Recent studies have shown that bone modeling can occur throughout life, suggesting bone has a persistent ability of adapting structure to loading. Some bone medications have a significant effect on the process of bone modeling based on histological studies. Bisphosphonates (BP), a classical anti-resorption drug which impacts the process of bone turnover, is related with atypical femur fractures while the mechanism is unclear. Several hypotheses are considered competitive. Among them, increased femur bowing is associated with atypical femoral fractures. However, it remains doubtful whether long-term BP use increases femur bowing. Thus, the investigators design this retrospective cohort study.

If the participants meet the Inclusion Criteria, the investigators will collect the baseline characteristics of patients including age, gender, body mass index (BMI), as well as characteristics of BMD by dual-energy X-ray absorptiometry (DXA), BP treatment (type of drugs, duration before baseline). The primary outcome was femoral lateral bowing (FLB), femoral neck shaft angle (FNSA), and hip knee shaft angle (HKSA) from the frontal plane in standing radiographs of the lower limbs.

Inclusion Criteria:

• standing radiographs of the lower limb

Exclusion Criteria:

• non-standard lower limbs X-ray , rheumatoid arthritis, tumor of the femur， congenital anomalies of the lower extremity

patients are mostly from Zhejiang Province