Rate dependence of hydraulic resistance in human lumbar vertebral bodies.

Abstract

Twenty-one intact human lumbar vertebral bodies (L3 and L4) were used to determine the changes in measured intraosseous pressure for 2 volumetric flow rates and to calculate hydraulic resistance in both cases. To evaluate changes in hydraulic resistance in intact vertebral bodies under different rates of flow. Hydraulic resistance has been implicated in the creation of high-speed vertebral injuries, such as burst fracture, but no previous study has measured hydraulic resistance under high-speed loading conditions. Previous work in whole bone preparations showed that hydraulic resistance was constant under low-speed conditions. The authors hypothesized that: (1) measured pressure would increase with increasing input flow rates, and (2) hydraulic resistance would remain constant at increased input flow rates. Using 2 input velocity conditions (10 mm/s and 2500 mm/s), resultant pressures were measured and hydraulic resistance calculated. Trabecular architecture was determined using micro-computerized tomography after testing. Measured pressure increased with increasing input flow rates. However, average hydraulic resistance decreased significantly when comparing low-speed (3.40 +/- 1.58kPa*s/mL) and high-speed (0.16 +/- 0.08kPa*s/mL) groups. Current hydraulic resistance results contradict previous findings. The observed decrease in hydraulic resistance suggests that, during high-speed injury events, marrow flow may damage the trabeculae and thereby weaken the vertebra.