INTRAVERTEBRAL PRESSURE CHANGES CAUSED BY SPINAL MICROTRAUMA

CLINICAL STUDIES INDICATE variations in intravertebral pressures in pa tients with and without low back pain. It is known that not all patien ts with back pain have abnormal lumbar radiographs and, furthermore, m icrofractures of the endplate may be one of the causes in the origin o f low back pain. Consequently, this study was conducted to determine t he interrelationship between microtrauma and intraosseous pressures in the lumbar spine. Miniature pressure transducers were inserted into t he vertebral bodies and spinous processes of human cadaver spinal unit s. Radio-opaque medium was injected into the nucleus to fluoroscopical ly monitor the movement of the fluid from the disc as the preparation was loaded up to the initiation of microtrauma (before reaching the ul timate load-carrying capacity). The onset of injury was evidenced by t he microfracture of one of the two endplates and impregnation of the c ontrast medium into the spongiosa. After relaxation, another cycle of loading was applied by limiting the deflections to the maximum compres sion sustained under the intact configuration, The load, stiffness, an d energy-absorbing capacities were lower (P < 0.05) for the injured sp ecimen compared with the intact configuration. The intraosseous pressu res were higher (P < 0.05) in the vertebral body and the spinous proce ss of the vertebra where the endplate exhibited microtrauma in the inj ured cycle compared with the intact cycle. In contrast, the intraosseo us pressures in the vertebral body and the spinous process at the leve l where the endplate remained intact were not significantly different between the two cycles of loading. These findings suggest that the pre ssures at one level are not affected by the pressures caused by the on set of microtrauma at the other spinal level. Furthermore, because the pressures in the spinous process and vertebral bodies demonstrated si milar tendencies before and after microtrauma, it should be possible t o monitor the pressures in either component of the vertebra. This find ing may be clinically applicable, because it is a relatively simple pr ocedure to monitor spinous process pressures as opposed to vertebral b ody pressures in vivo.