Reorganization of the femoral cortex due to age-, sex-, and endoprosthetic-related effects emphasized by osteonal dimensions and remodeling.

Cortical remodeling is of particular importance to femoral strength. However, osteonal morphology and its quantitative changes are still poorly understood. Therefore, osteons as the cortexes basic structural units should serve for histomorphometrical assessment of reorganization mechanisms. Total hip replacement (THR) cases as well as relevant controls were investigated to gain insight into changes within stress shielded as well as age- and sex-associated bone with emphasis on the underlying osseous cell interactions. Control (n = 23) and THR (lifetime Ø14 months, n = 8) femora were prepared to grinding specimen. Osteon density (On.Dn.), osteon area (On.Ar.), haversian canal area (H.Ar.), osteon mean wall thickness (MWT), and cortical porosity (Ct.Po.) were evaluated periosteal and endosteal. Osteonal activity (OA) was determined by mineralization differentiation of active and quiescent osteons. Sex- and age-related differences in osteonal remodeling were evident in controls. Females showed age-dependent increases of H.Ar. during concomitant changes of On.Ar. and MWT resulting in elevated Ct.Po. at the entire cortex. Males showed this occurrence only periosteal. Increased OA and therefore higher remodeling rates were found in females above 70 years. THR led to decreased On.Dn. at the entire cortex. Periosteal increased OA represented increased periprosthetic remodeling resulting in elevated H.Ar., which enhanced Ct.Po.. Massive losses of endosteal circular osteonal structures following THR are reflected in a spongy reorganized cortex leading to increased Ct.Po.. Imbalances in osteoblast-osteoclast interactions whose intensity is related to the respective cortex regions occur in both stress shielded and aging bone and may thus contribute to implant failure and fracture risk. (c) 2009 Wiley Periodicals, Inc.