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Radiographic evaluation of the lumbosacral disc height
H Inoue1, K Ohmori, K Miyasaka
1Department of Orthopaedic and Spinal Surgery, Nagoya Daini Red Cross Hospital, 2-9 Myoken-cho, Showa-ku, Nagoya 466-8650, Japan.
Objective:
To establish criteria for the radiographic evaluation of narrowing 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 thickness and length of the L5 transverse process were measured on plain radiographs 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 signal intensity on magnetic resonance imaging. The level of the iliac crest was recorded semiquantitatively. The disc height was expressed as a percentage 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 L5-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 radiographs alone in relation to these anatomic variables.