Effect of short-term unloading on T2 relaxation time in the lumbar intervertebral disc--in vivo magnetic resonance imaging study at 3.0 tesla.

BACKGROUND CONTEXT: Diurnal changes in T2 values, indicative for changes in water content, have been reported in the lumbar intervertebral discs. However, data concerning short-term T2 changes are missing.

PURPOSE: The purpose of this study was to investigate the short-term effects of unloading on T2 values in lumbar intervertebral discs in vivo.

STUDY

DESIGN

Experimental study with repeated measurements of lumbar discs T2 relaxation time during a period of 38 minutes of supine posture.

PATIENT SAMPLE: Forty-one patients with acute or chronic low back pain (visual analog scale ≥3).

OUTCOME MEASURES: T2 relaxation time in the intervertebral disc, lumbar lordosis angle, and intervertebral disc height.

METHODS

Forty-one patients (mean age, 41.6 years) were investigated in the supine position using a 3-tesla magnetic resonance system. Sagittal T2 mapping was performed immediately after unloading and after a mean delay of 38 minutes. No patient movement was allowed between the measurements. One region of interest (ROI) was manually placed in both the anterior and the posterior annulus fibrosus (AF) and three ROIs in the nucleus pulposus (NP).

RESULTS

There was a statistically significant decrease in the anterior NP (-2.7 ms; p<.05) and an increase in T2 values in the posterior AF (+3.5 ms; p<.001). Discs with initially low T2 values in the NP showed minor increase in the posterior AF (+1.6 ms; p<.05), whereas a major increase in the posterior AF was found in discs with initially high T2 values in the NP (+6.8 ms; p=.001). Patients examined in the morning showed no differences, but those investigated in the afternoon showed a decrease in the anterior NP (-5.3 ms; p<.05) and an increase in the posterior AF (+7.8 ms; p=.002). No significant differences were observed in other regions. Correlation analysis showed moderate correlations between the time of investigation and T2 changes in the posterior AF (r=0.46; p=.002).

CONCLUSIONS

A shift of water from the anterior to the posterior disc regions seems to occur after unloading the lumbar spine in the supine position. The clinical relevance of these changes needs to be investigated.