Magnetic resonance imaging of normal lumbar intervertebral discs.

OBJECTIVE To study changes in midpoint lumbar disc heights in an asymptomatic Jordanian sample relative to age, sex, lumbar level and midvertebral heights. METHODS A total of 153 asymptomatic patients (87 males, age range 20-65 years; mean 43+/-12.1 and 66 females, age range 22-68 years; mean 47+/-13.7) were selected during the study period. All underwent midsagittal magnetic resonance imaging to measure the midpoint disc height and midvertebral height of all lumbar spines. Values were statistically analyzed to obtain the significance of differences in the means of midpoint disc heights at different levels in every age group and among other age groups. The relative height indices for every lumbar level in each age group for both males and females were determined. RESULTS The results showed that a highly significant sex-independent cephalocaudal increase sequence of midpoint disc heights is evident, where maximum values are reached at lumbar 3/4 level in the younger age groups and at lumbar 5/sacral 1 level in older ones. In relation to age, midpoint disc heights displayed a non-linear, alternating increase/decrease pattern, which was of higher magnitude and statistically significant in males, but less evident and statistically insignificant in females. Maximum values were reached during the 6th decade in males while during the 5th decade in females. The relative height indices were similar in both sexes and remained fairly constant between age groups at all levels. CONCLUSION The craniocaudal and age-dependent patterns could be termed physiological and interpreted as adaptation of the lumbar spine to changing functional demands. The utility of the relative height index is discussed.