Measurement of in vivo intradiscal pressure in healthy thoracic intervertebral discs

Study Design. In vivo pressures were measured in radiologically healthy middle and lower thoracic discs in 6 adult volunteers. Objectives. To quantify and compare intradiscal pressures from the middle and lower thoracic spine during various body positions and maneuvers, and to investigate the potential variation of these pressures with orientation of the measurement transducer. Summary of Background Data. In vivo intradiscal pressures have been reported for the lumbar spine; however, the authors are unaware of any studies presenting intradiscal pressures in the thoracic spine. Methods. A specially constructed pressure-sensing needle was inserted into the nucleus pulposa, and pressures were recorded during a variety of body positions and maneuvers in middle and lower thoracic discs in 6 study participants. In three of the body positions, pressures were measured with the needle in both vertical and horizontal orientations to investigate whether the measured pressures were directionally dependent. Results. Intradiscal pressure varied significantly with body position and maneuver, with pressures being greatest in positions where study participants held 10-kg weights in each hand. Disc level and orientation of the pressure needle did not significantly influence intradiscal pressure. In some body positions, thoracic intradiscal pressures were significantly different from previously reported pressures from the lumbar spine. Conclusions. Thoracic intradiscal pressure was significantly influenced by body position and maneuver but not disc level. Intradiscal pressures are useful for gaining greater insight into the biomechanics of the thoracic spine.