Solitary bone cyst of the humerus treated by trepanation was reported. The technique consisted of drainage of the cyst fluid and multiple drilling with a kirschner wire. Four cases with the disease were treated by this method. Three of them were completely healed on follow up, and one case necessitated another treatment because of recurrence of the lesion. Biochemical analysis of the cyst fluid revealed an existence of bone resorption factors of prostaglandin E2 and Interleukin 1. Therefore, drainage seemed to be useful both for the reduction of the internal pressure of cysts and for the removal of the bone resorption factors.
