Correlation of microtrauma in the lumbar spine with intraosseous pressures

This study was conducted to determine the relationship between intraosseous pressure and vertebral microtrauma in the lumbar spine. Functional spinal units were excised from human cadavers. Radio-opaque dye was injected into the nucleus. Miniature transducers were inserted into the vertebrae to record intraosseous pressures. Compressive loading was applied quasistatically (2 mm/sec) until injury occurred. Movement of the contrast medium was monitored under fluoroscopy. The subchondral endplate was the most vulnerable component for initiation of injury to the lumbar spine segment. In the initial stages of loading, the vertebral endplates gradually bulged outward, with the contrast medium staying within the nucleus. However, at higher physiologic load levels, before reaching the limiting load, the deformations increased, resulting in buckling of one of the endplates. This was followed by the contrast medium impregnating the spongiosa. Microlevel trauma was not observed radiographically after load removal, indicating that one cannot always equate a normal radiograph with normal spinal anatomy. Mean forces, deformations, stiffnesses, energies, and strains were 7.8 kN (+/- 1.4), 5.23 mm (+/- 0.78), 1940 N/mm (+/- 226), 18.7 J (+/- 4.4), and 35.5% (+/- 3.7), respectively. Pressure in the vertebral body containing the injured endplate before the onset of microtrauma was different (P < 0.05) from the pressure after injury; the pressures in the body containing the intact endplate, however, were not statistically different. Significant differences (P < 0.05) in the intraosseous pressures occurred between the two spinal levels at low-level physiologic loads before the onset of microtrauma.(ABSTRACT TRUNCATED AT 250 WORDS)