What evidence supports cervical spine injury in a physically active adult who landed on his buttocks while carrying a 75‑lb (≈34 kg) rucksack?

Cervical Spine Injury from Buttocks Landing with Heavy Rucksack

A fall landing on the buttocks while carrying a 75-lb rucksack can transmit significant axial loading forces through the spine to the cervical region, creating a plausible mechanism for cervical spine injury that warrants appropriate imaging evaluation based on clinical criteria.

Mechanism of Injury and Biomechanical Considerations

Axial Load Transmission

• Axial loading is a well-established mechanism of cervical spine injury, where compressive forces are transmitted along the spinal column 1
• When landing on the buttocks, the impact force travels superiorly through the lumbar and thoracic spine, ultimately reaching the cervical spine 1
• The additional 75-lb (34 kg) rucksack mass significantly amplifies the transmitted forces during deceleration, as backpack loads create proportionate increases in forces exerted on the spine 2

Load Distribution Effects

• Approximately 70% of vertical forces from backpack loads are borne by the upper back and shoulders, with 30% transferred to the lower back 2
• Heavy backpack loads (18% of body weight or greater) demonstrably alter cervical spine positioning, reducing the craniovertebral angle and increasing forward head posture 3
• The rucksack creates consistent anterior forces on the spine, which combined with axial loading during impact, can contribute to cervical injury patterns 2

Clinical Evaluation Framework

Initial Assessment Criteria

You should apply either NEXUS or Canadian C-Spine Rule (CCR) criteria to determine if imaging is indicated 4:

• NEXUS criteria have 81.2-99.6% sensitivity for detecting significant cervical spine injury 4
• CCR criteria demonstrate 100% sensitivity but with lower specificity (0.6-42.5%) 4
• If the patient meets either set of criteria (midline tenderness, altered mental status, focal neurological deficit, intoxication, or distracting injury), imaging is mandatory 4

Imaging Algorithm

For patients meeting clinical criteria for imaging:

1. CT cervical spine without contrast is the gold standard initial study 4

   • CT detects >99% of cervical spine injuries when combined with clinical assessment 4
   • Sensitivity approaches 100% for bony injuries and clinically significant fractures 4
   • Superior to plain radiographs, which detect only approximately one-third of fractures visible on CT 4

2. MRI cervical spine without contrast should be obtained if:

   • Any neurological deficit is present at examination 4
   • CT demonstrates fracture or malalignment requiring soft tissue evaluation 4
   • Patient remains obtunded and cannot be clinically cleared despite negative CT 4
   • Persistent neck pain despite negative CT in an examinable patient 4

Important Caveats

The obtunded patient presents special challenges 4:

• Approximately 1% of patients with negative cervical spine CT will have unstable ligamentous injury requiring surgical stabilization identified on MRI 4
• However, purely ligamentous cervical spine injuries are exceptionally rare (0.1-0.7% of blunt trauma victims) 4
• Most MRI-detected soft tissue injuries (>90%) are stable and do not require surgical intervention 4

Prolonged immobilization carries significant risks 4:

• Complications escalate rapidly after 48-72 hours of collar use 4
• Pressure sores, increased intracranial pressure, airway problems, ventilator-associated pneumonia, and thromboembolic events all increase with prolonged immobilization 4
• Among elderly patients with cervical spine injuries, 26.8% died during treatment, principally from respiratory complications 4

Specific Injury Patterns to Consider

Axial Loading Injuries

• The described mechanism (buttocks landing with heavy load) creates axial compression forces that can cause:
  • Burst fractures of vertebral bodies 1
  • Compression fractures 1
  • Facet injuries 1
• The cervical spine is particularly vulnerable at C4-C6 levels, which are the most common sites for both bony and spinal cord injuries in trauma 5

Athletic Injury Parallels

• While not identical, the mechanism shares similarities with athletic cervical spine injuries where axial loading occurs 6, 5
• In athletic cervical spine injuries, C4-C5 levels predominate for spinal cord lesions, with C4-C6 bony injuries most common 5
• 5-10% of patients with blunt trauma have cervical spine injury, with the cervical spine accounting for approximately 50% of all spinal injuries 7

Clinical Decision-Making

If the patient is alert, cooperative, and neurologically intact:

• Apply NEXUS or CCR criteria 4
• If criteria are not met (no midline tenderness, no neurological deficit, not intoxicated, no distracting injury), imaging is not required 4
• If criteria are met, proceed directly to CT cervical spine without contrast 4

If CT is negative but clinical suspicion remains high:

• MRI should be obtained if there is persistent neck pain or any neurological symptoms 4
• The Western Trauma Association Multi-Institutional trial demonstrated CT has 98.5% sensitivity, but a small clinically significant incidence of missed injury warrants MRI in select cases 4

Avoid flexion-extension radiographs:

• These studies are inadequate 30-95% of the time due to limited motion or poor visualization 4
• They rarely identify clinically significant instability not apparent on CT (positive predictive value as low as 0%) 4
• They carry real danger of producing neurological injury 4