QUANTIFICATION OF LUMBAR INTRADISCAL DEFORMATION DURING FLEXION AND EXTENSION, BY MATHEMATICAL-ANALYSIS OF MAGNETIC-RESONANCE-IMAGING PIXELINTENSITY PROFILES

Study Design. A magnetic resonance imaging study of the internal kinem atic response of normal lumbar intervertebral discs to non-weight-bear ing flexion and extension. Objectives, To quantify the pattern of magn etic resonance imaging pixel intensity variation across discs, and non invasively monitor displacement of the nucleus pulposus during sagitta l-plane movements. Summary of Background Data, Invasive techniques use d to study intradiscal movements of the nucleus pulposus have suggeste d that it moves posteriorly during flexion and anteriorly during exten sion. A noninvasive study based on magnetic resonance images gave simi lar results for normal young women. Quantification has been problemati c, and the invasive procedures may have altered disc dynamics. Methods . Ten male subjects (age, 21-38 years) with healthy backs were positio ned in a magnetic resonance imaging portal with their lumbar spine sta bilized in flexion and extension by supporting pads. For each disc, a T2-weighted image was obtained, as was a computer-generated profile of pixel intensities along a horizontal mid-discal transect. Mathematica l curve-fitting regression analysis was used to characterize the shape of the intensity profile and to compute the point of maximum pixel in tensity. Results. A single equation fitted the profile for all normal discs. The intensity peak shifted posteriorly during flexion, anterior ly during extension. Conclusions, Automated mathematical modeling of m agnetic resonance imaging pixel data can be used to describe the funda mental shape of the pixel intensity profile across a normal lumbar dis c, to determine the precise location of the site of maximum pixel inte nsity, and to measure the movement of this peak with flexion and exten sion. This technique may be of value in recognizing incipient degenera tive changes in lumbar discs.