CLINICAL STUDIES INDICATE variations in intravertebral pressures in patients with and without low back pain. It is known that not all patients with back pain have abnormal lumbar radiographs and, furthermore, microfractures of the endplate may be one of the causes in the origin of low back pain. Consequently, this study was conducted to determine the interrelationship between microtrauma and intraosseous pressures in the lumbar spine. Miniature pressure transducers were inserted into the vertebral bodies and spinous processes of human cadaver spinal units. Radio-opaque medium was injected into the nucleus to fluoroscopically monitor the movement of the fluid from the disc as the preparation was loaded up to the initiation of microtrauma (before reaching the ultimate load-carrying capacity). The onset of injury was evidenced by the microfracture of one of the two endplates and impregnation of the contrast medium into the spongiosa. After relaxation, another cycle of loading was applied by limiting the deflections to the maximum compression sustained under the intact configuration. The load, stiffness, and energy-absorbing capacities were lower (P< 0.05) for the injured specimen compared with the intact configuration. The intraosseous pressures were higher (P< 0.05) in the vertebral body and the spinous process of the vertebra where the endplate exhibited microtrauma in the injured cycle compared with the intact cycle. In contrast, the intraosseous pressures in the vertebral body and the spinous process at the level where the endplate remained intact were not significantly different between the two cycles of loading. These findings suggest that the pressures at one level are not affected by the pressures caused by the onset of microtrauma at the other spinal level. Furthermore, because the pressures in the spinous process and vertebral bodies demonstrated similar tendencies before and after microtrauma, it should be possible to monitor the pressures in either component of the vertebra. This finding may be clinically applicable, because it is a relatively simple procedure to monitor spinous process pressures as opposed to vertebral body pressures in vivo.