CAN VARIATIONS IN INTERVERTEBRAL DISC HEIGHT AFFECT THE MECHANICAL FUNCTION OF THE DISC

Study Design. The finite element method was used to investigate the ef fect of variations in disc height on the mechanical behavior of the in tervertebral disc. Objectives. The effect of disc height on the mechan ical behavior of a human lumbar spine segment in terms of axial displa cement, intradiscal pressure, posterolateral disc bulge, tensile stres s in the peripheral anulus fibers, and longitudinal stress distributio n at the endplate-vertebra interface was evaluated.Summary of Backgrou nd Data. Disc height varies with individuals, disc level, abnormal con ditions, and clinical management. Methods. A three-dimensional finite element model of L2-L3 disc body unit was developed. Parametric studie s were undertaken by studying discs of three different heights: 8 mm, 10 mm, and 12 mm, whereas disc cross-sectional area, finite element me sh density, and all other parameters were kept constant. The model acc ounted for geometric nonlinearity but assumed that the material proper ties were linear. Results. Variations in disc height had a significant influence on the axial displacement, the posterolateral disc bulge, a nd the tensile stress in the peripheral anulus fibers, but the effect on the intradiscal pressure and the longitudinal stress distribution a t the endplate-vertebra interface was minimal. Conclusions. Variations in disc height may compromise the general conclusions reached from ex perimental work and analytic studies, in which geometric parameters (e specially disc height and disc cross-sectional area) are not taken int o consideration.