The generation of enlarged eroded pores upon existing intracortical canals is a major contributor to endocortical trabecularization

The gradual conversion of cortical bone into trabecular bone on the endocortical surface contributes substantially to thinning of the cortical bone. The purpose of the present study was to characterize the intracortical canals (3D) and pores (2D) in human fibular bone, to identify the intracortical remodeling events leading to this endocortical trabecularization. The analysis was conducted in fibular diaphyseal bone specimens obtained from 20 patients (6 women and 14 men, age range 41-75 years). mu CT revealed that endosteal bone had a higher cortical porosity (p < 0.05) and canals with a larger diameter (p < 0.05) than periosteal bone, while the canal spacing and number were similar in the endosteal and periosteal half. Histological analysis showed that the endosteal half versus the periosteal half: (i) had a higher likelihood of being non-quiescent type 2 pores (i.e. remodeling of existing pores) than other pore types (OR = 1.6, p < 0.01); (ii) that the non-quiescent type 2 pores contributed to a higher porosity (p < 0.001); and that (iii) amongst these pores especially eroded type 2 pores contributed to the elevated cortical porosity (p < 0.001). In conclusion, we propose that endocortical trabecularization results from the accumulation of eroded cavities upon existing intracortical canals, favored by delayed initiation of bone formation.