Intracortical Bone Mechanics Are Related to Pore Morphology and Remodeling in Human Bone

During aging and in osteoporosis, cortical bone becomes more porous, making it more fragile and susceptible to fractures. The aim of this study was to investigate the intracortical compression- induced strain energy distribution, and determine whether intracortical pores associated with high strain energy density (SED) in the surrounding bone matrix have a different morphology and distribution, as well as different remodeling characteristics than matrix with normal SED. Fibular diaphyseal specimens from 20 patients undergoing a jaw reconstruction (age range 41 to 75 years; 14 men and 6 women) were studied. Bone specimens were µCT-scanned, plastic embedded, and sectioned for histology. Three-dimensional microfinite element models of each specimen were tested in compression, and the SED of the bone immediately surrounding the intracortical pores was calculated within a plane of interest corresponding to the histological sections. The SED of a pore, relative to the distribution of the SED of all pores in each specimen, was used to classify pores as either a high or normal SED pore. Pores with high SED were larger, less circular, and were located closer to the endosteal surface of the cortex than normal SED pores (p < 0.001). Histological analysis of the remodeling events generating the pores revealed that the high SED pores compared with normal SED pores had 13.3-fold higher odds of being an erosive (70%) or formative (7%) pore versus a quiescent pore (p < 0.001), 5.9-fold higher odds of resulting from remodeling upon existing pores (type 2 pore) versus remodeling generating new pores (type 1 pore) (p < 0.001), and 3.2-fold higher odds of being a coalescing type 2 pore versus a noncoalescing type 2 pore (p < 0.001). Overall, the study demonstrates a strong relationship between cortical bone mechanics and pore morphology, distribution, and remodeling characteristics in human fibular bone.