The painful bone marrow edema syndrome of the hip joint.

In this issue of the WKW, Aigner et al have published that, for the first time, a conservative approach with iloprost has shown to be equally successful as the well-documented core decompression surgical approach in patients with BMES of the hip joint. The BME pattern on MR-imaging of the hip joint represents a common but unspecific finding, which may be associated with several diseases requiring different therapeutic strategies (Table 1). It is still controversial, whether BMES of the hip represents a distinct self-limiting disease also known as transient osteoporosis, transient marrow edema, or algodystrophy, or merely reflects a subtype of ON. Since prognosis and therapeutic consequences vary significantly, differential diagnosis between BMES, CRPS and ON is of clinical interest (Table 2). Both, BMES and ON show similar ON risk factors and a male prevalence, while classical CRPS has a history of trauma and a prevalence among females. Clinical presentation of BMES and ON is similar with typical mechanical pain and prevalence of the hip joint. In contrast, classical CRPS shows a diffuse and burning pain in combination with trophic and vasomotor signs, mainly in the hands and feet. Imaging patterns of BMES are more diffuse, across the entire femoral head, while focal and subchondral in ON. In both, the patterns are limited to the femoral head. In contrast to classical CRPS, the imaging changes are located in all periarticular bones, and the soft tissues are always affected. The histological bone marrow changes are similar in all three diseases, but with abundant new bone formation in BMES and CRPS, whereas in ON only limited new bone formation surrounds the focal necrosis with a sclerotic rim. Protected weight-bearing and treatment with iloprost for BMES, but operative treatment for ON, and a sophisticated physiotherapy for CRPS in combination with iloprost are the preferred treatment strategies in our institution.