The systemic and local effects of an intramedullary injection of methylprednisolone acetate in growing rabbits.

Intramedullary injection of methylprednisolone acetate (Depo-Medrol) is successful in the treatment of children with unicameral cysts, but its mechanism of action remains obscure. Using a rabbit model, methylprednisolone was injected into the intramedullary canal of the left proximal tibia. Normal saline was injected into the right proximal tibia as a control. Venous blood samples following injection revealed that corticosteroid was rapidly cleared from bone. Serum methylprednisolone levels rose rapidly, giving a dose-response curve similar to that after an intramuscular injection in humans. Rabbits were killed and analyzed histologically for local changes. There was no fibroblastic proliferation, neovascularization, or other histologic change secondary to injection.