Persistent femoral neck cysts in healed Legg-Perthes' disease: a clue to the etiology of simple bone cyst?

Persistent femoral neck cysts in an adult with healed Legg-Perthes disease had the radiological features of which are rather like those of simple bone cyst. To the author's knowledge such persistent cysts have not been reported previously. Existence of such cysts in healed Legg-Perthes' disease may provide a clue to the etiology of simple bone cyst.