Assessment of Thoracolumbar Spine Injuries
using Medical Imaging
Musculoskeletal injuries affecting the spine make up a notable portion of injuries worldwide. The thoracic and lumbar regions account for approximately 75% to 90% of spinal fractures, with the majority occurring at the junction between the thoracic and lumbar vertebrae (T10-L2). Although thoracolumbar fractures are quite common, there is currently no universally agreed-upon standard for categorizing and treating these types of injuries.
Functional Anatomy And Biomechanics Of Spine
The spine’s functional unit comprises two vertebrae and the connecting soft tissues, including the vertebral bodies, intervertebral discs, anterior and posterior longitudinal ligaments, and posterior elements.
The posterior ligamentous complex (PLC) functions as a tension band for the spine’s posterior region and is made up of the supraspinous ligament, interspinous ligaments, articular facet capsules, and ligamentum flavum. The ligaments and facet joints possess high tensile strength, limiting spinal flexion and counteracting rotational or torsional forces.
The intervertebral discs and vertebral bodies primarily support axial loading, and the axis of rotation lies in the anterior portion of the vertebral body. The erector spinae muscles and posterior ligament prevent compression on the vertebral bodies while at rest or in motion.
The classification of thoracolumbar spine injuries into three distinct groups is done by AO, with the basis of categorization being the mechanical forces responsible for causing such injuries:
- Type A: Compression and burst injuries occur as a result of the application of compressive force. These injuries primarily affect the vertebral body, with little to no harm to the posterior column being observed.
- Type B: Injuries are caused by a distraction or tensile force that results in an increase in the distance between adjacent vertebrae. B1 and B2 injuries involve an increase in the distance between the posterior elements, while B3 injuries involve an increase in the distance between the anterior vertebral elements. The specific type of vertebral body injury determines the subcategory of B1 and B2 injuries.
- Type C: Injuries that involve translation or rotation are caused by the application of axial torque forces. It is caused by rotational force and is often accompanied by either type A or type B fractures. “Shear” refers to a force that runs parallel to a surface, whereas “torsion” refers to a twisting force.
Type A fractures typically affect only one column, namely the anterior column, whereas type B and C fractures involve two or all three columns.
Type A: Vertebral Body Compression
The injury caused by axial compression, with or without flexion, mainly affects the vertebral body. Typical results observed on medical imaging include:
- Decrease in the height of the front portion of the vertebral body.
- A reduction in the height of the back wall of the vertebral body if it has suffered a fracture.
- A vertical split in the lamina can cause an increase in the horizontal distance between the pedicles.
- Distance between spinous processes can increase even if the posterior wall is not damaged.
However, a significant increase in interspinous distance typically suggests the presence of a posterior distraction injury. Moreover, while fracture pieces of the posterior wall may move backward into the spinal canal, there is no observable movement of these fragments in a vertical or rotational direction.
A CT scan can reveal that a displaced fragment has a clearly defined, dense, and smooth margin on the posterior side, while the margin on the anterior side is less well-defined. Type A injuries do not involve translational dislocation in the horizontal plane.
Impaction fractures classified as type A1 lead to the deformation of the vertebral body caused by the compression of cancellous bone. There is an absence of bone fragmentation. These types of fractures are characterized by an intact posterior column, and there is no narrowing of the spinal canal, which means that neurological problems are uncommon. Additionally, these fractures are considered stable. Type A1 are divided on subgroups:
- A.1.1: impaction of endplates
- A.1.2: wedge impaction fracture
- A.1.3: vertebral body collapse in osteoporotic spines
These types of injuries occur when the vertebral body is split, with the split occurring either in the sagittal plane. Type A2 are divided on subgroups:
- A.2.1: sagittal split
- A.2.2: coronal split fracture
- A.2.3: disc material entrapped within (pincer)
The burst subtype of fractures has the highest occurrence and severity among type A fractures. This subtype has further subgroups:
- A3.1: incomplete burst fractures
- A3.2: burst split burst fractures
- A3.3: complete burst fractures
Burst fractures involve either partial or complete fragmentation of the vertebral body, which leads to the outward scattering and backward displacement of bone fragments into the spinal canal. Despite the burst fracture, the posterior ligamentous complex remains intact.
Type B: Injury to Anterior and Posterior Elements with Distraction
A type B injury is characterized by a transverse disruption that results in an increase in inter-vertebral distance, either posteriorly (B1, B2) or anteriorly (B3). Type B1 and B2 injuries denote flexion-distraction injuries, while type B3 injuries indicate a hyperextension injury.
These injuries involve a disruption in the posterior longitudinal ligament and a subluxation, dislocation, or fracture of the facet joints. B1 injuries are divided into smaller groups based on specific characteristics:
- B1.1: The soft tissues, including the disc, are affected by the anterior lesion.
- B1.2: Anterior lesion involves a bone fracture, specifically a type A fracture.
There is a disruption in the posterior aspect of the bone, which involves a fracture line passing through the laminae and pedicles or isthmi.
- B2.2: The soft tissues, including the disc, are affected by the anterior lesion.
- B2.3: Anterior lesion involves a bone fracture, specifically a type A fracture.
Except for the transverse bicolumn fracture, B2 injuries generally exhibit a slightly greater severity of instability and neurological deficit than B1 injuries.
In severe cases of B1 and B2 injuries, the disruption to the posterior aspect may extend to involve not only the erector spinae muscles and fascia but also the subcutaneous tissue.
The degree of instability can range from partial to complete, and there is a noticeably greater frequency of neurological damage when compared to type A injuries.
Radiographic signs of B1 and B2 injuries include a kyphotic deformity with increased interspinous distance, anterolisthesis, bilateral subluxation, dislocation or fracture of facet joints or other posterior vertebral elements, supraspinous ligament avulsion fracture, anterior end plate shear chip fracture, or posterior edge of the vertebral body avulsion.
Unlike type A burst fractures, the CT scan of B1 and B2 injuries reveals an irregular and indistinct posterior border, as opposed to a smooth and dense anterior border. This particular feature is referred to as the “inverse cortical sign.”
The disruption in the transverse plane for a hyperextension injury commences in the anterior region and can progress posteriorly, depending on the extent of the injury. B3.1 and B3.2 injuries are typically associated with anterior displacement, while B3.3 injuries are characterized by posterior displacement.
Type C: Anterior and Posterior Element Injuries with Rotation
Type C injuries are the most severe thoracolumbar injuries, resulting in significant neurological deficits. They occur when the spinal cord is compressed by fragments or translational displacement. Features include two vertebrae rotating against each other, disruption of ligaments and discs, and various fractures. Fractures of the transverse processes indicate a rotational element in lumbar spine fractures. It’s important to identify any underlying injury even if transverse process fractures seem isolated. Axial rotation findings are common in type A or type B injuries.
Types of C Lesion
- C1 lesion: a combination of a rotational injury along with a type A lesion.
- C2 lesion: an injury of type B in combination with axial rotation.
- C3 lesion: multilevel and shear injuries
The Spine Trauma Study Group created the TLICS as a system for scoring and classifying spinal injuries. This system categorizes injuries into three categories:
- Injury Morphology
- Plc Integrity
- Involvement Of The Neuraxis
The TLICS aids in the prediction of both spinal stability and neurological status, which assists in determining the most suitable treatment options.
The TLICS employs simple anatomical descriptions based on observations made through radiography, CT, or MR imaging. Compression injuries are characterized by the reduction in height of the vertebral body or a disturbance in the endplate as seen in imaging. Less severe forms of compression injuries involve only the front part of the vertebral body, while more severe cases may result in burst fractures.
- TLICS injury morphology scoring assigns 1 point for compression injury and 2 points for burst fracture.
- Compression injuries that result in a coronal plane distortion of more than 15 degrees are given a score of 2 points in the TLICS scoring system.
- Translation injuries are classified as 3 points in TLICS and are identified by the horizontal displacement or rotation of one vertebral body in relation to another, as observed in imaging.
This type of injury is caused by rotational and shear forces, and is identified by spinous process rotation, unilateral or bilateral facet joint dislocation, and vertebral subluxation. Translational instability is seen best on lateral radiographs or sagittal CT/MR images, while coronal instability is best seen on anteroposterior radiographs and coronal CT images.
- Distraction injuries are observed through imaging techniques that show a separation in the vertical axis, and are assigned 4 points in the TLICS scoring system.
The injury can affect both the osseous elements and the supporting ligaments, either anteriorly or posteriorly, or both. If there are multiple injury types seen together, the one with the highest score is considered. In case of injuries affecting multiple levels, each injury is evaluated separately.
The PLC serves as a safeguard for the spinal column, protecting it from being subjected to extreme forces. If the PLC is damaged, surgery may be necessary to address the issue. Imaging techniques like CT and MRI are useful for identifying signs of injury to the PLC.
MRI is the preferred method because it allows for direct visualization of the ligaments. Based on imaging results such as facet joint widening, facet joint dislocation, and the discontinuation of the low-signal-intensity black stripe on sagittal T1- or T2-weighted MR images, the TLICS score categorizes the integrity of the PLC as intact, indeterminate, or disrupted.
To diagnose traumatic PLC injuries, MRI is highly accurate, with reported sensitivity and specificity rates of 91% and 100%, respectively. Edema without clear disruption can be classified as an indeterminate finding, according to the scoring system used for PLC integrity.
Determining the degree of spinal column injury is reliant on the neurologic status of the patient. The TLICS system categorizes the severity of a patient’s neurologic status into five categories based on their recovery potential.
An intact neurologic status receives 0 points, while incomplete spinal cord injury or cauda equina syndrome receive 3 points. Although imaging cannot determine a patient’s clinical neurologic status, it is recommended that MR imaging be used to evaluate any injury to the cord or nerve root.
Surgeons use the TLICS score to assess the extent of an injury and determine whether surgical or nonsurgical treatment is necessary. A TLICS score of 3 or lower generally indicates non-surgical management with brace immobilization and patient mobilization, while a score of 5 or higher warrants surgical intervention.
To guide the surgical approach, the TLICS score can be used with an anterior approach typically used for patients with incomplete spinal cord injury and anterior compression, while a posterior approach is more suitable for patients with injured PLC. A combined approach is often necessary for patients who have both a neurologic deficit and an injured PLC.
CT (MDCT) is the preferred imaging method for spinal injury in a trauma setting. Radiographs are not required before CT, and recent literature shows that MDCT is more accurate in identifying thoracolumbar injuries than plain X-rays.
CT images are taken with thin collimation and reconstructed in sagittal and coronal planes. CT is the initial modality for evaluating spinal trauma in many level I trauma centers. The main drawback of CT is its inability to identify ligamentous and spinal cord injuries
Magnetic Resonance Imaging
MRI is the preferred method for detecting soft tissue injuries such as spinal cord, intervertebral disks, and adjacent muscles. The MRI protocol for spine injuries involves using various imaging sequences, including sagittal T1W, T2W, and STIR images.
The STIR sequence can detect soft tissue injuries, while the gradient echo sequence is useful for detecting hemorrhagic contusion of the cord, which can impact prognosis. MRI can identify the location, severity, and cause of spinal cord lesions and different types of spinal cord injuries.
Additionally, MRI can predict outcomes, and patients with hemorrhagic contusion or cord transection typically have poorer neurological recovery than those with simple cord edema or non-hemorrhagic contusion.
Spinal Trauma In Children
Spinal injuries are relatively uncommon, accounting for 2% to 5% of all spine injuries, and in children, the flexibility and growth potential of the spine lead to distinctive fracture patterns. In children, the abbreviation SCIWORA refers to the condition of spinal cord injury without any visible abnormalities on radiological imaging.
New magnetic resonance (MR) imaging techniques, such as diffusion-weighted MR imaging (DWI) and diffusion tensor imaging, have the potential to aid in the prediction of the severity of spinal cord injury and the recovery of patients with SCIWORA.
Reporting Thoracolumbar Injuries
To describe the extent of a spinal injury, multiple factors such as comminution, percentage of vertebral height loss, retropulsion distance, and percentage of canal compromise can be considered. It is important to mention the degree of osseous retropulsion or canal effacement and to report the percentage of spinal canal narrowing.
One can estimate the degree of spinal canal compromise by applying a formula. The integrity of the PLC can be predicted by certain CT findings such as facet joint widening, interspinous distance widening, spinous process avulsion fracture, and vertebral body or facet subluxation or dislocation. However, if there are clinical concerns, direct assessment with MRI should be utilized.
In the radiology report of a patient, it is important to mention the status of the posterior longitudinal ligament (PLC) as either injured, intact, or indeterminate. Other injuries, such as those to the spinal cord, epidural hematoma, and injuries to the ligaments or disks, should also be documented.
To report the patient’s clinical status, the radiology report should mention potential spinal cord injury, epidural hematoma, and other ligamentous or disk injuries. Although the TLICS total score may be reported if there is clear imaging evidence of neurologic injury, it is typically not included if the patient’s clinical neurologic status is unknown.
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I am Vedant Vaksha, Fellowship trained Spine, Sports and Arthroscopic Surgeon at Complete Orthopedics. I take care of patients with ailments of the neck, back, shoulder, knee, elbow and ankle. I personally approve this content and have written most of it myself.
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