Degenerations in Global Morphometry of Cancellous Bone in Rheumatoid Arthritis, Osteoarthritis and Osteoporosis of Femoral Heads are Similar but More Severe than in Ageing Controls.

We have recently revealed significant differences in microarchitectural properties (i.e. global and local morphometries) and mechanical properties between rheumatoid arthritis (RA), osteoarthritis (OA) and osteoporosis (OP) in cancellous bones. This study compared these properties with those of ageing controls by matching bone volume fraction (BV/TV), the most important determinant for bones' mechanical properties, to investigate whether these bones have similar properties and degenerative potentials. RA, OA and OP femoral heads were harvested from patients undergoing total hip replacement surgery. The selected patients were matched by similar cancellous bone BV/TV, with seven patients in each group. Four samples were prepared from each femoral head and scanned with micro-CT to quantify microarchitectural properties and compression tested to determine mechanical properties. In terms of global morphometry, no significant differences were observed between these diseased bones. In terms of local morphometry, the number of plates in the RA group was significantly greater than that of the OP and control groups. Plate volume density in the RA group was significantly greater than in the control group. Interestingly, the ultimate stresses in the three diseased groups were 77% to 195% lower than in the control group (p < 0.001). Degenerations of global morphometry of cancellous bones in these diseased femoral heads are similar but more severe than in ageing controls matched by BV/TV, as evidenced by pronounced reduction in bone strength. This phenomenon suggests that some local morphometric parameters, along with other factors, such as abnormal collagen, mineralisation, erosion and microdamage, may contribute to further compromising mechanical properties.