Differences in subtrochanteric and diaphyseal atypical femoral fractures in a super-aging prefectural area: YamaCAFe Study

Introduction Atypical femoral fractures (AFFs) have been correlated with long-term use of bisphosphonates (BPs), glucocorticoids (GCs), and femoral geometry. We investigated the incidence and characteristics of subtrochanteric (ST) and diaphyseal (DP) AFFs in all institutes in a super-aging prefectural area. Materials and methods We performed a blinded analysis of radiographic data in 87 patients with 98 AFFs in all institutes in Yamagata prefectural area from 2009 to 2014. Among the 98 AFFs, 57 AFFs comprising 11 ST fractures in 9 patients and 46 DP fractures in 41 patients with adequate medical records and X-rays were surveyed for time to bone healing and geometry. Results Of the 87 patients, 67 received BPs/denosumab (77%) and 10 received GCs (11%). Surgery was performed in 94 AFFs. Among 4 AFFs with conservative therapy, 3 required additional surgery. In univariate regression analyses for ST group versus DP group, male-to-female ratio was 2/7 versus 1/40, mean age at fracture was 58.2 (37–75) versus 78 (60–89) years, rheumatic diseases affected 55.5% (5/9) versus 4.9% (2/41), femoral lateral bowing angle was 1.7 (0–6) versus 11.8 (0.8–24)°, GC usage was 67% (6/9) versus 4.9% (2/41), and bone healing time was 12.1 (6–20) versus 8.1 (3–38) months ( p < 0.05). In multivariate analyses, higher male-to-female ratio, younger age, greater proportion affected by rheumatic diseases, and higher GC usage remained significant ( p < 0.05). Conclusions The incidence of AFFs in our prefectural area was 1.43 cases/100,000 persons/year. This study suggests that the onset of ST AFFs have greater correlation with the worse bone quality, vice versa, the onset of DP AFFs correlated with the bone geometry. The developmental mechanisms of AFFs may differ significantly between ST and DP fractures.