Quantitative discomanometry: technique and reproducibility in vitro.

Quantitative discomanometry is a study of intradiscal pressure and volume measurements during the injection of fluid into an endplate-disc-endplate complex. The purpose of this article was to describe the technique of quantitative discomanometry, determine the reproducibility of the injection technique in a cadaveric thoracolumbar spine, and standardize the technique for future clinical investigations. Nineteen fresh human cadaveric thoracolumbar discs were injected using quantitative discomanometry to determine: (a) the time necessary for a disc to return to a baseline pressure-volume curve, (b) the reproducibility of the technique in vitro, (c) effects of the injection approach and position of the needle in the disc, and (d) effects of the type and length of tubing as well as gauge of spinal needle. A pressure-volume curve was obtained for each disc injection. Reproducibility was measured by nine parameters obtained from each pressure-volume curve: intrinsic pressure, leakage pressure, initial slope, slope between 0-0.1 ml, slope between 1-4 ml, pressure at 2 ml, pressure at 4 ml, maximum pressure, and volume at maximum pressure. The results demonstrated that (a) the injector apparatus was reproducible, (b) the time necessary for a disc to return to a baseline pressure-volume curve was 24 h, (c) the technique using fresh human cadaveric thoracolumbar discs was reproducible, (d) the anterior and posterolateral approaches had similar results if the needle was placed into the center of the nucleus pulposus using radiographic control, and (e) the type and length of tubing, and gauge of needle did not affect the results.