Regional adipose tissue redistribution and infiltration in primary osteoporosis: A comprehensive body composition study.

backgroundPrimary osteoporosis (OP) has traditionally been viewed as a skeletal disorder; however, its complex interactions with muscle and adipose tissue are increasingly recognized. Nevertheless, the specific characteristics of body composition alterations in OP, particularly regional distribution and qualitative changes, and their independent roles remain poorly defined.

objectiveThis study aimed to systematically investigate the characteristics of whole-body and regional body composition changes in patients with primary osteoporosis, and to specifically assess the independent associations of paravertebral muscle fat infiltration and trunk-to-appendicular fat distribution with osteoporosis risk.

methodsBased on diagnostic criteria, participants were categorized into an OP group and a non-OP group. Dual-energy X-ray absorptiometry (DXA) was used to assess bone mineral density (BMD), muscle mass, and fat mass across the whole body and specific regions (trunk, limbs, upper limbs, lower limbs). Computed tomography (CT) was employed to quantitatively evaluate fat infiltration (represented by muscle density) in the psoas major, erector spinae, and multifidus muscles. Spearman correlation analysis was used to assess associations between body composition indicators. Multivariable logistic regression models and restricted cubic spline (RCS) analyses were applied to examine the independent associations of fat infiltration and distribution with OP. Receiver operating characteristic (ROC) curve analysis was performed to evaluate the discriminative ability of the identified adipose measures, with area under the curve (AUC) calculated before and after adjustment for confounders.dipose measures, with area under the curve (AUC) calculated before and after adjustment for confounders.

resultsCompared to the non-OP group, OP patients exhibited significant systemic alterations, including concurrent reductions in whole-body skeletal muscle mass, fat mass, and bone mineral content (all P < 0.01). Regional analysis revealed that bone and fat loss were more pronounced in the trunk than in the limbs (both P < 0.05). CT analysis revealed significantly lower muscle density in the paravertebral muscles of OP patients (all P < 0.05). After adjusting for sex, age, height, weight, total muscle mass, smoking, and alcohol consumption, multivariable logistic regression identified both decreased multifidus muscle density (OR: 0.98 per HU, 95% CI: 0.96-1.00; P = 0.023) and an increased limbs-to-trunk fat ratio (OR: 14.35, 95% CI: 2.90-76.35; P = 0.001) as factors independently associated with OP. Further analysis revealed distinct risk patterns: the limbs-to-trunk fat ratio demonstrated a significant linear dose-response relationship (P for overall association from RCS = 0.015). For multifidus muscle density, while a significant association was observed in the linear model, the more flexible RCS model did not confirm a significant overall association (P for overall = 0.065). ROC analysis showed that after adjustment, the limbs-to-trunk fat ratio had an AUC of 0.777, with a cut-off of 0.785 yielding 51.1% sensitivity and 80.0% specificity; multifidus muscle density had an adjusted AUC of 0.774, with a cut-off of 24.75 HU yielding 80.9% sensitivity and 46.8% specificity.

conclusionThis study characterizes the body composition profile of primary osteoporosis as a composite of changes, including proportional whole-body reduction of muscle and fat, preferential loss of trunk tissues, and significant fat infiltration in paravertebral muscles. Decreased multifidus muscle density and an increased limbs-to-trunk fat ratio are independently associated with OP, showing different association patterns. Both measures demonstrated moderate discriminative ability for osteoporosis after adjustment for confounders, with the limbs-to-trunk fat ratio showing higher specificity and multifidus muscle density showing higher sensitivity. These findings support the concept that OP is a systemic disorder involving bone, muscle, and adipose tissue, providing new perspectives for future risk assessment and intervention strategies.