Comparison of spinal cord ray matter and white matter softness: measurement by pipette aspiration method

Object. Although the gray matter of the spinal cord has been thought to be softer than the white matter, there is no evidence to support this belief. Because the spinal cord is extremely soft, it has been difficult to measure the mechanical properties of the gray and white matter. The modulis of elasticity of the gray and white matter were measured in situ by using a pipette aspiration method. Method. The spinal cord specimens were excised from Japanese white rabbits. Specimens were cut to display the surfaces of axial, frontal, and sagittal sections. The surfaces of the gray and white matter were aspirated using a 0.8-mm-inner-diameter glass pipette while monitoring with a video microscope, and the deformed length in the pipette was measured on a monitor. In each case the modulus of elasticity was calculated by comparing the relationship between the aspiration pressure and aspirated volume of the specimen with that determined by finite element analysis. The moduli of elasticity of the gray and white matter were 3.4 +/- 1.4 kPa (mean +/- standard deviation) and 3.4 +/- 0.9 kPa in the axial section, 3 +/- 0.3 kPa and 3.5 +/- 0.5 kPa in the frontal section, and 3.5 +/- 0.9 kPa and 2.8 +/- 0.4 kPa in the sagittal section, respectively. Conclusions. No significant difference in modulus of elasticity was shown between the gray and white matter of the spinal in sections made in various directions.