Biomechanics and patterns of spine injuries associated with spinal cord injury

Traumatic spinal cord injury in a stable spine

Different terminologies have been used previously to describe TSCI not associated with overt spinal instability. The term SCIWORA (Spinal Cord Injury Without Radiographic Abnormality) was proposed by in 1982 to describe TSCI occurring in children without evidence of spine injuries such as fracture or dislocation on plain radiographs or tomography. Given the inherent elasticity of the vertebral column in children, they suggest that the vertebral column can deform in flexion, hyperextension or distraction in such a way that the spinal cord can be injured without concomitant damage of the vertebral column. SCIWORA more frequently involves the cervical spinal cord because spinal mobility is greater in the cervical than the thoracic and lumbar spine. In the adult population, SCIWORA has also been used to describe TSCI associated with underlying spondylotic changes, spinal stenosis, ossification of posterior longitudinal ligament, ligamentous abnormalities, and/or traumatic disc herniation ( ; ; ; ), in the absence of fracture or dislocation. Many authors ( ; ) warn about the misapplication of the term SCIWORA in adults considering that these patients will commonly have underlying canal stenosis and significant degenerative changes—which are radiographic abnormalities per se—and instead propose the use of the term SCIWOCTET (Spinal Cord Injury Without Computed Tomography Evidence of Trauma) or SCIWORET (Spinal Cord Injury Without Radiographic Evidence of Trauma) in these patients.

For the cervical spine, proper identification of TSCI with a stable spine is important because they are typically associated with improved recovery ( ). While the presence or absence of radiographic/tomographic findings can help to understand the pathomechanism of the injury and guide treatment, the central aspect to SCIWORA, SCIWORET, and SCIWOCTET is that they usually are not associated with overt spinal instability. For these conditions, the spinal cord is at higher risk of injury either due to the altered biomechanics of the spine or to the decreased space available for the spinal cord. The current authors believe that the overarching concept for these aforementioned terms is the absence of spinal instability, and that these terms should be used with caution because they underestimate the importance of spinal trauma and biomechanics in the context of TSCI. Radiological evidence of trauma can include a wide range of findings, and should not be interpreted without consideration of the spinal stability. The authors instead propose to use the term TSCI with a stable spine in order to account for the biomechanical and surgical aspects involved in the management of TSCI. Indeed, TSCI with a stable spine does not preclude the presence of minor spinal injuries such as spinous process fractures that do not impair the clinical stability of the spine and do not require surgical stabilization.

In adults, underlying degenerative changes are usually observed, but the literature does not provide specific outcome predictors based on the evaluation of the underlying spondylosis.

Animal models repeatedly showed a strong correlation between the amount of spinal cord compression and severity of the neurological impairment. However, in adult trauma patients the correlation between cord compression observed on MRI and the neurological impairment remains unclear. Interestingly, normal aging of the spine commonly implies degenerative changes that cause reduction of the diameter of the spinal canal called spinal stenosis, especially at the cervical level. Literature does not provide specific outcome predictors based on the evaluation of the underlying spondylosis. In a population of adult low-velocity cervical trauma—CCS— found a somewhat counterintuitive association between maximal cord compression on MRI and neurological recovery.

The CCS is a common clinical syndrome observed after a cervical TSCI and is typically observed in the presence of a stable spine. It has been described initially by and is characterized by a disproportionate greater motor impairment in the upper extremities and varying degree of bladder dysfunction and sensory loss. The central cord syndrome is mainly prevalent in the elderly population with pre-existing spondylotic cervical stenosis ( ; ). The mechanism of trauma typically involves a fall from someone’s height with cervical hyperextension. During hyperextension of the cervical spine, spinal cord damage associated with the central cord syndrome results from posterior compression from inward bulging of the ligamentum flavum and from anterior compression from marginal osteophytes and/or bulging discs ( ). The greater impairment in the upper extremities results from the injury to the spinal gray matter and lateral corticospinal tracts ( ). More specifically, it is believed that the predominant involvement of the upper extremities is due to the somatotopic arrangement of the lateral corticospinal tracts, such that the medial (more central) portion of the corticospinal tract controlling upper extremity motor function sustains a greater injury than the lateral portion controlling lower extremity motor function ( ). However, this hypothesis has been challenged by different authors who observed a uniform damage to the lateral corticospinal tract, suggesting that motor fibers descending to the upper and lower extremities are interlaced ( ; ).

In a finite-element analysis, Bailly et al. suggest that the presence of hypertrophic ligamentum flavum induced specific stress and strain distributions consistent with previous histologic findings related to central cord syndrome. The presence of a disc bulging alone was not associated with such a pattern, but when combined with hypertrophic ligamentum flavum, increased the overall level of stress and strain in the lateral corticospinal tract ( Fig. 1 )