An in vivo magnetic resonance imaging study of changes in the volume (and fluid content) of the lumbar intervertebral discs during a simulated diurnal load cycle

Study Design. Magnetic resonance imaging was used to measure the changes in volume of the lumbar intervertebral disc in vivo during a load cycle. Objectives. To measure changes in volume of the lumbar intervertebral disc during a load cycle and relate these changes to changes in fluid content. Summary of Background Data. There have been very few experiments conducted to measure the volume and fluid changes in intervertebral discs in vivo. Methods. Five healthy subjects were recruited (aged 27, 29, 31, 34, and 52 years) in a study using magnetic resonance imaging to measure the changes i n volume of the lumbar intervertebral disc in vivo, during a load cycle. Th e experiment was designed to simulate a diurnal load cycle, but over less t ime. The load cycle consisted of bed rest, followed by walking with a 20-kg backpack for 3 hours, followed by bedrest for 3 hours. Magnetic resonance imaging scans of the lumbar spine were obtained 10 times during this load c ycle. The disc volume was calculated by summing the disc area contained in each slice of the scan. The changes in volume of the discs (L2-L3, L3-L4, a nd L4-L5) recorded at the 10 times were then related to the fluid changes. Results. Load-induced changes in disc volume can be detected and measured u sing MR imaging. The average volume increase 3 hours after removing a highl y compressive load was 5.4%. The water content of the nucleus and anulus in the disc of the young human is said to be approximately 80% and 70%, respe ctively. If the disc gained 5.4% of its initial total volume, and assuming that the initial fluid content was approximately 75%, then it gained approx imately 7% (i.e., 5.4%/75% x 100% approximate to 7%) of its fluid. Conclusions. Load-induced changes in disc volume can be detected and measur ed using magnetic resonance imaging.