Body mass index inversely associated with bone microarchitecture quality: a systematic review and meta-analysis

Introduction: The rising prevalence of obesity forces the orthopedist to consider it in fracture risk assessment. Multiple studies have consistently demonstrated that people with obesity have increased bone mineral density (BMD). Although it appears other factors in bone strength may influence the fracture risk, including bone microarchitecture, which recently can be measured by trabecular bone score (TBS). The complex associations between TBS and BMI remain unclear, and some studies show inconsistent findings. This systematic review and meta-analysis aimed to understand whether increased BMI is associated with lower TBS by indirectly pooling all the available evidence from the published literature. Methods: A literature search was carried out using PubMed, Cochrane Library, Google Scholar and other popular journal databases using the terms "trabecular bone score", "body mass index" and the possible synonyms. We extracted the total sample, mean and standard deviation of TBS for patients within each BMI category from the selected literature. A meta-analysis was conducted using a random-effects model and inverse variant methods to synthesize the pooled effect size (mean difference) for each gender subgroup. Results: After an initial search and screening of 2399 studies, seven reports published between 2016-2019 were included (five cross-sectional, one cohort, and one randomized clinical trial). These include 2872 samples which were mostly women (2286). One thousand thirty-one samples were with normal BMI, 1124 samples were with overweight BMI, and 717 samples were with obesity. The included studies varied by age group and gender. The between-study heterogeneity with I2 index ranging 0%-76% studies in man showed higher heterogeneity. Compared with normal individuals, those with overweight and obesity had lower TBS with a mean difference of -0.02 (95% CI -0.03 to -0.01) and -0.07 (95% CI, -0.09 to -0.05), respectively. The differences were consistent across gender, although larger differences were found in men. Conclusion: Individuals with higher BMI have a lower TBS than individuals with normal BMI in a stepwise manner. It suggests that the inclusion of TBS can improve the assessment of fracture risk in obese individuals.