What is the mechanism of injury in spinal cord injury without a fracture?

Mechanism of Spinal Cord Injury Without Fracture

In spinal cord injury without fracture, the mechanism involves soft-tissue injuries including ligamentous disruption, disc herniation, epidural hematoma, and direct spinal cord contusion or compression, which occur most commonly from hyperextension forces in patients with pre-existing canal stenosis or spondylosis. 1

Primary Injury Mechanisms

Ligamentous Disruption

• Ligamentous injuries are the predominant mechanism in fracture-free spinal cord injuries, particularly involving the capsular ligaments, flavum ligaments, and posterior ligamentous complex 1, 2, 3
• The discoligamentous complex can fail under tensile forces during flexion-distraction or hyperextension mechanisms, leading to spinal instability without bony fracture 4, 5, 3
• MRI identifies ligamentous injury in 16.6% of trauma patients with negative CT scans, though the clinical significance varies 1

Disc Herniation

• Acute traumatic disc herniation occurs in 35% of cervical fracture-subluxations and can occur without associated fracture 6
• Disc herniation is most frequent with flexion-dislocation and flexion-compression mechanisms 6, 7
• Herniated disc material can directly compress the spinal cord or nerve roots, causing neurologic deficits even without bony injury 1, 6
• Vertebral disc injury is identified in 1.4% of patients with negative CT but symptomatic presentation 1

Epidural Hematoma

• Epidural hematomas can develop from venous bleeding in the epidural space following ligamentous disruption 1
• These hematomas compress the spinal cord and are identified in 1.3% of patients with negative CT scans 1

Direct Spinal Cord Injury

• Spinal cord contusion, intramedullary hemorrhage, and edema occur from direct mechanical trauma to the cord 1
• The severity includes extent of intramedullary hemorrhage, length of edema, degree of cord compression, and evidence of cord transection 1

Central Cord Syndrome: The Prototypical Non-Fracture Injury

Central cord syndrome represents the most common form of spinal cord injury without fracture, particularly in older adults 1

Mechanism

• Hyperextension injury in the context of pre-existing cervical spondylosis or congenitally narrow spinal canal 1
• Sudden compression of the spinal cord between the anterior hypertrophic disc-osteophyte complex and the posteriorly buckled ligamentum flavum 1
• Results in injury to the central portion of the spinal cord with formation of hematomyelic cavity within central gray matter 1

Clinical Pattern

• Disproportionately greater motor impairment in upper extremities compared to lower extremities 1
• Bladder dysfunction with urinary retention 1
• Varying degrees of sensory loss below the lesion level 1

Biomechanical Loading Patterns

Flexion-Distraction

• Flexion-distraction is the most injurious loading mode for ligamentous structures 2, 3
• Causes rupture of capsular and flavum ligaments with complete intervertebral disc rupture 3
• Produces compression of anterior white matter combined with distraction of posterior spinal cord 3
• Results in von Mises stress of 47-66 kPa and principal strains of 0.32-0.41 in white matter 3

Lateral Bending with Distraction

• Most critical loading mode, producing failure in most spinal components 2
• Increases stresses and strains significantly compared to other loading modes 2
• Particularly injurious to facet joints, surrounding cancellous bone, and capsular/flavum ligaments 2

Axial Loading at C3-C4

• C3-C4 injuries from axial loading are unique in their infrequency of bony fracture 7
• Commonly results in acute intervertebral disc herniation, anterior subluxation, or facet dislocation without fracture 7
• Acute disc herniations at this level are frequently associated with transient quadriplegia 7

Critical Diagnostic Considerations

MRI is mandatory for identifying soft-tissue pathology in patients with neurologic deficits and negative CT 1, 4

• CT has 98.5% sensitivity for bony injury but is significantly inferior to MRI for soft-tissue pathology 1
• MRI identifies abnormalities in 23.6% of patients with negative cervical spine CT, including ligamentous injury (16.6%), soft-tissue swelling (4.3%), vertebral disc injury (1.4%), and dural hematomas (1.3%) 1
• CT should not be considered adequate for excluding significant soft-tissue pathology in patients with signs or symptoms of spinal cord or nerve root injury 1

Clinical Pitfalls

• Isolated unstable ligamentous injury without fracture is extremely rare in the thoracolumbar spine but occurs more commonly in the cervical spine 1
• The capsular ligament is the most important structure protecting the spinal cord; its integrity should be carefully examined 3
• Approximately 25% of unconscious trauma patients have MRI abnormalities involving bone, disc, or paravertebral ligaments not visible on plain films or CT 1
• Transport delays may result in patients arriving outside the critical therapeutic window for acute interventions 1