INTRODUCTION: Disc height narrowing is the most commonly used specific finding to indicate intervertebral disc (IVD) degeneration. To date, reports of cohort study on the changes of disc height is rare. The purpose of this study was (1) to quantitatively evaluate the change of lumbar disc height by radiographic measurement, and (2) to investigate risk factors for the development of disc height narrowing in a population‐based retrospective cohort study.
METHODS: During ten years from 1997 to 2007 (total six times medical examinations in typical mountain village in Mie, Japan), the inhabitants who participated in the examination more than four times (59 men, 125 women, mean age: 70.1 [61‐83]) were subject of this study. Lateral lumbar spine radiographs of each subject were taken, and digitally scanned, and then disc height (L1/2 to L5/S1) was measured. According to the rate of change in the disc height, the subjects were divided into two groups as follow: mildly decreased group (less than 20% decrease) and severely decreased group (more than 20% decrease). The stepwise multiple logistic regression analysis was used to select factors significantly associated with disc height narrowing.
RESULTS: Changes in Disc Height: Disc height of each IVD level showed gradual decrease during ten years. The rate of changes in the disc height did not differ significantly among the IVD levels during study period (p = 0.78). Factor Analysis: female and treatment history of hypertension were associated with an increase risk of disc height narrowing, whereas BMI and disc height (L5/S1 level) at baseline were associated with a reduction in the risk of disc height narrowing.
DISCUSSION: This is the first population‐based cohort study that quantitatively evaluated the IVD height for ten years. The results indicate that the female and hypertension are significant risk factors for the development of lumbar disc height narrowing.