Objective
To observe histological changes of the intervertebral disc injected with intradiscal steroid and mollification of discogenic pain.

Method
A study group of 25 Sprague-Dawely rats was divided into five subgroups. A control group of 10 Sprague-Dawely rats was divided into five subgroups. The rats' intervertebral discs were exposed by an anterior surgical approach. For study group, the rats were injected intradiscally methylprednisolone acetate 4 mg (Depomedrol, 40 mg/ml) to the L4-L5 intervertebral disc, methylprednisolone sodium succinate 4 mg (Solumedrol, 40 mg/ml) to the L5-L6 intervertebral disc, and triamcinolone acetonide 4 mg (Triamcinolone, 40 mg/ml) to the L6-S1 intervertebral disc. For control group, the rats were injected intradiscally 0.1 ml of saline to the L5-L6 intervertebral disc and a needle was inserted in the L6-S1 intervertebral disc. The intervertebral discs were extracted after 1 week, 2 weeks, 3 weeks, 4 weeks, and 16 weeks. The extracted intervertebral discs were stained with Hematoxylin-Eosin and examined histomorphometrically.

Results
There is no significant histological change in either group until 4 weeks after the different types of steroid were injected. Focal fibrotic change was present in the Solumedrol and Triamcinolone injection subgroups after 16 weeks.

Conclusion
We concluded that rapid mollification of discogenic pain following intradiscal steroid injection may not result from histological change of the disc. Further biochemical study will be neccessary to clarify mollification mechanism of discogenic pain by intradiscal steroid injection.