Introduction
Background
Fracture of the lumbar spine can occur whenever forces applied to the lower spinal column exceed the strength and stability of the spinal column unit. Common injuries resulting in fractures of the lumbar spine include fall from a height; motor vehicle and motor vehicle and pedestrian accidents; and penetrating trauma, including gunshot wounds and stabbings. Unstable injuries to the pelvis often are associated with injury to the sacral plexus and the lower lumbar spine.
The goal of the diagnostic radiologist is to identify lumbar spine fractures correctly, to identify and correlate neurologic injury to vertebral fractures, to advise the surgeon (who best defines the extent of injury to supporting structures), to gauge the risk to the spinal cord, and to judge the stability of postoperative fixation. This article highlights the typical patterns of injury and focuses on the imaging methods that are most useful in the clinical practice of trauma radiology.
For excellent patient education resources, visit eMedicine's Back, Ribs, Neck, and Head Center. Also, see eMedicine's patient education article Vertebral Compression Fracture.
Pathophysiology
Fractures of the lumbar spine occur any time the combined forces of compression, distraction, and rotation exceed the strength of the spinal column. The predominant force determines the nature of the fracture dislocation.
An example of a predominately distractive injury is a Chance fracture of the spine. A Chance fracture usually is a lower thoracic spinal or upper lumbar fracture with posterior ligament rupture. It represents a variant of the flexion distraction injury pattern. Usually, a minor anterior vertebral compression occurs (see Images 13-14).
In a Chance fracture, the anterior column fails in tension, whereas a flexion distraction fracture primarily involves compression of the anterior column and distraction of the middle and posterior columns. The distinction is principally the relative degree of posterior ligamentous injury versus anterior compression. Of patients with flexion distraction injuries, 50% have rupture of the interspinous ligament, ligamentum flavum, facet capsule, posterior annulus, and thoracodorsal fascia. A traumatic compression fracture in a young patient (after a motor vehicle accident) should be considered a possible Chance fracture. Most Chance fractures that involve the lumbar spine occur at the L1 vertebral level (see Image 15); however, a similar injury pattern may occur at the L2 (see Image 16).
Fractures associated with flexion are more common in the upper lumbar levels and less common in the lower lumbar and sacral areas. The lower lumbar spine (L4-S1) is stabilized by the large paraspinal muscles and the limited range of motion of the L5-S1 interspace. However, at the L1-L3 levels, a fulcrum of increased motion results in the potential for a combination of acute hyperflexion and rotation (see Images 17-18).
Because the spinal cord terminates at the T12-L1 level, lower thoracic and upper lumbar spinal injuries at this level most commonly cause bladder and bowel signs and decreased movement and sensation in the lower extremities.
A vertical compression force (see Image 19) may result in compression of the endplates of the vertebral bodies, or it may result in significant deformity and spinal canal compromise (see Images 20-26). The injury pattern may be primarily posterior, resulting in spinal cord injury (see Image 27). Significant anterior vertebral body injury can occur without causing spinal cord injury (see Images 28-29).
Distractive injuries more commonly occur in the upper lumbar spine resulting from fixation of the pelvis with violent pulling of the upper spine. Fixed neurologic injury is common if the distraction is significant (see Image 30).
Axial rotation occurs in the upper lumbar region. If the rotational forces are sufficiently great, a combined fracture and rotational subluxation occurs (see Image 31). Injury to the conus medullaris results.
Pathologic fractures due to metastatic or metabolic bone disease can occur with relatively minor trauma (see Images 31-32). Compression of the lateral nerve roots or the conus medullaris results in variable degrees of weakness and pain.
Frequency
United States
In young adults, lumbar spine fractures are commonly associated with multisystemic blunt trauma. The rate of spinal fractures in a serious motor vehicle accident is 5-6%; the L1, L2, and T12 levels are most frequently injured. Injuries are most common in patients aged 30-39 years and least common in persons younger than 18 years. Compression fractures are the most typical injury in the lumbar spine. The area of the lumbar spine most often injured is the thoracolumbar junction.
International
Spinal fractures in the lumbar spine occur in people in all nations as a result of accidents and industrial injuries. The incidence of such injuries is proportionate to the number of motorized vehicles. In the developing nations of Asia, spinal fractures frequently are associated with spinal tuberculosis as well. Trauma related to military action occurs on a regional basis, based on current international relations.
Mortality/Morbidity
In most lumbar fractures, the primary morbidity in patients is pain. Spinal pain may be seen in patients with acute fractures and fractures associated with advanced age.
Mortality associated with lumbar spine fractures is primarily the result of associated injuries to the spleen, liver, aorta, and pelvis. Delayed mortality may be associated with urinary infections if the injury resulted in a neurotropic dysfunction of bladder control. Morbidity related to lumbar spine trauma often includes lower extremity weakness or paralysis and chronic pain.
Neurologic recovery is best for fractures with kyphosis of greater than 15° and minimal compromise of the spinal canal. Such injuries have been associated with a greater than 90% likelihood of neurologic recovery. Fractures with kyphosis of less than 15° and maximum canal compromise are associated with a less than 50% likelihood of neurologic recovery. Fractures with kyphosis of 15° or less and maximum canal compromise at the level of the ligamentum flavum are associated with variable neurologic recovery. The prognosis for neurologic recovery can be estimated on the basis of the initial radiographic findings. A kyphosis of greater than 15° with only minimal deformity of the posterior aspect of the lumbar vertebral body is associated with a good prognosis.
Race
- Bone density may be greater in some black men and women than in others.
- Compression fractures of elderly women are more common in white women than in black women.
- Postmenopausal estrogen use is associated with an increased likelihood of back pain and impaired back function in elderly white women (see Intervention).
Sex
- Because young males participate in at-risk behaviors and have more accidents, they are more likely than others to have fractures of the lumbar spine.
- The occupational risk of a fall from a great height is more common among men than women.
- Compression fractures are more common among older women than other individuals.
Age
Two age distributions are noted in the occurrence of lumbar spine fractures.
- An increased frequency of abnormal radiologic findings of the lumbar spine is noted in young athletes who participate in various sports. Young elite skiers (ski jumpers) have a significantly higher rate of anterior endplate lesions of the lumbar spine than that of control subjects. This difference has been attributed to excessive loading and repetitive high-velocity trauma to the immature spine. Other high-risk activities such as rock climbing, motorcycle racing, and skydiving are associated with an increased occurrence of compression and burst fractures of the lumbar spine.
- At the other end of the age spectrum, compression fractures more commonly occur in middle-aged and older women and men than in others; often, minimal trauma occurs.
Anatomy
The lumbar vertebral bodies have a vertical height that is less than their horizontal diameter. An intervertebral disk lies between each lumbar vertebral body. The disk consists of the outer annulus fibrosis and nucleus pulposus (see Image 1). Generally, 5 similar lumbar vertebral bodies are distinguished from the thoracic bodies by the absence of rib facets (see Image 2). The pedicles project from the upper portion of the vertebral body. The spinous process is primarily horizontal in orientation, while the posterior inferior border projects below the upper level of the spinous process below.
The laminae of the lumbar region are thick and project below the pedicles. The transverse processes are long and thin with a slant that is both upward and backward. The articular facets are heavier than those of the thoracic or cervical spine. The superior facets face medially, while the inferior facets face laterally. The interarticular joints are in a parasagittal plane (see Image 3). When viewed in an oblique projection, the outline of the facets and the pars interarticularis appear like the neck of a Scottie dog (see Image 4).
The movement of the lumbar spine is largely confined to flexion and extension with a minor degree of rotation. The region between the superior articular process and the lamina is the pars interarticularis. A spondylolysis occurs if ossification of the pars interarticularis fails to occur.
The primary ligamentous support for the lumbar spine is the anterior longitudinal ligament, the posterior longitudinal ligament, the attachments of the annulus fibrosis, the facet joints, and the interosseous ligaments between the spinous processes (see Images 5-6).
Presentation
Traumatic compression fractures represent a primarily vertical load injury with anterior or lateral flexion causing failure of the anterior column. The middle column remains intact and may act as a hinge (see Image 6). These fractures are usually stable and rarely involve neurologic compromise.
The Denis classification system includes 4 types of compression fractures:
- Type A - Involvement of both endplates
- Type B - Involvement of the superior endplate
- Type C - Involvement of the inferior endplate
- Type D - Buckling of the anterior cortex with both endplates intact
A lumbar spine burst fracture results from hyperflexion, which produces wedge compression of one or more vertebral bodies. Because of the rigidity of the ribcage, most of these fractures occur at the L1 or L2 level. The lumbar spinal canal is relatively wide in relation to the lower spinal cord and the conus; thus, lower thoracic spinal cord injuries are commonly incomplete. Kyphosis greater than 30° requires internal stabilization to prevent further deformity (see Image 18). Dural laceration with impaled nerve roots can be anticipated at the time of surgery if a patient with neurologic damage has a burst fracture of a vertebral body combined with a laminar fracture at the same level.
The principal treatment for unstable lumbar spine fractures is surgical fixation with spinal canal decompression as needed (see Images 34-37). The area of injury commonly includes the lower thoracic and upper lumbar spine (see Image 38). Instability is usually associated with kyphosis of 20° or more. The primary posterior approach is accomplished by means of the Harrington rod system. Adverse effects resulting from the locking of vertebral segments and incomplete reconstitution of the vertebral height have been reported.
An alternative posterior approach involves pedicular fixation in which 2 segments are fused. The procedure results in both fracture reduction and fixation. The injured vertebra also is grafted through the pedicle. Clearance of bone fragments from within the spinal canal is an important goal for most surgical approaches to lumbar spine fractures. Patients with complete paraplegia can be expected to remain unchanged.
Preferred Examination
A general outline for the evaluation of acute multiple trauma involving the spine is shown in Image 7.
At the least, standard anteroposterior (AP) and lateral radiographs should be obtained in all patients. Oblique views are useful if the AP and lateral views demonstrate scoliosis or a questionable defect of the posterior spinal elements. Flexion and extension views are helpful if subluxation is detected or if a chronic injury may be present. In all patients with compression fracture, the anterior height of the vertebral body is diminished, whereas the posterior height remains within normal limits. No subluxation of vertebral bodies is present. The anterior compression is less than 40% unless a burst fracture is present (see Images 8-9).
After conventional radiography, CT is the primary means used to depict the posterior elements, which is necessary to exclude posterior instability and vertebral body deformity. CT scans are better in depicting the spinal canal and in estimating the degree of neural compromise. In a burst fracture, CT best demonstrates posterior spinal element involvement (see Image 10). Axial CT scans fail to demonstrate subtle horizontally oriented injuries of the vertebral bodies, pedicles, or laminae. Also, axial CT scans may not depict minimal vertebral body compression fractures. The use of frontal and sagittal reformation, together with thin primary imaging sections, can overcome most of these limitations (see Images 11-12).
Many patients who present with lumbar spine injury have pulmonary, rib, or vascular injury. The expense and delay of obtaining routine CT scans of the lumbar spine are not justified. A review of the bone windows of thoracic and abdominal CT scans reveals most major deformities that are associated with Chance fracture, distraction injury, and burst vertebral fractures. More complex injuries can be studied later if necessary, but multisection CT studies can be reformatted to examine the lumbar spine in a lateral (sagittal) view. The use of MRI in spinal trauma should be linked to neurologic examination or unexplained severe spinal pain.
MRIs of the lumbar spine provide information that is not available with CT scans. Early in an injury, T1-weighted spin-echo (SE) axial and sagittal images may demonstrate the high signal intensity related to acute hemorrhage, including the rare complicating epidural hemorrhage. Both T2-weighted fast spin-echo (FSE) and fluid-attenuated inversion recovery (FLAIR) images demonstrate the high signal intensity associated with edema of bone marrow fat. Gradient-echo T2-weighted images best outline the shape and structure of the vertebral body and the posterior spinal elements. These MRIs are superior to CT scans for the detection of a posttraumatic herniated disk, ligamentous edema, and spinal cord compression. Gadolinium diethylenetriamine pentaacetic acid (Gd-DTPA) contrast enhancement should be used in patients with suspected metastatic disease and septic spondylosis, diskitis, or osteomyelitis (see Image 16).
Gadolinium-based contrast agents (gadopentetate dimeglumine [Magnevist], gadobenate dimeglumine [MultiHance], gadodiamide [Omniscan], gadoversetamide [OptiMARK], gadoteridol [ProHance]) have recently been linked to the development of nephrogenic systemic fibrosis (NSF) or nephrogenic fibrosing dermopathy (NFD). For more information, see the eMedicine topic Nephrogenic Fibrosing Dermopathy. The disease has occurred in patients with moderate to end-stage renal disease after being given a gadolinium-based contrast agent to enhance MRI or MRA scans. As of late December 2006, the FDA had received reports of 90 such cases. Worldwide, over 200 cases have been reported, according to the FDA. NSF/NFD is a debilitating and sometimes fatal disease. Characteristics include red or dark patches on the skin; burning, itching, swelling, hardening, and tightening of the skin; yellow spots on the whites of the eyes; joint stiffness with trouble movingor straightening the arms, hands, legs, or feet; pain deep in the hip bones or ribs; and muscle weakness. For more information, see the FDA Public Health Advisory or Medscape.
Occult injury associated with lumbar vertebral body compression may be better assessed by using nuclear medicine bone scanning than with other techniques. Technetium-99m hydroxydimethylpyrimidine (HDP) is most commonly administered for this test. Chronic injuries demonstrate moderately increased activity, whereas acute fractures usually demonstrate a focally increased activity.
Limitations of Techniques
Radiographs may not clearly demonstrate the posterior spine elements, and excluding a Chance fracture can be difficult. Also, although most compression fractures in older patients are benign, a significant number of spontaneous compression fractures are related to metastatic disease. Follow-up imaging with contrast-enhanced MRI is indicated in all patients in whom a mass is noted and in all patients in whom a primary malignancy is suspected. Axial CT scans may fail to depict subtle horizontally oriented injuries of the vertebral bodies, pedicles, or laminae. Axial CT scans also may miss minimal vertebral body compression fractures. The use of frontal and sagittal reformation, together with thin primary image sections, can overcome most of these limitations. The resolution of MRIs used in the detection of spinal fractures is limited. Although gradient-echo and T1-weighted SE images outline fractures better, minimally displaced fractures are difficult to see.
Although nuclear medicine bone scans are sensitive to the processes that destroy or injure bone, a positive area of increased uptake on a bone scan is not specific for fracture. The fracture may not be detected for as long as 72 hours after an injury. The resolution of fracture outlines is poor with nuclear medicine studies. Large osteophytes and intervertebral disk narrowing with vertebral endplate sclerosis may appear as areas of increased activity on standard nuclear bone scans. CT scans of the lumbar region may help making the diagnosis if the results of a bone scan are positive. MRI is most effective in the identification of neoplasm and osteomyelitis.
Differential Diagnoses
| Arachnoid Cyst | Osteoporosis, Involutional |
| Hemangioma, Bone | Septic Arthritis |
| Multiple Myeloma | Spondylolisthesis |
| Osteomalacia and Renal Osteodystrophy | Spondylolysis |
| Osteomyelitis, Chronic |
More on Lumbar Spine, Trauma |
 Overview: Lumbar Spine, Trauma |
| Imaging: Lumbar Spine, Trauma |
| Follow-up: Lumbar Spine, Trauma |
| Multimedia: Lumbar Spine, Trauma |
| References |
| Next Page » |
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Further Reading
Keywords
Chance fracture, pathologic fracture, burst fracture, insufficiency fracture, spondylolysis deformity, spondylolisthesis, lumbar spine trauma, lumbar spine injury, lumbar spine fracture
