Study design: In a laboratory study, 21 human lumbar spine segments were used to determine whether intraosseous pressure increases occur during axial-compressive loading conditions under two displacement rates.
Objective: To determine whether an intraosseous pressure rise is associated with burst fracture formation.
Summary of background data: Burst fractures are high-speed injuries usually associated with neurologic deficit. An internal pressure rise has been implicated as a critical factor in burst fracture formation. The authors hypothesize that the internal pressure increases with increasing input velocity.
Methods: The internal pressure changes were measured in spine segments using two displacement rates: 10 mm/s (slow speed) and 2500 mm/s (high speed). Failure load and energy absorption were determined for both groups. The resultant fracture types were determined from postinjury radiographs.
Results: The initial peak internal pressure decreased from slow- to high-speed tests (P < 0.01). Overall peak pressure, failure load, and energy absorbed at failure were not significantly different. Slow-speed tests resulted in compression fractures, whereas high-speed tests resulted in burst and compression fractures.
Conclusions: The current research did not support the current theory of burst fracture formation. There was a decrease in measured internal pressure from the slow- to high-speed groups, and burst fractures still were produced. The theory could be potentially modified to suggest that the nucleus entering the vertebral body acts as a wedge, splitting the vertebral body apart and enabling the bony fragments to be pushed into the canal space.