Spinal Trauma & Spinal Cord Injury: General Principles
Injuries to the spine – the vertebral bodies, their surrounding soft tissues, and the spinal cord itself – can cause devastating neurological consequences. Rapid evaluation of any patient with potential spinal trauma is crucial to rule out damage to the spinal cord and nerve roots. Even without neurological involvement, spinal injuries can be very painful and possibly disabling. In this section, the general principles of spinal trauma will be presented. A selection of more specific traumatic spinal conditions will be discussed in a separate chapter.
Structure and Function
The spinal column is divided into four main parts: cervical, thoracic, lumbar, and sacral (Figure 1). Twenty-four vertebral bodies (7 cervical, 12 thoracic, 5 lumbar) extend from the foramen magnum at the skull to the sacrum at the pelvis.
The first cervical vertebra (C1) is known as the atlas, and the second (C2) is known as the axis. The atlas articulates with the occiput of the head above and the axis below. The morphology of the atlas and the axis differ markedly from the other vertebrae below them. The atlas has no vertebral body and no spinous process. Rather, there are lateral masses connected by anterior and posterior arches. The C2 vertebra has an odontoid process (also known as the dens) which is a peg or protuberance that enters the C1 body, creating the atlanto-axial joint for rotation of the head (see Figure 2).
The vertebral bodies are draped front and back by the anterior and posterior longitudinal ligaments, respectively. The ligamentum flavum covers the posterior aspect of the spinal canal and connects the lamina while the interspinal and intertransverse ligaments connect the spinous processes and transverse processes of adjacent vertebrae, respectively. Discs are situated between each vertebral body to act as cushions.
The spinal cord travels through the spinal canal from the foramen magnum to (approximately) the caudal aspect of the L1 vertebral body. It is bordered in the front by the vertebral bodies, to the sides by the pedicles, and to the back by the laminae.
At each vertebral level, the dorsal and ventral rami come together to create the nerve roots, which exit the spine through the lateral foramen.
At that point, the cord forms the conus medullaris and gives off a collection of nerve roots called the cauda equina (as this collection is said to resemble a horse’s tail). These peripheral nerves travel through the spinal canal until their point of exit at a neural foramen. In the cervical spine, the vertebral arteries pass through the transverse foramina before entering the foramen magnum.
Different portions of the spinal column have different propensities for injury. Most of the thoracic spine down to T10, for example, is relatively protected during trauma by its articulation with the inherently stable rib cage. On the other hand, the thoracolumbar region (T11-L2) has more flexibility and mobility, which enhances its daily utility, but makes the region more prone to injury in trauma. Likewise, at each of the junctions between regions –occipitocervical, cervicothoracic, thoracolumbar, and lumbosacral– mobility is maximized at the cost of stability.
Spinal trauma has a bimodal age distribution. Younger patients typically present after high-energy trauma such as motor vehicle collisions. Geriatric patients are injured by low-energy mechanisms such as falls in the setting of osteoporosis and degenerative changes in the spine.
There are approximately one million spinal fractures each year in the US. Of those, approximately 75% involve the thoracolumbar spine. Spinal cord injuries occur far less frequently, with about 10,000 new cases per year. Approximately half of these cases involve the cervical region, with the remaining half divided between the thoracic or lumbar regions. The level of function after spinal cord injury can be assessed on physical examination by motor and sensory testing (see Tables 1 and 2) and is more commonly assessed using the American Spinal InjuryAssociation (ASIA)scoring system (see Figure 3).
As a rule, the higher the level of injury, the greater the functional loss. If the functional injury is at the C6 level, wrist extension and supination are intact; thus, patients can often feed themselves. When C7 function is retained, patients can power a manual wheelchair or perform transfers from chair to bed, since they have persevered triceps function. T1 level function, which powers the hand intrinsic muscles, is needed to have full manual dexterity. Injuries in the lumbar spine cause lower extremity dysfunction and urinary/fecal continence.
Cord injury can further be categorized as complete or incomplete.
Incomplete injury leads to some measure of voluntary distal motor and/or
perianal sensation. Neurological impairment can be classified using the
American Spinal Injury Association Impairment Scale
(see Table 3). Complete spinal cord
injury can only be defined once the patient is
no longer in spinal shock, a point defined by the return of the
normal bulbocavernosus reflex arc.
In cases of incomplete spinal cord damage, symptoms will vary based on the portion of the cord affected.
Central cord syndrome is the most common incomplete spinal cord injury syndrome. Central cord syndrome is most frequently seen after a fall in elderly patients who have a history of cervical spondylosis or spinal stenosis. Central cord syndrome results from a spinal cord contusion usually caused by hyperextension of the cervical spine. This contusion causes axonal disruption of the lateral columns selectively. Central cord syndrome affects fine motor control of the hands but may be seen distally as well, including loss of bladder control.
Anterior cord syndrome is characterized by complete motor paralysis and loss of temperature and pain perception distal to the lesion. Since posterior columns are spared, light touch, vibration, and proprioceptive input (sensation) are preserved. Anterior cord syndrome is caused either by direct compression or indirect injury to the anterior spinal artery. The region affected includes the descending corticospinal tract, ascending spinothalamic tract, and autonomic fibers. It is characterized by a corresponding loss of motor function, loss of pain and temperature sensation, and hypotension. This incomplete spinal cord syndrome has the worst prognosis, as only about 15% of patients regain motor function in recovery.
Brown-Séquard Syndrome is seen after damage to one side of the spinal cord, left or right, usually after penetrating trauma. It is associated with loss of function or impaired function on the side of the injury and altered pain and temperature loss on the opposite side of the injury. Among the incomplete spinal cord syndromes, Brown-Séquard has the best prognosis for functional recovery.
In any suspected spinal trauma, radiographic imaging is crucial. In most cases, CT scanning will be indicated for detailed assessment of the bony anatomy. MRI provides additional details about the spinal cord and surrounding soft tissues. In general, both studies are usually warranted. CT scans provide bony detail, and MRI provides information about the spinal cord and soft tissues.
A whole spine radiograph should be obtained to evaluate for any vertebral fractures. In the cervical spine, there are four parallel lines that should be assessed (see Figure 4). The anterior and posterior vertebral lines lie at the margin of the vertebral bodies front and back, respectively. The spinolaminar line defines the posterior margin of the spinal canal, and the posterior spinous line abuts the tips of the spinous processes. These lines should be smooth. Any so-called “step-off” is suspicious for ligamentous injury.
For suspected instability of the cervical spine, patients who can move their heads on their own may have radiographs made in flexion/extension (see Figure 5) to assess stability.
The open mouth view allows assessment of the odontoid process of C2 (see Figure 6).
Although x-rays have been historically important, CT scans have replaced x-rays over the last two decades for the evaluation of bony injuries, given their higher resolution and sensitivity. CT scanning will detect most fractures (Figures 7 and 8). CT can also help evaluate the patency of the spinal canal, although direct visualization of the spinal cord is still poor.
The main indications of MRI (see Figures 9 and 10) in spinal trauma include the following:
- X-ray or CT scan findings suggestive of ligamentous injury (e.g., spondylolisthesis or asymmetric disc space widening)
- Concern for epidural hematoma, disc herniation or occult fracture
- Suspected spinal cord abnormalities
- Suspected cervical instability in trauma patients who are obtunded or otherwise unable to pose for flexion/extension radiographs
- Neurological deficit detected on clinical examination.
Non-operative treatment of spinal trauma often centers on immobilization. Various immobilization devices can be used (see Figures 11 and 12), including a Philadelphia collar, a thoraco-lumbosacral orthosis, a lumbosacral corset, or a halo vest.
Surgery for spinal trauma (see Figure 13), in general, consists of decompressing the spinal cord (that is, relieving any pressure on it) and stabilizing the spine, usually by a spinal fusion with plates, screws, wires or rods. The construct can be supplemented with bone graft.
Spinal trauma leading to spinal cord damage will require immediate administration of certain medications. These include prophylaxis for deep vein thrombosis and fluids or vasopressors to treat or prevent shock. Administration of steroids in an attempt to reduce spinal cord edema is controversial, especially in the setting of conditions such as poly-trauma or open fractures, where the risk infection is elevated. According to a meta-analysis in the journal Neurology published in 2019, high-dose methylprednisolone early after acute spinal cord injury “does not contribute to better neurologic recoveries but may increase the risk of adverse events.”