Intramembranous ossification and endochondral ossification are impaired differently between glucocorticoid-induced osteoporosis and estrogen deficiency-induced osteoporosis

A fracture is the most dangerous complication of osteoporosis in patients because the associated disability and mortality rates are high. Osteoporosis impairs fracture healing and prognosis, but how intramembranous ossification (IO) or endochondral ossification (EO) during fracture healing are affected and whether these two kinds of ossification are different between glucocorticoid-induced osteoporosis (GIOP) and estrogen deficiency-induced osteoporosis (EDOP) are poorly understood. In this study, we established two bone repair models that exhibited repair via IO or EO and compared the pathological progress of each under GIOP and EDOP. In the cortical drill-hole model, which is repaired through IO, osteogenic differentiation was more seriously impaired in EDOP at the early stage than in GIOP. In the periosteum scratch model, in which EO is replicated, chondrocyte hypertrophy progression was delayed in both GIOP and EDOP. The in vitro results were consistent with the in vivo results. Our study is the first to establish bone repair models in which IO and EO occur separately, and the results strongly describe the differences in bone repair between GIOP and EDOP.