Journal of Osteoporosis and Physical Activity
Open Access

Abstract

Quantity Does Not Reflect Quality- Musculoskeletal Health in Obese Peri- Pubertal Girls

Krista Casazza

Recent studies have challenged the traditionally accepted view that obesity is beneficial to the growing skeleton. Despite having greater bone mineral content (BMC) and lean mass when assessed by dual X-ray energy absorptiometry (DXA), compromise in skeletal integrity (i.e. fracture, joint pain) are increasingly being reported in the pediatric population. The objective of this study was to evaluate the relationship between absolute quantitative (mass) and qualitative aspects of bone and muscle (cortical and trabecular density, muscle and marrow density, and stress strain index; SSI) in obese peri-pubertal girls ages 7-11 years. Mass (bone, fat and lean) was assessed by DXA and density, strength and fatty infiltration was evaluated by peripheral quantitative computed tomography (pQCT). pQCT scans were performed at 4% and 66% of radius length as well as 66% of the tibia length. All girls were obese BMI % (>95th). Statistical analysis was conducted using the sample mean body fat percentage girls to stratify into two groups, obese (<43.78%), and morbidly obese (>43.78 %). BMC and lean mass were not significantly different between the groups. Total body fat was positively associated with both lean and bone mass in both groups. Total body fat was inversely associated with cortical density and SSI in the upper and lower extremity. SSI at 4% in the radius was significantly lower in the morbidly obese group, yet the trabecular and cortical density of the upper extremity was higher. In addition, marrow area was greater yet marrow density, an estimate of bone marrow adipose tissue was significantly lower in the morbidly obese group (p<0.05). This study extends these observations to demonstrate the impact of obesity in the context of bone and muscle quality and suggest the increased fracture in obese, particularly morbidly obese girls, rates may be due to the adverse impact of obesity on musculoskeletal health.