Changes in cross‐sectional geometry of the distal femoral metaphysis associated with inflammatory arthritis are reduced by a bisphosphonate (zoledronate)

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Abstract
An increased risk of fracture is a feature of rheumatoid arthritis and of animal models of inflammatory arthritis. We examined geometrical changes in the metaphyseal cortex of the distal femur in an animal model of inflammatory arthritis. Additionally, we examined the effect of a bisphosphonate in preventing these changes. Five groups of rabbits were studies: normal controls, those with inflammatory arthritis, and three groups with arthritis treated with bisphosphonate. To determine geometrical properties, image analysis was performed on digitized cross sections of the femoral metaphyseal cortices. The results demonstrated that the posterior cortical wall was significantly less thick in rabbits with arthrits than in normal rabbits and in the rabbits in the three bisphosphonate treatment groups (p < 0.05). Moment of inertia about the lateral-medial axis was reduced inrabbits with arthritis compared with normal rabbits (p < 0.05). Cross-sectional area was not significantly different between groups. The changes suggest a mechanism of weakening of bone in arthritis; when the results are coupled with results of previous porosity studies, severe directional weakness is apparent. Bisphosphonate was effective in preserving bone integrity in inflammatory arthritis.