Diurnal changes in lumbar intervertebral distance, measured using ultrasound

Study Design. This study measured the distances between the tips of the transverse processes of adjacent lumbar vertebrae (L1-L4) in the same subjects after 1 day of normal activities and again the next morning. Objectives. To determine the feasibility of directly measuring the lumbar intervertebral distance using ultrasound and to determine the magnitude of the diurnal change in the intervertebral distance. Summary of Background Data. A diurnal variation in height results from, in part, a decrease in height of the intervertebral discs with loading of the spine during the day. Previous estimates of the diurnal changes in disc height have used radiologic, stereophotographic, and magnetic resonance imaging techniques. No previous study has used ultrasound imaging. Methods. Ultrasound was used to measure the distance between the tips of adjacent lumbar vertebral transverse processes. Measurements were made on six occasions in each of seven subjects after 6:00 PM in the evening and again the following morning before rising. Results. The distance between the tips of adjacent transverse processes could be measured, within an individual, with a reproducibility of better than +/- 7.5% coefficient of variation. Reproducibility of the measurement of the total distance between L1 and L4 was better than +/- 4%. The intervertebral distances between L1 and L4 were significantly greater in the morning than in the evening. The average diurnal change in the total intervertebral distance L1-L4 was 5.3 mm. Conclusions. The study confirms the feasibility of using ultrasound to directly measure changes in the distances between the lumbar vertebrae.