Torsion-Induced Pressure Distribution Changes in Human Intervertebral Discs

Abstract

In Brief Study Design. Biomechanical testing of human cadaveric lumbar specimens was performed to evaluate the effects of torsional torque on intradiscal pressure and disc height. Objective. Evaluate the effects of small torsion torques on intradiscal pressure and disc height in human lumbar specimens. Summary of Background Data. Nuclear depressurization in addition to an instantaneous disc height increase were found in previous porcine research when small (<2°) axial vertebral rotations were applied. If applicable to human spines, this phenomenon may support spinal manipulation for the relief of low back pain. Methods. Six human lumbar cadaveric functional spine units (FSU) were loaded in the neutral position with 600 N axial compression. Intranuclear pressure measurements were then obtained at 0, 0.5, 1.0, and 2.0 Nm of torsion. Posterior elements were removed and measurements were repeated for the disc body unit (DBU). Results. There was no statistically significant difference in nuclear pressure or intervertebral disc height with different torsion torques among or between the FSUs and DBUs. However, a disc height increase ranging from 0.13 mm to 0.16 mm occurred with the insertion of a 1.85-mm diameter pressure probe cannula. Conclusions. Small torsion torques showed no significant difference in intradiscal pressures or disc heights. This is an unlikely mechanism for the perceived benefits of spinal manipulation. Prior animal studies have shown a decrease in intradiscal pressure and increase in disc height with small torsion torques (<2°). These findings were tested in human cadaveric lumbar specimens. No significant effects on intradiscal pressure or disc height were seen with torsional torques up to 2.0 Nm.