[Femoral osteonecrosis - Ahlbaeck's disease]

Osteonecrosis of the knee can present as a spontaneous, primary (SPON) or a secondary clinical entity (SON). The natural history of SPON follows a course of several sequential stages which seem to be irreversible in later stages of both entities. Early diagnosis of ON is crucial and the earlier the stage of the lesion at the time of diagnosis, the better the prognosis. Clinically, early diagnosis and treatment of ON might prevent unnecessary surgery in cases with a concomitant degenerative meniscal tear. From a medicolegal viewpoint early-stage ON should be ruled out prior to surgery as arthroscopy has recently been associated with ON. Recent biopsy studies showed that SPONK is most likely caused by insufficiency fractures which seem to appear as osteonecrotic lesions in later stages of the disease due to failed bone healing.