Objective
To clarify the relationship between the morphologic changes of disc herniation and the clinical course of conservatively treated herniated lumbar disc patients.

Method
Follow-up MRIs and clinical assessments by the Visual Analogue Scale and Japanese Orthopaedic Association(JOA) Score were performed in 20 patients at a mean interval of 11.3 month.

Results
An average reduction ratio of herniation on the sagittal and axial images, were 21.4% and 20.8% respectively. The clinical features improved significantly and the degree of clinical improvement correlated with the reduction ratio of herniation, althougy 4 patients improved symptomatically despite increased or unchanged degree of herniation. Ten patients with extruded discs showed a higher reduction ratio of heniation with better clinical outcome than those with protruded discs.

Conclusion
The morphologic change verified on MRI of conservatively treated patients with a lumbar disc herniation is responsible for the clinical outcome although the anatomical factor alone is not enough to explain the outcome. The patients with extruded disc herniation shows more morphologic changes on MRI and better clinical outcomes than the patients with protruded discs.