Due to the dynamic nature of the skeletal system and its structural adaptation to local mechanical loading environments, substantial variation exists in the size, shape, and material components of each bone. The human rib uniquely differs from other skeletal elements in the body as it undergoes consistent and cyclic loading during ventilation. Standard clinical bone quality assessment using dual-energy x-ray absorptiometry (DXA) is often based on measurements of areal bone mineral density (aBMD) from the femoral neck and/or lumbar spine1 which does not account for heterogeneity in fracture risk due to localized adaptations across the body. Additionally, evidence has shown that fracture risk increases independently of DXA aBMD t-scores2, 3, 4. Further, these discrepancies are exacerbated in the elderly where age-related skeletal changes (e.g. osteoarthritis) can skew measures of aBMD5,6. Rib fractures result in increased patient morbidity and mortality7 and decreased health-related quality of life. Unsurprisingly, recent work has demonstrated the inability of lumbar aBMD to predict experimental rib strength8 suggesting that standard clinical DXA assessments do not accurately represent rib fracture risk. The current lack of accurate screening techniques in the thorax may obscure treatment or rib fracture prevention efforts, especially in older adults who experience higher complication rates9,10 and increased morbidity and mortality following rib fractures11.

More recently, quantitative computed tomography (QCT) has become an important clinical tool12 in understanding factors, particularly volumetric bone mineral density (vBMD), that influence bone quality and strength and may identify those at risk for fracture with increased sensitivity over DXA13. Previous work has demonstrated that not only does vBMD vary between sexes14, but trabecular vBMD varies between skeletal elements15, indicative of the effects of variable loading environments and bone remodeling on mineralization. Using QCT, previous research has reported that vBMD vary's even within a single appendicular skeletal element16,17, suggesting that variation in BMD may aid assessments of fracture risk18 and are likely more representative than global assumptions of bone quality. While evidence of vBMD variation has been demonstrated in the extremities16,17 and weight-bearing bones17,19, these trends, as well as the influence of age and sex, have yet to be investigated in the rib which has adapted to a unique mechanical loading environment.

Due to the potential severity and long-term effects of rib fractures, accurately assessing rib bone quality may help inform injury mitigation efforts and improve health outcomes for patients. However, current clinical guidelines are likely insufficient to accurately quantify components that influence fracture risk in the rib. Therefore, the purpose of this study is to quantify variation in vBMD along the length of the rib, determine the influence of sex and age, and investigate if standard clinical methods for assessing bone quality, DXA, has a relationship with vBMD in the rib.