spinal cord mechanics

spinal cord injury

from spine fracture/dislocation at speeds greater than 10 ft/s or 7mps or 3ms; lumbar spine fracture at speeds greater than 25 ft/s or 17 mph or 7.5 m/s

primary SCI

occurs at moment of impact, caused by mech forces (compression/contusion/dislocation/hyperextension), results in immediate physical damage to SC tissue

secondary injury

initiated by primary, biochemical/cellular response (schema, hypoxia, inflammation, ionic imbalance (Ca2+ influx), excitotoxicity (glutamate), free radical production, apoptosis); hours to years

cadaveric SCI pros

realistic anatomy and tissue geometry, accurate vertebral cord interactions, allows direct measurement of SC deformation, compression magnitude, injury kinematics 

cadaveric SCI cons

no physiological response (no healing, infallamation, blood flow), limited sample size/high variability, ethical/logistics/cost, cannot model secondary fully

Viscous response

• Reflects how the SC responds to rate-dependent loading 

• Calculated used velocity of SC compression during impact

• Higher compression velocities → worse neurological outcomes 

• Reported alongside: max compression, max compression

Estimating SC compression

• Cadaveric cervical spine experiments w/ surrogate SC (silicone and barium sulfate), high speed x-ray imaging (1000fps), head-first exile impact simulated using drop tower (impact speed = 3.0 m/s), SC compression measured directly from x-ray image sequences, change in cord cross-section/profile during impact

Atlanto-axial dislocation

• produces greater compression; compared to hyperextension injuries, max compression @ 12 ms, compression = transient