of all applied axial and lateral loads and resists tension and shearing.⁵⁸

The spinal ligamentous structures are essential in maintaining overall sagittal balance. The posterior longitudinal ligament (PLL) is a relatively weak ligament that provides some restriction to hyperflexion, along with the ligamentum flavum. The thicker ALL functions in resisting spinal hyperextension and distraction.⁵⁹ This thick ligament has fatigue loading values that are approximately double those of any other spinal ligaments,^57–59 and its strength increases caudally from C3 to the sacrum.⁵⁹ The intrinsic strength of the spinal ligaments is only an isolated factor in the overall stability of the spinal column. The lever arm by which these ligaments act on the spine also significantly affects the overall stability of the vertebral column (Fig. 66-7).

FIGURE 66-7 The lever arm of the ligaments to the instantaneous axis of rotation (IAR) greatly influences the stability of the spine. The weaker interspinous ligaments (ISL) work at the greatest distance from the IAR and therefore provide significant resistance to gravitational influences. ALL, anterior longitudinal ligament; LFL, ligamentum flavum; PLL, posterior longitudinal ligament.

Abnormal motion patterns and coupling can be an indication of clinical instability, which ultimately must be treated in some manner. Clinical instability can be quantitatively measured in respect to the moving segment’s instantaneous axis of rotation (IAR). The IAR is an axis about which a vertebra rotates at some instant of time.⁴⁶ This axis is a geometric concept and does not apply to a specific anatomic location.⁶⁰ However, in the normal thoracic and thoracolumbar spine, the IAR is located in the ventral vertebral body. For normal spinal units, the IAR for each of the rotary modes (flexion, extension, lateral bending, and axial torsion) is confined to a relatively small area somewhere within the spinal unit.¹⁴ The facet capsules are very strong ligaments and act with a short lever arm by their relationship to the IAR, whereas the intraspinous ligaments are relatively weak but act with a great lever arm because of their increased distance from the IAR. Based on the ligaments’ relative strengths, it would seem that the intraspinous ligaments are not important, but both ligaments significantly affect the strength and structure of the spine.

The thoracic spine differs from the remainder of the spinal column because it is supported by and maintains articulations with the ribs (see Fig. 66-2). The intact rib cage increases the axial load-resisting capacity of the thoracic spine by a magnitude of four. The rib cage and facet articulations limit rotation, and therefore most thoracic spine fractures occur from a flexion or axial compression force vector.⁶¹ The majority of stability in flexion is provided by the costovertebral articulations.⁶² A significant factor in the degree and extent of fracture character is the rate of force impact loading.⁶³

Gravitational forces exert a significant axial load on the vertebral column in the standing adult human. The center of gravity of the body, located where all forces are counterbalanced such that there is no net movement, is approximately 4 cm anterior to the first sacral vertebra.¹⁴ This results in a ventral bending (angular) vector acting on the spinal column. This bending force draws or attracts the ventral spinal column closer to the center of gravity such that a lower energy state may be achieved by the paraspinous musculature. The dorsal ligamentous complex and dorsal paraspinal musculature, acting as a tension band, counteracts these forces, such that the net sum of the vectors acting on the spine equals zero. Therefore the dorsal ligamentous, osseous, and muscular components are essential for overall support of the spine to prevent a change in the spine’s sagittal alignment. Trauma resulting in disruption of the spinal ligaments or osseous structures may change the net vector sum from zero, resulting in the potential for spinal imbalance. These new vectors acting on the spine, if not corrected, may result in a gradual spinal deformity with or without associated pain or neurologic deterioration. Whiteside used the analogy of a construction crane to illustrate this mechanical principle⁶⁴ (Fig. 66-8). In this analogy, the weight to be lifted is ventral to the crane, where the boom (anterior vertebral column) is under compression and the guidewires (posterior columns) are under tension. Failure of either supporting structure independent of the other will result in mechanical failure or collapse.

FIGURE 66-8 A and B, Whiteside’s crane analogue of the spine illustrates the delicate equilibrium of the anterior compression vectors against the posterior tension vectors.

(Copyright Cleveland Clinic Foundation.)

The thoracic and thoracolumbar vertebrae are at increased risk for development of compression fractures after trauma as a consequence of axial loads resulting from the natural kyphotic curvature of the thoracic spine.⁶⁵ The kyphotic posture results in the placement of axial forces on the ventral portion of the vertebral body. An axial load causes all points that are ventral to the IAR of the spine to come closer together while simultaneously all points that are dorsal are spread apart. Therefore, if the strength of the ventral vertebral body is exceeded, a fracture of the vertebral body occurs, resulting in a vertebral compression fracture (VCF). The traumatic forces may also exceed the strength of the dorsal vertebral body and ligamentous elements, resulting in disruption of the dorsal tension band. The destruction of the ventral vertebral stabilizing elements (i.e., vertebral body, disc, ligaments, anulus) causes the IAR to migrate dorsally to the region with intact supporting structures.^65,66 Dorsal migration of the IAR causes the previous mechanical advantage of a longer level arm from which the dorsal ligaments and muscles acted to be shortened. This migration of the IAR also simultaneously increases the distance of the center of gravity to the IAR, thereby placing further distraction on the dorsal spinal column and compression on the ventral spinal column^65,66 (see Fig. 66-7).

Classification

Injuries to the thoracic and lumbar spine account for more than 50% of all spine fractures and a large portion of acute spinal cord injuries.¹⁷ Given this frequency and the significant impact of these injuries, significant advances have been made in the surgical treatment of thoracolumbar trauma. Nevertheless, although there has been progress in the invention and evolution of spinal instrumentation and surgical techniques, medical decision making in spine trauma remains controversial. To this day, fracture treatment can vary widely, from bracing to invasive 360-degree fusions, based on geographic, institutional, or individual preferences with little scientific basis.

A number of classification systems have been developed in an attempt to better define thoracolumbar trauma and aid treatment decision making. These systems are typically based on either anatomic structures (Denis three-column system) or on proposed mechanisms of injury (Ferguson and Allen).^79,80

In 1931 Watson-Jones pioneered one of the first spinal fracture grouping systems by type.⁸¹ This schematic categorization was based on diagnostic and treatment of flexion injuries.⁸² This was followed by Nicholl,⁸³ who developed the first detailed thoracic and thoracolumbar spine fracture classification scheme and attempted to define unstable versus stable fractures after trauma in a series of flexion and flexion-rotation injuries. This classification system was originally intended to guide the treatment and work status of injured miners. Nicholl emphasized the importance of the dorsal interspinous ligament in spinal stability.⁸³ Later, Holdsworth,⁸⁴ after clinical failures in immobilizing pure flexion fractures following the recommendations of Watson-Jones, further studied the importance of the spinal ligamentous complexes after thoracolumbar junction injuries. He classified fractures, according to their mechanism of injury, into four main types: flexion, flexion and rotation, extension, and compression. Holdsworth⁸⁴ further classified these fractures as unstable if the posterior ligamentous complex, consisting of the intervertebral disc, spinous ligaments, facet capsules, and ligamentum flavum, was disrupted. He noted that in compression, flexion, and extension injuries, the dorsal ligamentous complex is typically not ruptured and these fractures were therefore considered stable. However, he reported that flexion and rotational injuries were at a much greater risk for disruption of the dorsal ligamentous complex and subsequent instability. Subsequently, Rennie and Mitchell⁸⁵ added a fifth category of thoracolumbar junction fractures consisting of flexion-distraction fractures or seat belt injuries, based on the description and reporting of Chance.⁸⁶

Kelly and Whiteside⁸⁷ reported that without dislocation of the dorsal elements of the spinal column, neurologic injuries rarely occur. They classified fractures based on structural criteria and considered the spine to consist of not one, but two separate supportive columns (Fig. 66-9). The primary weight-bearing ventral column is composed of the vertebral bodies, and a second structural column consists of the posterior neural arches and ligaments. The structural classification scheme provided surgeons the ability to predict the degree of instability of the spine based on the degree of resulting structural damage after trauma. Based on this assessment, treatments were devised to enhance neurologic and spinal stability. Later, Louis⁸⁸ modified this structural classification scheme by proposing a third column. Louis’s three-column concept consisted of one ventral column, the vertebral bodies, and two dorsal columns involving each facet articulation (Fig. 66-10).

FIGURE 66-9 Axial CT of lumbar vertebral body illustrating Kelly and Whiteside’s two-column theory of spine stability, which classifies the spine into equal anterior and posterior columns of support.

FIGURE 66-10 Axial CT of lumbar vertebral body illustrating Louis’s three-column figure theory of spine structure. This classification system divides the spine into an anterior column consisting of the vertebral body and two equal posterior columns consisting of the facet complexes.

Technologic advances in the form of superior imaging studies have allowed a greater understanding of the pathoanatomy of spine trauma. Several biomechanical studies have documented that an isolated rupture of the posterior spinal ligamentous complex is insufficient to create instability.^89–91 Nonetheless, if the PLL, along with the posterior anulus fibrosus, is also disrupted, then the vertebral column will become unstable, particularly in flexion.

Denis⁷⁹ used the enhanced CT imaging techniques, along with in vitro biomechanical data, to modify spinal column theories further into a different three-column classification scheme (Fig. 66-11). In this classification, the ventral column consists of the ALL, the anterior anulus fibrosus, and the anterior half of the vertebral bodies. The middle column consists of the PLL, the dorsal anulus fibrosus, and the dorsal half of the vertebral bodies. Last, the posterior column, analogous to what Holdsworth defined as the dorsal ligamentous complex, consists of the bony neural arch, posterior spinous ligaments, and ligamentum flavum, as well as the facet joints. According to the Denis classification scheme, rupture of the dorsal ligamentous complex creates instability only if there is concurrent disruption of at least the PLL and dorsal anulus.

FIGURE 66-11 Axial CT of lumbar vertebral body illustrating Denis’s three-column classification scheme of spine stability. This classification system divides the spine into an anterior column consisting not only of the anterior half of the vertebral body but the anterior longitudinal ligament. The middle column consists of the posterior half of the vertebral body and the posterior longitudinal ligament. The posterior column consists of the facets, laminae, and ligamentous complex.

Denis⁷⁹ defined failure of the anterior column alone under compression (compression fracture) with an intact posterior column as a stable fracture (Fig. 66-12). Burst fractures were defined as being generated through an axial compressive load, and involved failure of the anterior and middle columns (Fig. 66-13). Severe tensile injuries resulted in seat belt fracture or flexion-distraction injuries, which involve a disruption of the posterior and middle columns with an intact anterior column that serves as a fulcrum or hinge (Fig. 66-14). The last category in Denis’s scheme is fracture-dislocations, which are defined as a mechanical failure of all three columns, making them extremely unstable injuries (Fig. 66-15).

FIGURE 66-12 L1 vertebral compression fracture (arrow). Note the posterior vertebral body’s height is maintained, and in the Denis classification only the anterior column is disrupted.

FIGURE 66-13 An 18-year-old man who sustained a 25-foot fall. Axial CT of L2 burst fracture details the canal encroachment of the retropulsed fracture (arrow). Note disruption of the posterior vertebral wall and splaying of the pedicles.

FIGURE 66-14 L2 Chance or seat belt fracture. Note this flexion-distraction injury splits the pedicle and facets (arrows), leaving the anterior column intact.

FIGURE 66-15 A 38-year-old man driven over by a truck presented with thoracic T7-8 dislocation and complete loss of motor function and sensation below the injury. The spine was fractured and dislocated, therefore separating all three columns of stability as detailed in the Denis classification.

Denis organized instability into three categories: mechanical, neurologic, or both mechanical and neurologic. Mechanical instability may result in a late kyphotic deformity. For instance, a seat belt or severe compression fracture with compromise to the dorsal ligamentous complex may result in the spinal column falling into kyphosis, rotating around the intact middle column because of the deficient dorsal tension band.

External immobilization and, when appropriate, operative reduction and stabilization, may prevent this progressive deformity. Neurologic instability may occur after a severe burst fracture in which the middle column has ruptured under axial loads. This disruption and retropulsion of bone fragments into the spinal canal predisposes patients to an increased risk for neurologic injury, especially with increased spinal motion. Denis⁷⁹ reported that in 20% of patients with severe burst fractures and dorsal ligamentous injuries that were treated nonoperatively with external immobilization, a subsequent neurologic deficit developed. Neurologic and mechanical instability may develop after a burst fracture or fracture-dislocation, with or without an initial neurologic deficit. These are very unstable injuries and according to Denis’s analysis require decompression and internal stabilization.

Magerl et al.⁹² developed a comprehensive classification scheme based on pathomorphologic criteria. This system is modeled on the AO (Arbeitsgemeinschaft für Osteosynthesefragen) long bone fracture classification (developed by Müeller, Schneider, and Willenegger) and consists of a grid with three major fracture types, subdivided into three more groups, which are further subgrouped into three more categories.⁹² The main categories are (A) compression injuries of the vertebral bodies, (B) distraction injuries that affect the anterior and posterior elements, and (C) axial torque or multidirectional injuries with translation that also affects the anterior and posterior elements. The severity of the fractures in this scheme increases as they progress from type A through type C. Although this classification system is extremely organized and comprehensive, it is underused clinically because of its complexity.

McCormack et al.⁹³ created a classification system based on a load-sharing principle that uses a graded point system reflecting the integrity of the vertebral bodies or anterior and middle columns. Points are based on the amount of vertebral body comminution, spread of fragments at the fracture site, and amount of corrected traumatic kyphosis (Fig. 66-16). Trauma associated with the highest degree of energy should result in the greatest dispersion and displacement of bone fragments. This classification can be applied before surgery to quantitatively estimate the extent of disruption of the anterior and middle columns. Patients with high point values (>6) have a large void or gap, resulting in the least supportive anterior and middle columns. Fractures with the greatest dispersion of fragments and least bone-to-bone contact result in the highest degree of cantilever bending loads on the pedicle screw implants, predisposing posterior instrumentation to failure.^15,94 This classification scheme assists the surgeon in deciding if ventral spine support is necessary after dorsal instrumentation, based on the premise that inadequate anterior column support will result in excessive loads being transferred to the dorsal elements (and instrumentation), thus increasing the risk for failure.

FIGURE 66-16 McCormack grading scheme or load-sharing classification. Comminution of fragments based on a sagittal CT reformat: A1, little (<30%), one point; A2, moderate (30–60%), two points; A3, gross (>60%), three points. Apposition of fragments based on an axial CT scan: B1, minimal, one point; B2, spread, defined as greater than 2 mm in less than 50% of the body, two points; B3, wide, defined as greater than 2 mm in greater than 50% of the body, three points. Kyphosis correction based on plain radiographs: C1, less than 3 degrees, one point; C2, 4 to 9 degrees, two points; C3, greater than 10 degrees, three points.

(Copyright Cleveland Clinic Foundation.)

In 2009, the Spine Trauma Group created the Thoracolumbar Injury Classification and Severity Score (TLICS) system to address many of its predecessors’ limitations.^95–97 The TLICS system defines injuries according to injury morphology, integrity of the posterior ligamentous complex, and neurologic status of the patient. It is the first thoracolumbar injury classification system to use injury morphology combined with the patient’s neurologic status and the critically important status of the posterior ligamentous structures in medical decision making.

Consequently, the TLICS system was designed to aid in medical decision making by providing both diagnostic and prognostic information with a weighted injury severity score. Stable injury patterns (TLICS <4) may be treated nonoperatively with brace immobilization and active patient mobilization. Unstable injury patterns (TLICS >4) may be treated operatively with the guiding principles of deformity correction, neurologic decompression if necessary, and spine stabilization followed by active patient mobilization.⁹⁵

So far, the TLICS system has shown good to excellent intraobserver and interobserver reliability in a number of countries, with both orthopedic surgeons and neurosurgeons, and throughout a spectrum of spine treatment providers with varying levels of experience.⁹⁵ The TLICS system has been tested in the setting of an academic trauma center, verifying that physicians in training (residents and fellows) can readily be taught the TLICS system and incorporate it into patient care.⁹⁵ Furthermore, use of the TLICS system has yielded greater than 90% agreement in decision making for the management of thoracolumbar trauma across a number of providers.⁹⁸

Although the TLICS system has demonstrated success, it has inherent limitations. To date, many of the investigations into the TLICS system have been performed by individuals involved with its development.⁹⁹ In addition, a prospective application of the TLICS system to the treatment of spine injuries is needed to define any improvements in care and patient outcomes compared with the use of conventional systems.

Treatment Options and Strategies

No definitive treatment algorithm has been universally accepted for thoracic spine injuries, despite the numerous classification systems that exist. Stability of the vertebral column over the thoracic and thoracolumbar region, like the remainder of the spine, depends on the integrity of the osseous and ligamentous components. Once these structures are disrupted, the stability of the vertebral column can become compromised, resulting in an unstable spine. One difficulty in treating these fractures is that spinal instability is difficult to assess, based on clinical and radiographic findings. White and Panjabi give the most detailed description of instability: “the loss of the ability of the spine under physiological loads to maintain relationships between vertebrae in such a way that there is either damage or subsequent irritation to the spinal cord or nerve roots, and in addition, there is development of incapacitating deformity or pain due to structural changes.”¹⁴ However, even this definition leaves a large degree of ambiguity because of the large spectrum of spinal disorders.

Nonoperative Strategies

Nonoperative treatment is indicated for stable injuries without the potential for progressive deformity or neurologic injury. One-column injuries such as compression fractures and posterior element fractures are stable by definition and can be treated nonoperatively unless excessive kyphosis is noted, which raises concern for increased pain and deformity in the future.

Treatment of two-column injuries, such as burst fractures, depends to a significant extent on the patient’s neurologic status. In neurologically intact patients, nonoperative treatment is generally recommended.¹⁴ A period of bed rest followed by mobilization in a thoracolumbosacral orthosis (TLSO) brace and continued close monitoring for increased kyphosis and neurologic changes are recommended.

Gertzbein demonstrated in a large study that kyphotic deformity greater than 30 degrees correlated with increased back pain.^6,56,82,100 This result has not been duplicated in other studies. There is an array of highly morbid complications that can arise from nonoperative treatment for a kyphosis of greater than 30 degrees. More specifically, acute to subacute neurologic deterioration from avoidance of surgery becomes the most serious untoward event. This has been proven by Denis et al.⁴⁵ who witnessed how, in 21% (6/29) of their patients in this series, a concerning and debilitating neurologic deficit developed after nonoperative treatment was undertaken. In a prospective study by Mumford et al. of 41 patients with a nonoperatively treated burst fracture, a neurologic deficit developed in 1 patient.¹⁰¹

Notwithstanding the aforementioned surgical experiences for kyphotic deformities, other authors such as Reid et al.¹⁰² and Cantor et al.⁴⁰ have not necessarily noted an abrupt, or even progressive, decline in neurologic status by recommending a nonsurgical approach for patients with thoracolumbar burst fractures. It appears that the incidence of neurologic worsening lies between 0% and 20%. The inherent stability of the preserved ligaments and osseous structures usually prevents acute instability; however, a low potential for chronic or glacial instability still remains. Glacial instability usually presents as mechanical pain but could also present as a neurologic deficit.

VCFs, as discussed earlier, consist of a loss of anterior column or ventral vertebral body height as a result of axial compression. Anatomically, these fractures are considered stable if the dorsal ligamentous complex, along with the dorsal vertebral body, is not disrupted. Neurologic function should not be impaired in these fractures because the dorsal cortex of the vertebral body is not violated and there is no encroachment of fracture fragments on or into the spinal canal.

In the elderly, symptomatic compression fractures associated with severe pain and functional morbidity, which have not responded to a minimum of 6 weeks of conservative management, have been treated with polymethylmethacrylate (PMMA) augmentation, either through vertebroplasty or through a cavitation and end-plate elevation procedure (Fig. 66-17). These techniques have been associated with significant improvements in patient function and pain relief.^93,103,104

FIGURE 66-17 Three levels of kyphoplasty (vertebral augmentation with polymethylmethacrylate).

Burst fractures, as defined by Denis,^45,79 are vertebral body fractures involving the anterior and middle columns, such that the ALL and vertebral body, including the dorsal vertebral body cortex, are disrupted (see Figs. 66-4, 66-6, 66-11, and 66-13). As stated earlier, a burst fracture in a neurologically intact patient without posterior ligamentous or dorsal element fractures is usually considered a stable injury. James et al.¹⁰⁵ confirmed this clinically in their reported series of patients with burst-type fractures with an intact dorsal bony architecture, all of whom became stable with a bracing regimen. Thoracic burst fractures (T1-10) make up a minor subset of burst injuries, representing approximately 5% to 10% of the total number of burst fractures. Thoracic burst fractures are inherently more stable because of the presence of the costovertebral ligamentous complex, along with the support of the rib cage.¹⁰⁶ Therefore, as with VCFs, conservative therapy using bracing and postural reduction has been the mainstay of treatment.^89,90,107

The incidence and degree of kyphosis and neurologic deterioration after a thoracic or thoracolumbar burst fracture are not known. In the neurologically intact patient with a mild kyphotic deformity (<15 degrees) and minimal dorsal ligamentous disruption, a bracing strategy may be appropriate¹⁰⁸ (Fig. 66-18). This is corroborated by Rajasekaran,¹⁰⁹ who in 2009 reviewed the major series of burst fracture management in the previous 20 years and found that the results of conservative treatment were equal to those of surgery and also carried fewer complications. He mentions, however, that surgery for burst fractures may have definite advantages in patients with polytrauma or in the rare event of neurologic deterioration. Thus, nonoperative treatment can be safely adopted in the management of thoracolumbar burst fractures with a normal neurologic status. However, significantly divergent splaying of the spinous processes on lateral plain radiographs, which implies dorsal ligamentous complex disruption, suggests the potential for progressive instability, and in such cases surgical intervention should be considered.

FIGURE 66-18 A 35-year-old man sustained a T4 burst fracture (arrow) with minimal retropulsion and normal strength on physical examination. He was treated in a thoracic brace with cervical extension and has had no neurologic decline or progression of kyphosis.

Brown et al.¹¹⁰ advocated nonoperative treatment of burst fractures with less than 50% of vertebral body collapse, less than 30 degrees of kyphotic deformity, and no more than 3 cm of offset from the standard sagittal vertical angle on lateral scoliosis films. These recommendations are supported by the findings of Cantor et al.,⁴⁰ where evidence of dorsal ligamentous complex disruption was present if there was greater than 30 degrees of kyphosis, greater than 50% loss of ventral vertebral body height, splaying of the spinous processes, facet fracture or subluxation, and pars interarticularis fracture. Brown et al.’s management protocol recommended immediate casting of the hemodynamically stable patient in a hyperextension body cast, followed by serial radiographs. Casts were maintained for 6 to 12 weeks, followed by a Jewett orthosis and then serial radiographs every 4 weeks. This management strategy facilitated early mobilization, reduced hospital stays and costs, and, when successful, avoided the risks of surgical therapy.

Nonoperative management therefore may be used in the neurologically intact patient, even with a large degree of spinal canal stenosis from retropulsed bone fragments, as long as there is no significant kyphosis representing significant disruption of the dorsal osteoligamentous complex.¹¹¹ CT has confirmed spontaneous remodeling through reabsorption of retropulsed bone fragments in the spinal canal in patients immobilized nonoperatively.⁴⁸ However, if there is a decline in the patient’s neurologic status during nonoperative treatment, operative intervention is indicated in the presence of documented instability or neural compression.¹⁰¹

Operative Strategies

Wood et al.¹¹² published the first prospective, randomized study comparing operative and nonoperative treatment of a thoracolumbar burst fracture in patients without a neurologic deficit. They found that operative treatment of patients with a stable thoracolumbar burst fracture and normal findings on the neurologic examination provided no major long-term advantage compared with nonoperative treatment.

In general, there are only a handful of strict surgical indications for thoracolumbar burst fractures. Severe burst fractures with a neurologic deficit and canal compromise should be treated surgically. Moreover, in patients who are neurologically intact but have evidence of disruption of the posterior longitudinal ligament, inferred from greater than 25 degrees of kyphosis on radiographs or direct visualization of rupture of the PLL on fat-suppressed sagittal T2-weighted MRI, surgery is warranted.

There has, however, been a trend toward performing short-segment instrumentation at the thoracolumbar junction in an effort to preserve motion at adjacent levels. In this case, the McCormack classification seems useful in determining which patients would require an anterior stabilization in addition to the posterior short-segment instrumentation.¹¹³

Because of loss of integrity of the posterior column, distraction injuries, seat belt injuries, and Chance fractures require surgical stabilization to restore the posterior tension band. Translation injuries, rotational injuries, and those that shatter through the disc space and ligamentous complexes from ventral to dorsal always require surgical stabilization.

If surgical management is chosen, the next step is determining the most appropriate approach: anterior, posterior, or both.^114,115 Many factors, including fracture morphology and neurologic status, can play a role in this decision. Patients with complete neurologic deficit who are no longer in spinal shock have very little chance of significant neurologic recovery. The primary goal of surgery in this group is realignment and stabilization, typically through a posterior approach.³⁸

Another option is anterior decompression and fusion with instrumentation. Surgeon preference often plays a role, as does fracture morphology. Concomitant lamina fractures with posterior canal compromise generally necessitate beginning with a posterior approach because of possible neural entrapment and dural tears.¹¹⁶

Flexion-distraction injuries result in disruption of the posterior and middle columns in tension.¹¹⁷ Very often, the anterior column remains intact, acting as a hinge. Surgical intervention for these fractures typically involves a posterior approach. Anterior approaches are not routinely used in these injuries, to preserve the intact anterior column.

Fracture-dislocation injuries result in disruption of all three columns and hence carry a high incidence of complete spinal cord injury. Therefore, the main objective of surgical intervention is solely to provide posterior stabilization, facilitating early mobilization and rehabilitation. Anterior decompression and stabilization is performed after posterior surgical realignment of the fracture in those rare instances in which a partial neurologic deficit exists in the presence of significant anterior neural compression.

Ventral versus Dorsal Approaches

When a partial neurologic deficit is present, improving residual canal compromise is also a goal of surgery. This situation most typically occurs with burst fractures. If performed early enough (generally within 72 hours), posterior instrumentation allows for distraction and correction of sagittal alignment and successful indirect decompression of the spinal canal. Laminectomy with transpedicular decompression also can improve the canal clearance achieved through a posterior approach. A ventral or dorsolateral approach may effectively decompress the neural elements in the setting of spinal cord compression. The ventral approach is particularly useful for decompressing midline ventral lesions and correcting severe kyphotic deformities.^11,48 Bohlman et al.^26,27 reported superior neurologic outcomes after a ventral, compared with a dorsal, procedure in the setting of an incomplete thoracic spinal cord injury. The major limitation of a ventral exposure is the potential surgical violation of the pleural and/or peritoneal cavities. McCormick²² reported the effective use of an extrapleural technique for the exposure of the ventral thoracic and thoracolumbar spine, thus avoiding violation of the pleural cavity.

Dorsal decompression by laminectomy after thoracic and thoracolumbar injuries has been shown to be ineffective and should not be performed as an isolated treatment strategy.^11,118 The surgical removal or destruction of the dorsal ligamentous complex, along with the dorsal osseous elements, may permit temporary neurologic recovery. However, the vertebral column may not be able to maintain its alignment with the loss of the dorsal tension band, and instability, along with the potential progression of a kyphotic deformity, may ensue (Fig. 66-19). The immediate result of removing the dorsal osseous components is dorsal migration of the spinal cord if the spine has a lordotic alignment. However, the normal, untraumatized spinal column at the thoracolumbar junction maintains a slightly kyphotic posture. Spine trauma typically results in an increase in the kyphotic deformity or angulation. Therefore, removing the dorsal tension band after trauma in the setting of ventral compression from bone fragments may result in further neurologic compromise, caused by tethering of the neural elements over ventral bony elements (bowstring effect).

FIGURE 66-19 Anterior corpectomy and decompression after a burst fracture, followed with an anterior iliac crest bone graft fusion with a Kaneda device.

Biomechanically, ventral as opposed to dorsal reconstruction and instrumentation strategies provide superior mechanical stability over an equal number of spinal segments to compressive loads.^57,119 A patient with midline ventral spinal cord compression, an incomplete neurologic injury, and an unstable thoracic or thoracolumbar junction burst fracture is most effectively treated with a ventral decompression and reconstruction procedure (Fig. 66-20). A variety of ventral instrumentation systems are available that may be applied to the ventral spinal elements after an adequate decompression and fusion procedure. Biomechanically, ventral bicortical screws provide a 25% to 50% increase in screw purchase strength compared with unilateral screws.¹²⁰

FIGURE 66-20 A 50-year-old man with an L2 burst fracture after a fall. A, Plain sagittal radiograph illustrating 8 degrees of kyphosis. B, He was treated in a body cast and then braced but had progressive back pain; follow-up radiographs illustrated progression of the kyphosis to 26 degrees.

An advantage of a dorsal approach is that it provides excellent visualization and access to the dorsal thecal sac. This is useful in certain fracture types because the reported incidence of thecal sac lacerations (with the potential for nerve root incarceration) after traumatic thoracic and thoracolumbar burst fractures is 7% to 16%.^121,122 The lumbar nerve roots are prone to entrapment through these lacerations, and a ventral approach will not provide access to repair this deficiency.¹²³ The presence of a central split or greenstick fracture of the spinous process on preoperative transaxial CT may be an indicator of a dural laceration, depending on its size and displacement during impact.¹²⁴

Surgical Stabilization Methods

Harrington rods were the first spinal implants widely used for the treatment of vertebral fractures.¹²⁵ The dorsal spinal elements are distracted to reduce and realign the vertebral column by ligamentotaxis.⁹ Unfortunately, this artificially applied distraction force can result in the loss of the normal spinal curvature (loss of lordosis or exaggeration of kyphosis), resulting in muscles and ligaments working at a biomechanical disadvantage.¹²⁶ Harrington rods perform relatively poorly in three-column injuries because of a predisposition to overdistraction and the relatively high incidence of rod breakage and hook cutout (7–10%).

Although Harrington instrumentation can be used, it has mostly been supplanted by newer segmental instrumentation systems initially developed for scoliosis. These systems use multiple fixed anchors along the fixation rod. Application of multiple forces at different points is possible, resulting in a relatively low incidence of fixation failure. Compression, distraction, and translation are all possible using the same construct. Initially, these systems used hooks (sublaminar, pedicle, and transverse process) for fixation, but most now allow for pedicle screw fixation as well.

Pedicle screw fixation allows for instrumentation of vertebrae with fractured or absent laminae. In addition, pedicle screw fixation allows for rigid bony purchase through all three columns. Because of this increased rigidity, it is often possible to use fewer segments for stable fixation, allowing the preservation of more motion segments. Preserving motion segments is of less importance in the thoracic spine because little motion is lost compared with the cervical and lumbar segments. However, limiting instrumentation of distal segments is important in thoracolumbar injuries.¹⁰⁶

The osseous structures are fused concomitantly with posterior instrumentation. Some surgeons fuse only the injured vertebral segments with subsequent staged removal of hardware. Others fuse the entire length of the instrumentation, which results in loss of motion at additional segments. As mentioned, this is of less importance in the thoracic spine. With modern segmental fixation, fewer segments need to be instrumented to provide stability, and generally, the entire instrumented region is fused.¹²⁷

Individual anatomic factors, such as the presence of lamina fractures, often dictate choice of anchors. In the thoracic spine, it is not uncommon for pedicles to be too small to allow screw placement. Depending on the injury, two to three segments of fixation above and below the level of injury usually are required if hooks alone are used. With pedicle screws, this often can be limited to one or two segments.

The condition of the anterior column also can affect instrumentation choices. If severe comminution or kyphosis is present, extending the length of the dorsal instrumentation should be considered. This will allow for added anterior column support toward the construct as a whole. This is often an issue with burst fractures, with which ventral strut graft fusion may be required.

Neurologic Decompression for Incomplete Injuries

Neurologic injuries are present in 42% of patients with thoracolumbar junction fractures.⁵⁶ Approximately 90% of patients with a thoracic fracture, excluding a VCF, have a concurrent neurologic injury, with 63% having a complete neurologic deficit.¹²⁸ Compression of the spinal cord after thoracic or thoracolumbar trauma is typically caused by a ventral retropulsed bone fragment from the vertebral body. Complete loss of neurologic function below the level of the injury usually occurs at the moment of trauma, and therefore removing the retropulsed bone in the setting of a complete neurologic injury (American Spinal Injury Association [ASIA] type A) rarely, if ever, enhances neurologic recovery.⁴⁸ However, in the presence of an incomplete neurologic deficit with persistent compression of the neural elements, a decompressive procedure may maximize the potential for neurologic recovery.⁸

Hence, timing of surgery becomes an important issue in the treatment of thoracic spine fractures. Progressive neurologic deficit in the presence of continued canal compromise is an accepted indication for immediate decompression and stabilization. Quite often, patients with thoracic spine fractures have concomitant injuries, making the timing of spinal stabilization difficult to plan. Some studies suggest that patients with thoracic spine fractures treated within 72 hours, regardless of concomitant injuries, do much better physiologically after surgery than those in whom stabilization is delayed. Early fixation results in less time in the intensive care unit, less ventilator support, a decreased rate of pulmonary complications, and less overall time in the hospital. Boerger et al.⁴⁸ performed a meta-analysis of the world literature to analyze surgical outcome after decompression of the spinal cord after thoracolumbar burst fractures. Patients with an incomplete neurologic deficit who underwent an operative decompression and stabilization procedure in less than 72 hours were shown to have an enhanced neurologic recovery compared with nonoperatively treated patients.^48,129 Operative therapy has also been shown to decrease pain, reduce periods of postural reduction or bed rest, and improve sagittal alignment.⁵⁶ At present, surgical decompression in patients with a complete neurologic injury has not demonstrated true benefit in terms of overall neurologic improvement.²⁷

Additional Operative Considerations

Fracture-dislocations are the most unstable of traumatic vertebral column injuries. The fractures are created by significant high-energy loads that result in a complete dissociation of the osseous structures and ligamentous complexes. Typically these carry a complete loss of neurologic function^45,130 (see Fig. 66-15). Flexion-distraction-dislocation injuries have a significant distraction component and differ from seat belt–type injuries in that there is a large rotatory or torque component that causes a disruption of all three spinal columns.⁷⁹ An injury of this type in the thoracic region almost always results in a complete spinal cord injury. Such injuries are associated with the highest incidence of concurrent neurologic injuries.⁷⁹ Denis reported that over 50% of patients with this fracture subtype had a complete paraplegia.⁷⁹

Patients with a complete neurologic injury involving the thoracic spine may frequently benefit from surgical intervention to realign a deformity, provide immediate stability, and prevent further or future neurologic injury. This expedites their transfer to a facility so they can begin rehabilitation and can subsequently be placed erect without further injury to the spinal cord proper.¹³¹ Postural reduction and bed rest mandate at least 6 to 12 weeks of prolonged immobilization before the spine heals enough to attain any degree of intrinsic stability.¹³⁰

Indirect augmentation of the anterior column through a dorsal transpedicular approach, without removal or replacement of the contiguous intervertebral discs, does not appear to provide sufficient anterior column support. Alanay et al.¹³² demonstrated that short-segment transpedicular screw fixation through a dorsal approach failed equally (approximately 50%) with and without transpedicular bone graft augmentation. The lateral extracavitary approach provides access to both the ventral and dorsal portion of the vertebral column through a single dorsal incision. However, this approach has limited usefulness in thoracic and lumbar trauma because of its high incidence of associated morbidities. For example, Resnick and Benzel¹³³ reviewed their series of 33 trauma patients treated with this approach and reported a 55% incidence of morbidity.

Summary

The care of patients with thoracolumbar spine trauma with or without neurologic deficits has evolved dramatically over the past 30 years. The development of more effective spinal instrumentation and anesthesia techniques coupled with the establishment of spine injury care centers where immediate treatment and rehabilitation can be administered successively has definitely improved the care of these patients. Despite these advances, the majority of patients with thoracolumbar injuries are still treated nonoperatively with cast or brace immobilization and early ambulation. More aggressive treatment is guided by the use of classification systems that detail the mechanism of injury, the degree of compromise of spinal structures, and the potential for late mechanical instability or neural injury. Even now, the goal of treatment remains attainment of spinal stability with protection or improvement of the patient’s neurologic status, allowing rapid and maximal functional recovery. Guidelines such as the TLICS system are now in place to help the clinician make better-educated decisions as to which patients to treat operatively and which to manage nonoperatively.

Successful management of thoracolumbar spine injuries protects the patient from further spinal deformity and neurologic deficit. As we have seen here, there is no clear consensus as to the absolute indications for surgical intervention in patients with many types of thoracolumbar fractures.