Spinal cord injury is any damage or harm to the spinal cord or to the nerves arising from the cord that may lead to temporary or permanent change in function
Epidemiology of Spinal and Spinal Cord Trauma
Represents an occurrence of 27-47 cases per million people in the population per year.
Road traffic accidents are the leading causes of spinal cord injuries, and the cervical spine is the most common area of injury representing 50% of the cases, and the remainder of the cases are distributed between thoracic, lumbar, and sacral spinal injuries.
Classification of Vertebral Fractures
Before we discuss the different indications and findings on imaging studies of the spine and the spinal cord, it is important to define the main types of vertebral fractures one might face during their trauma-care rotation.
Osteoporotic fractures can present as a wedge, concave or biconcave, or a crush fracture. A wedge fracture involves the anterior vertebral body. A concave or biconcave fracture usually involves the central part of the vertebra. Finally, a crush fracture involves the anterior, central and posterior elements of the vertebral body.
Loss of the vertebral height is an important indicator of the severity of the osteoporotic fracture.
- Grade I fractures usually have a preserved vertebral body height of more than 75% of the normal vertebral height.
- Grade II fractures have a vertebral body height between 50–75% of the normal height.
- Grade III fractures have more than 50% loss of the normal vertebral body height.
Spinal canal deformity
These previous classifications are based on the morphology of the involved vertebra. Another important classification is based on the presence of spinal canal deformity due to free fragments entrapment for instance. This can be excluded by a multi-detector computerized tomography (MDCT) scan of the spine. Sagittal magnetic resonance images of the spinal cord are also useful in the evaluation of the involvement of the spinal cord.
Classification based on the mechanism of the injury
The mechanism of injury can be also used as a classifier in vertebral fractures as either:
- Flexion-compression injuries are more likely to cause a wedge fracture.
- Axial-compression mechanism of injury, such as falling vertically from a height, is more likely to cause a burst fracture or a crush fracture.
- Other mechanisms of injury, such as rotational fracture-dislocation, usually cause posterior and middle vertebral body injury with little injury to the anterior column.
Classification based on the level of neurological impairment as per the ASIA classification:
- Total loss of motor and sensory function.
- Loss of motor function only.
- Present sensory function and present of less than useful motor function (< grade 3/5).
- Present of sensory function and presence of abnormal but useful motor function (>/= 3/5).
- Intact neurological functions.
Specific spinal cord injuries may include:
- Special injuries of the upper cervical vertebra: 1) Craniocervical dislocation, and 2) Atlantoaxial instability.
- Occipital condyle fracture. It is mainly associated with accompanying head injuries.
- Jefferson’s fracture. Represents a burst fracture of the C1 ring.
- Odontoid fractures. They can be type I, II or III depending on the extent of the fracture line.
Other special fractures include:
- Wedge fractures: This refers to compression of a vertebral body either laterally or anteriorly forcing it to take the shape of a wedge.
- Hangman’s fracture: This is a fracture of both pedicles of the C2 vertebra. It depicts the pathophysiology behind death in hanging where fracture of this vertebra leads to compression of the spine at a high level an inhibition of respiratory function as well as allowing for mechanical compression of the airway.
- Burst fracture.
- Tear drop fracture.
- Facet dislocation.
Imaging of the Spine and Spinal Cord in the Traumatic Patient
Whenever a patient presents to the emergency department with a mechanism of injury suggestive of possible spinal column or spinal cord injury, one should determine the appropriate imaging modality and the likelihood of spinal cord injury. The goal of imaging of the spine in the traumatic patient is to decide whether a decompression surgery is needed or not.
- The best imaging modality to exclude spinal column injuries is multi-detector computer tomography (MDCT).
- Magnetic resonance imaging (MRI) is the modality of choice to exclude early spinal cord injury.
- Plain X-ray radiographs might be used for screening purposes, but they cannot exclude spinal cord or vertebral injuries in a high-risk patient.
X-ray Radiography and Spinal Trauma
The main goal of obtaining an X-ray of the spine is to exclude a major spinal deformity. Spinal fractures might be seen on a plain radiography, but the exclusion of vertebral body fractures should not be based on plain X-ray films alone.
A very important question here is when one should obtain an X-ray of the spine in the trauma patient.
Patients who meet the following criteria should get a spinal X-ray during their survey:
- Those with severe back pain after blunt traumatic injury,
- Those who have fallen from a height of 10 feet or more,
- Those who have been ejected from a motorcycle or motor vehicle accident at 50 miles per hour or more,
- Those with a Glasgow coma scale of 8 or less, and
- Patients with focal neurological deficits.
The issue with plain non-specific X-ray radiography is that it usually under-estimates the number and severity of spinal and spinal cord injuries; therefore, the Canadian C Rules (CCR) were developed to determine whether the patient needs specific spinal imaging or not. Patients who have a Glasgow coma scale of 15 are screened for the possibility of C-spine trauma using the CCR questionnaire.
No radiography needed
Patients who are younger than 65 years of age, who have not been involved in a dangerous mechanism of injury, who do not have focal neurological deficits, who are in the sitting position in the emergency department, have been ambulatory at any time during their visit to the emergency department, who do not have midline C-spine tenderness and who can rotate their neck to the left and right, do not need any specific cervical spinal radiography.
On the other hand, patients who are older than 65 years of age, who were involved in a dangerous mechanism of injury, or have focal neurological deficits, should get a C-spine radiograph to exclude cervical spinal injuries.
If the patient cannot sit in the emergency department, was not ambulatory at any time during his or her visit, and has midline C-spine tenderness, he or she should also get a C-spine radiograph.
Patients who meet the following criteria should get MDCT:
- Those with a Glasgow coma scale below 15,
- Those who are younger than 16 years of age,
- Those with unstable vital signs, or
- Those with acute paralysis.
It should also be noted that these screening questionnaires are put in place only to save resources in a resource-limited setting. If MDCT is readily available, then the imaging modality of choice in any patient who meets the CCR criteria should get a MDCT and not a plain radiography of the C-spine.
MDCT and Spinal Trauma
The detection rate of MDCT of cervical spinal fractures is 100%. Unfortunately, the detection rate of cervical ligamentous injuries by MDCT is not good. The main advantage of MDCT over plain radiography is the much faster clearance of the cervical spine by the former technique.
MDCT cannot provide any evidence for spinal cord injury; therefore, MDCT is usually used for the assessment and exclusion of the bony part of the spine. Magnetic resonance imaging is much more superior in evaluating spinal cord injuries.
Magnetic Resonance Imaging and Spinal Cord Injury
The main purpose of obtaining a magnetic resonance imaging study of the spine in a traumatic patient is to exclude spinal cord injury. MR imaging has an excellent detection rate of soft tissue injuries, such as pure spinal ligamentous injury, which are almost impossible to detect on an MDCT study.
Sagittal T1, sagittal gradient recalled T2, and sagittal STIR images of the spine are obtained in patients suspected to have pure spinal ligamentous injuries. Fat-suppressed T2 images also provide excellent quality images for the detection of spinal ligamentous injuries on MR imaging.
The main MR imaging finding in spinal ligamentous injury is ligamentous edema. MR findings of spinal cord injury include:
- Intramedullary hemorrhage,
- Spinal cord contusion,
- Compression by a bony fragment, or
- An acute traumatic disk herniation.
The degree of spinal cord injury, i.e., incomplete versus complete, has a huge implication on whether urgent decompressive surgery is needed. Additionally, MR imaging findings of spinal cord injuries have an impact on the prognosis of the patient.
Patients with intramedullary hemorrhage or spinal cord transection usually have a grim neurological prognosis and a very slim chance of any neurological improvement even in the long-term. On the other hand, patients with spinal cord contusions or local edema usually recover significantly if properly treated.
Diffusion-weighted MR images of the spine are very promising in the detection of subtle spinal cord injuries that are otherwise invisible on conventional MR images.
Stability of the Spinal Fracture
A very important question to the neurosurgeon is whether the identified fracture is stable or unstable. The risk of subsequent neurological injury in a patient with an unstable vertebral fracture is very high; therefore, early surgical intervention is indicated.
The vertebral body is usually classified into three columns, anterior, middle and posterior. When the fracture involves two or more columns, the fracture is considered unstable. Patients with unstable fractures on MDCT should undergo a magnetic resonance imaging study to exclude spinal cord injury and obtain baseline images for future reference.
Is the Fracture Old?
Another important question that is more challenging in an old osteoporotic woman is whether the identified fracture on MDCT is old or new. Plain radiographs are useless in answering that question. Peri-vertebral hemorrhage and spinal epidural hemorrhage, both can be assessed with MDCT or MR imaging, are useful signs suggestive of an acute new fracture rather than an old one.
Compression Vertebral Fractures: Benign or Malignant Etiology?
When a fracture is identified in the vertebral body, another very important question is raised. Is this fracture caused by a benign process, i.e., osteoporosis, or a malignant etiology? MDCT and plain radiographs cannot differentiate between benign and malignant fractures. MR imaging might be helpful in differentiating the two.
The following are MR imaging findings suggestive of a benign compression vertebral fracture:
- Low-signal-intensity band on T1- and T2-weighted images,
- Normal bone marrow signal,
- Retropulsion of a posterior bone fragment and
- The presence of multiple compression fractures.
Diffusion-weighted MR imaging is also helpful in differentiating benign from malignant fractures. Benign acute fractures usually have an increased signal on diffusion-weighted MR imaging due to bone marrow edema. On the other hand, malignant fractures usually show a low-signal.