Objective
To determine the changes of posterior bulging of the lumbar intervertebral discs with flexion and extension movement of the spine in patients with central disc bulges or disc degeneration.

Method
Twenty patients with low back pain were studied. Nine patients had central type disc bulging and eleven patients had disc degeneration only. The spines were scanned in neutral, flexion, and extension positions in a vertically open 0.5T MR scanner. Degree of posterior bulging of the lumbar intervertebral disc of the pathological level was measured.

Results
In the patients with disc bulge, posterior bulging of the disc decreased in all of the patients by 0.8⁑0.6 mm with flexion of the spine and increased in 77.8% of the patients by 1.0⁑0.8 mm with extension of the spine. In the patients with disc degeneration, posterior bulging decreased with flexion in 36.7% of the patients. With extension, posterior bulging increased in 55.6% of the patients.

Conclusion
This study found that patients with low back pain and central disc bulges have consistent and marked discrepancies in posterior bulging with flexion-extension in comparison with our previous study with asymptomatic patients with normal MRIs.