Radiographic evaluation of the lumbosacral disc height

Objective. To establish criteria for the radiographic evaluation of narrowi ng of the L5-S1 disc height, which varies widely with transition of the L5 vertebra. Design and patients. Nondegenerated disc heights of L3-4 to L5-S1 and the t hickness and length of the L5 transverse process were measured on plain rad iographs of the lumbar spine in 166 outpatients, aged 18-35 years (mean 26. 3 years), in whom at least the L3-4 and L5-S1 discs both showed normal sign al intensity on magnetic resonance imaging. The level of the iliac crest wa s recorded semiquantitatively. The disc height was expressed as a percentag e of the L3-4 disc height, namely "relative disc height". The ratio of disc height to the sagittal diameter of the overlying vertebral body was termed the "disc height index" Results and conclusion. The relative disc height and disc height index of L 5-S1 showed strong negative correlations with two anatomic variables, which were the relative thickness of the transverse process and the level of the iliac crest (P<0.0001). The results of linear regression analysis suggest that narrowing of the L5-S1 disc height can be evaluated on plain radiograp hs alone in relation to these anatomic variables.