Fractures of the thoracolumbar spine can be classified into 4 groups based on the mechanism of injury: flexion-compression, axial-compression, flexion-distraction, rotational fracture-dislocation. The mechanism of injury is used interchangeably with the name of the fracture. These major fractures are presented below in escalating order of severity.
Flexion-compression mechanism (wedge or compression fracture)
The flexion-compressionmechanism usually results in an anterior wedge compression fracture. As the name implies, the anterior column is compressed, with varying degrees of middle and posterior column insult. (See the image below.)
Anteroposterior and lateral radiographs of an L1 osteoporotic wedge compression fracture.
View Media Gallery
Ferguson and Allen developed a classification systemthat characterizes 3 distinct patterns of injury, as follows [6] :
-
The first pattern involves anterior column failure while the middle and posterior columns remain intact. Imaging studies demonstrate wedging of the anterior component of the vertebral bodies. Loss of anterior vertebral body height is usually less than 50%. This is a stable fracture.
-
The second pattern involves both anterior column failure and posterior column ligamentous failure. Imaging studies demonstrate anterior wedging and may indicate increased interspinous distance. Anterior wedging can produce a loss of vertebral body height greater than 50%. This has an increased possibility of being an unstable injury.
-
The third pattern involves failure of all 3 columns. Imaging studies demonstrate not only anterior wedging, but also varying degrees of posterior vertebral body disruption. This is an unstable fracture. Additionally, the possibility exists for cord, nerve root, or vascular injury from free-floating fracture fragments dislodged in the spinal canal.
Axial-compression mechanism
The axial-compression mechanism results in an injury called a burst fracture, and the pattern involves failure of both the anterior and middle columns. Both columns are compressed, and the result is loss of height of the vertebral body. Five subtypes are described, and each is dependent on concomitant (namely rotation) extension and flexion: (1) fracture of both endplates, (2) fracture of the superior endplate (most common), (3) fracture of the inferior endplate, (4) burst rotation fracture, and (5) burst lateral flexion fracture. [7]
McAfee classified burst fractures based on the constitution of the posterior column (stable or unstable). [8] In stable burst fractures, the posterior column is intact; in unstable burst fractures, the posterior column has sustained significant insult. Imaging studies of both stable and unstable burst fractures demonstrate loss of vertebral body height. Additionally, unstable fractures may have posterior element displacement and/or vertebral body or facet dislocation or subluxation. As with a severe wedge fracture, the possibility exists for a cord, nerve root, or vascular injury from posterior displacement of fracture fragments into the canal. Denis showed that the frequency rate of neurologic sequelae could be as high as 50%. [9] Recommendations call for detailed imaging studies to identify the possibility of canal impingement, which requires decompressive surgery.
Flexion-distraction mechanism
The flexion-distraction mechanism results in an injury called a Chance (or seatbelt) fracture. This pattern involves failure of the posterior column with injury to ligamentous components, bony components, or both. The pathophysiology of this injury pattern is dependent on the axis of flexion. Several subtypes exist, and each is dependent on the axis of flexion and on the number and degree of column failure.
The classic Chance fracture has its axis of flexion anterior to the anterior longitudinal ligament; this results in a horizontal fracture through the posterior and middle column bony elements along with disruption of the supraspinous ligament. This is considered a stable fracture. Imaging studies show an increase in the interspinous distance and possible horizontal fracture lines through the pedicles, transverse processes, and pars interarticularis.
The flexion-distraction subtype has its axis of flexion posterior to the anterior longitudinal ligament. In addition to the previously mentioned radiographic findings, this type of injury also has an anterior wedge fracture. Because all 3 columns are involved, this is considered an unstable injury.
If the pars interarticularis is disrupted in either type of fracture, then the instability of the injury is increased, which may be radiographically demonstrated by significant subluxation. Neurologic sequelae, if they occur, appear to be related to the degree of subluxation.
Rotational fracture-dislocation mechanism
The precise mechanism of rotational fracture-dislocation is a combination of lateral flexion and rotation with or without a component of posterior-anteriorly directed force. The resultant injury pattern is failure of both the posterior and middle columns with varying degrees of anterior column insult. The rotational force is responsible for disruption of the posterior ligaments and articular facet. With sufficient rotational force, the upper vertebral body rotates and carries the superior portion of the lower vertebral body along with it. This causes the radiographic "slice" appearance sometimes seen with these types of injuries.
Denis subtyped fracture-dislocations into flexion-rotation, flexion-distraction, and shear injuries. [9] The flexion-rotation injury pattern results in failure of both the middle and posterior columns along with compression of the anterior column. Imaging studies may demonstrate vertebral body subluxation or dislocation, increased interspinous distance, and an anterior wedge fracture.
The flexion-distraction injury pattern represents failure of both the posterior and middle columns. The pars interarticularis is also disrupted. Imaging studies demonstrate an increased interspinous distance and fracture line(s) through the pedicles and transverse processes, with extension into the pars interarticularis and subsequent subluxation.
The shear (sagittal slice) injury pattern results in a 3-column failure. The combined rotational and posterior-to-anterior force vectors result in vertebral body rotation and annexation of the superior portion of the adjacent and more caudal vertebral body. Imaging studies demonstrate both the nature of the fracture and dislocation.
Each of these fractures is considered unstable. Neurologic sequelae are common.
Minor Fractures
Minor fractures include fractures of the transverse processes of the vertebrae, spinous processes, and pars interarticularis. Minor fractures do not usually result in associated neurologic compromise and are considered mechanically stable. However, because of the large forces required to cause these fractures, associated abdominal injuries may occur. In this context, the index of suspicion for associated injuries should increase and the physician should examine the patient for associated injuries.
Fractures Secondary to Osteoporosis
Osteoporosis causes fractures of the vertebrae and fractures of other bones such as the proximal humerus, distal forearm, proximal femur (hip), and pelvis (see Osteoporosis). Women are at greatest risk. The prevalence rate for these fractures increases steadily with age, ranging from 20% for 50-year-old women to 65% for older women. Most vertebral fractures are not associated with severe trauma. Many patients remain undiagnosed and present with symptoms such as back pain and increased kyphosis. The presence of a significant vertebral fracture is associated with increased mortality. Patients with these fractures have a relative risk of death that is 9 times greater than healthy counterparts. Approximately 20% of women with vertebral fractures have another fracture of a different bone within a year. [10]
Efforts are currently underway to reliably predict who is at risk for these fractures. Bone densitometry is used to assess relative bone strength and fracture risk. Risk factors for osteoporosis fractures include postmenopausal age, white race, and low bone density prior to menopause. Predicting which patients are at risk using risk factor analysis or bone imaging allows for the administration of specific treatments that promote bone deposition or delay resorption. Prevention of fractures is critical and should include exogenous calcium and an appropriate exercise regimen. Many hormonal therapies are also available, including raloxifene and calcitonin.
The American College of Physicians developed a guideline for the pharmacologic treatment of low bone density or osteoporosis to prevent fractures. [11]
Pathologic Fractures
Pathologic fractures are the result of metastatic disease of primary cancers affecting the lung, prostate, and breast. Kaposi sarcoma can also result in vertebral body fractures. Occasionally, cancer affects the spine itself or is the result of meningeal neoplasia. Pathologic fractures tend to affect the vertebral body at both the thoracic and lumbar levels. They cause kyphotic deformity and may result in compression of the cord or cauda equina. If the patient has neurologic deficits, consider emergent radiotherapy, steroid use, and surgical decompression and stabilization. (See the image below.)
Fluoroscopic view of a kyphoplasty procedure.
View Media Gallery
Fractures Secondary to Infection
Pott disease (tuberculosis spondylitis) results from the hematogenous spread of microbacteria to the spine [see Pott Disease (Tuberculous Spondylitis)]. Other bacteria can be spread to the spine and cause osteomyelitis. As bacteria proliferate, vertebral damage occurs and primarily affects the vertebral bodies. As in the case of pathologic fractures, associated fractures and an increase in kyphotic deformity may be present. Treatment includes antibiotics. The presence of a neurologic deficit may prompt instrumentation and stabilization of the spine.
Patients With Special Considerations
Elderly patients usually have significant osteoporotic disease and degenerative bone disease. These patients may experience a significant fracture even from a relatively minor, low-energy mechanism of injury. Compression fractures in both the thoracic and lumbar regions are common. These patients also may have pathologic fractures. Central cord syndrome is common for patients who develop neurologic deficits. For elderly patients with stable fractures, early mobilization is important to decrease morbidity and mortality.
Special consideration should be given to pediatric patients with significant trauma to the thoracic or lumbar spine. Because the skeleton is immature and the ligaments are elastic, significant force must be generated to cause a fracture, especially those associated with neurologic deficits. One entity that occurs in pediatric patients is spinal cord injury without radiographic abnormality. If injury and neurologic deficits are strongly considered, perform imaging studies such as computed tomography (CT) or magnetic resonance imaging (MRI) scans. If the mechanism or circ*mstances are not consistent with the injury, consider abuse or neglect. Pediatric patients should be examined for additional injuries and bruises.
Patients in altered mental states pose a diagnostic challenge. In the absence of a reliable history and review of systems, findings from the physical examination and radiographic studies can help the physician assess vertebral injuries. In altered or intubated patients with other significant fractures such as pelvic fractures, multiple rib fractures, or scapular fractures, the physician should have a heightened index of suspicion for vertebral fractures. Once these patients have been stabilized, abdominal and chest radiographs may be supplemented with lateral views to reduce the likelihood of a missed vertebral fracture.
