Stress fracture of the bowed femoral shaft is another cause of atypical femoral fracture in elderly Japanese: a case series.

BACKGROUND: We have studied stress fractures of the bowed femoral shaft (SBFs) among elderly Japanese for over a decade. On the other hand, severely suppressed bone turnover (SSBT) after long-term bisphosphonates (BPs) use has been considered to be one of the causes of low-energy diaphyseal femoral fractures, often called atypical femoral fractures (AFFs). Some studies have shown that BPs use for more than 5 years is associated with an increased risk of AFFs. Here, we present a report of our SBF case series experienced in the past 15 years in order to examine whether bowing deformity should be considered among the causes of AFFs.

METHODS: Subjects were 13 Japanese female patients with low-energy femoral shaft fractures. Mean age at injury was 77.0 years (range 67-88 years). All patients met the criteria of the AFFs' case definition. The first author treated 11 of the 13 patients over 8 years (2005-2012) based on the concept of SBFs. Regarding the regional characteristics of these patients, 10 were treated at 2 rural hospitals, and 3 were treated at 3 urban hospitals. Retrospectively, we assessed fracture type and location, existence of fracture on the contralateral side, bowing deformity, and duration of BPs use.

RESULTS: All 13 cases were AO/OTA type 32-A. Incomplete or previous fracture on the contralateral side was noted in 10 cases. Obvious bowing deformity of the femoral shaft was noted in 12 cases. BPs were taken in 7 cases, only 3 of which involved BPs use for more than 5 years.

CONCLUSIONS: We experienced 12 cases of low-energy femoral shaft fractures associated with bowing deformity. Six cases were not treated with BPs at all. Stress fractures associated with a femoral shaft bowing deformity do actually exist and should be recognized as another cause of AFFs.