Background: The relationship between obesity and osteoporosis is an important public health issue. The goal of this study was to investigate whether and to what extent central obesity traits affect bone mineral density (BMD). Methods: We conducted a two-sample Mendelian randomization analysis. Genomewide significant single nucleotide polymorphisms associated with waist circumference, hip circumference, waist-to-hip ratio, waist circumference adjusted by body mass index (WCadjBMI), hip circumference adjusted by BMI (HCadjBMI) and waist-to-hip ratio adjusted by BMI (WHRadjBMI) were obtained from a large-scale database containing 224,459 samples. The BMD summary dataset was obtained from a UK Biobank database including 265,627 participants. Results: The results provided strong evidence that the HCadjBMI trait was causally and negatively associated with BMD (β: − 0.135, 95% CI − 0.216 to − 0.054; P = 0.001), while the WHR trait was causally and positively associated with BMD (β: 0.194, 95% CI 0.062 to 0.325, P = 0.004). No significant effects were observed for other traits on BMD. Conclusions: This study indicates variations in the abilities of different central obesity traits to influence BMD. These results should be considered in further studies and public health measures on obesity and osteoporosis prevention strategies.

Background: For various reasons, some elderly patients with femoral neck fracture undergo delayed surgical treatment. There is little information about the effect of delayed treatment on postoperative hip function and quality of life. The aim of this study was to investigate the effect of delayed hip arthroplasty on hip function, quality of life, and satisfaction in patients with femoral neck fractures. Methods: Forty-seven patients with femoral neck fracture and hip replacement delayed over 21 days served as the delayed group (D group). Patients with femoral neck fracture, matched 1:1 for age and sex, and hip replacement within 7 days served as the control group (C group). The Harris hip score (HHS) and health-related quality of life (HRQoL) were assessed before surgery and 3 months, 6 months and 1 year postoperatively. The satisfaction questionnaires were completed by the patients themselves at the last follow-up. Results: The HHS in the C group was lower than that in the D group (32.64 ± 9.11 vs. 46.32 ± 9.88, P < 0.05) before surgery but recovered faster after surgery. The HHS in the D group was lower than that in the C group 1 year postoperatively (85.2 ± 3.80 vs. 89.8 ± 3.33, P < 0.05). The patients’ quality of life changed similarly to their HHS. The HHS 1 year after surgery was related to the preoperative HHS in group D (r_s = 0.521, P < 0.01). Patients in the D group showed significantly higher satisfaction scores than those in the C group (P < 0.05). Conclusions: Hip function in patients with femoral neck fracture surgery delayed over 21 days recovered more slowly than that in those who underwent surgery within 7 days. However, they were more satisfied with the surgery. Moderate hip movement to ameliorate the lower limb muscle atrophy was recommended for patients facing a temporary inability to undergo surgery.