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The fracture that will be discussed in this assignment is chance and burst fractures of thoracolumbar spine. The author will briefly describe these fractures and outline their mechanism of injury and identify their clinical complication in section one. In section two, plain radiography, CT and MRI will be discussed as an appropriate imaging procedure in the diagnosis of a chance fracture of the thoracolumbar spine.
Burst fracture are divided into five subtypes Burst: fracture of both endplates, fracture of superior endplate, fracture of the inferior endplate, burst rotation fracture and burst lateral flexion fracture . Burst fracture can be both stable and unstable depending on the severity of the injury pattern. A stable fracture does not involve any neurological injury. This is normally seen in plain x ray where the angulations of the spine is less than 20 degree and the amount of spinal canal compromise is less than 50% (refer). Unstable burst fracture is when there is a present of neurological injury. This type of fracture is normally demonstrated on plain x ray when the angulations of the spine is greater than 20 degree (ref).
Burst fracture is a traumatic spinal injury which involves compressive failure of anterior and middle column. The mechanism injury for burst fractures usually happens from high energy axial load after a motor vehicle accident or falling from significant height. Burst fractures can occur in cervical and thoracolumbar spine. However, Burst fractures are most seen in thoracolumbar spine between T9-L5 levels causing failure of the middle and anterior column(ref). This includes the anterior half of the vertebral body/disc and the posterior body. The majority of burst fractures are associated with degree of canal compromise and bony fragment resulting in serious spinal cord injury. Neurologic injury has been reported to occur in 30% of the patients with thoracolumbar burst fractures (RE). Another complication can be loss of control the bowel and bladder. Burst fracture can cause severe pain at the site of the fracture.
Describe by Chance (1948), Chance fracture is a flexion injury most often occurs at the thoracolumbar junction between T10-L2 in adult or midlumbar spine in children (ref). This type of fracture is most commonly occurs in a motor vehicle accident passengers wearing a lap seat belt. The mechanism of injury is an acute forward flexion of the spine during a sudden deceleration, which causes the spine above the belt to be pushed forward and distracted from the lower fixed part of the spine.This fracture involve a horizontal splitting of the vertebra that begins with the spinous process or lamina and extend interiorly through pedicles and the vertebra body. The vertebra body tends to have a wedge compression and the posterior elements of the vertebra are distracted. Chance fractures can be associated with intra-abdominal injuries in approximately 50% of cases, which is thought to result from the compression of organs between the lap belt anteriorly and the bony vertebral column posteriorly (ref). These involve particularly tears and transections of the pancreas, duodenum, jejunum and menstery are common (ref). Injuries to spinal cord are rare but the spinal nerves may be injured resulting in bowel and bladder signs.
Chance fracture can be both stable and unstable. Unstable chance fracture is when there is osseous disruption cross the posterior arches, pedicles and vertebra, a horizontal fracture involves both pedicles with extension anteriorly through inferior third of the vertebral body. Chance's fractures with anterior vertebral extension through superior third of vertebra are unstable. Fractures with anterior horizontal vertebral disruption in the posterior half of the body are stable.
Plain film is the primary diagnostic imaging to be considered in patients with suspected chance fracture of thoraco-lumbar spine. Patients will undergo two view; anterior-posterior and cross table lateral radiograph of thoracic and lumbar spine. AP view demonstrates the loss of vertebral body height, a horizontal fracture through pedicles, widening of interspinous spaces and facet joint separation. AP view may also indicates an increase of facet joints, a transverse fractures across the transverse processes and laminae.
Lateral views are useful in demonstrating superior endplate fracture, anterior wedging deformity, anterior wall cortex irregularity, and misalignment of the vertebral bodies, fracture through the laminae and pedicles. In addition, distraction of the posterior elements is best seen on the lateral view than AP view.
Plain film radiographic is readily available in all hospitals. It is reliable, quick method for evaluation of Chance fractures and it is relatively inexpensive compare to computed tomography. The exact position and size of fracture fragments may be difficult to identify correctly, and therefore is inadequate for preoperative planning of unstable chance fracture. According to (ref), all patients with chance fracture evident on the plain film and have significant clinical symptom such as back pain will undergo CT scan. The sensitivity of plain radiographs is not as high as CT scan in detecting thoracolumbar spine fractures .
Cross-table lateral radiograph shows chance fracture of lumbar spine shows fanning of spinous processes (double-headed arrow) and fracture extending through pedicle (between arrowheads) and into L2 vertebral body (single-headed arrow)
The role of Multidetector CT imaging of the thoracolumbar spine for detecting chance fractures has been extensively studied. Its high resolution, particularly for osseous structures make it ideal to detect fractures in the pedidcles , delineat the extent of fracture fragments into spinal canal (ref). It also provides better visualisation of vertebral arch and facet joint comparing to plain radiograph. In a study by ( ref) demonstrated that MDCT is superior to conventional radiograph for delineating the extend of fracture fragments into spinal canal. A prospective study was conducted by Wintermar et al (Article, 21, 6) show MDCT has a sensitivity of 97-100% of thoracolumbar spine chance fracture compare to plain film with 60-70%.(art 30)
CT scan with sagittal and coronal reconstructions planes is performed routinely in the evaluation of thoracolumbar fractures. Study by Sheridan and co-workers (22) was conducted to compared the sensitivity of CT and Plain radiography in detecting chance fractures. Sagittal and coronal reconstructed views were shown to improve sensitivity for detection of lumbar fractures from 95% to 97% and of thoracic fractures from 62% to 86% (article 11). Sagittal CT reconstructed 3mm slice width and a 250 mm window level is more accurate in depicting the radiographic signs as seen on the lateral projection.
The transverse fracture through the posterior elements is more clearly seen in coronal CT 3 mm slices width and 250 window level reformations than in AP radiograph. The axial 3 mm slices width demonstrates the neural canal and the relationship of fracture fragments to the canal more clearly. (article 16,30)
MDCT has some disadvantages for instance, it uses high doses of radiation, cost effective but it is faster and highly accurate in determining the extent of fractures.
Sagittal CT reformation showing horizontal L2 Chance fracture into vertebral body and through left pedicle (arrow).
Magnetic Resonance Imaging
MRI is another modality that is considered in acute spinal trauma. This modality is only indicated when patients have a neurological deficit despite normal appearance on CT scan or plain film of the spine. MRI is used to assess the integrity of the middle column and posterior ligaments, soft tissue and spinal cord damage resulting from unstable chance fractures.
According to ( l), MRI imaging protocol of thoracolumbar spine including 4 mm thick sagittal T1 weighted , T2 weighted, STIR sagittal and T2 axial is recommended in patients with ligament injury. Sagittal T2- weighted sequences are best to demonstrate soft-tissue edema and spinal cord injury. With sagittal T1- weighted sequences are best to evaluate ligaments. Sagittal STIR is best to demonstrate fracture and bone bruise. (article 11, 8). MRI is superior in demonstrating ligamentous , spinal cord injuries and has been reported to have excellent sensitivity (100%) and specificity (95ââ‚¬"100%) ref. Study by ( ref) showed that CT have a sensitivity of 80 to 100% , while MRI have a sensitivity of 27 to 70% in detection of thoracolumbar fractures.
MRI has the distinct advantage in its ability to detect ligamentous and soft tissue injuries compared to CT. Howerver, Claustrophobia can be a real problem for the patient and is reported in 1ââ‚¬"40% of cases. (Michael Smith et al 2009). Study done by (ref), MRI is superior to CT in imaging neurological structures, the intervertebral disc and major ligaments.
Chance fracture of L1 shows marked high signal in soft tissue and interspinous ligaments (arrowheads). Bone marrow edema is seen in vertebral body and in pedicle (arrows).
The protocols for imaging a suspected chance fracture seem to in date with current best practice. Research has shown that MDCT has a 100% sensitivity and 95-100% specificity for assessment chance fractures. It is cost effective, relatively quick and but it uses high dose radiation. Therefore I conclude that CT is the most effective imaging pathway for diagnosis a suspected chance fracture, and where MSCT is not available plain radiograph should be considered.