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

An increased risk of fracture is a feature of rheumatoid arthritis and of a nimal models of inflammatory arthritis. We examined geometrical changes in the metaphyseal cortex of the distal femur in an animal model of inflammato ry arthritis. Additionally, we examined the effect of a bisphosphonate in p reventing these changes. Five groups of rabbits were studied: normal contro ls, those with inflammatory arthritis, and three groups with arthritis trea ted with bisphosphonate. To determine geometrical properties, image analysi s was performed on digitized cross sections of the femoral metaphyseal cort ices. The results demonstrated that the posterior cortical wall was signifi cantly less thick in rabbits with arthritis than in normal rabbits and in t he rabbits in the three bisphosphonate treatment groups (p < 0.05). Moment of inertia about the lateral-medial axis was reduced in rabbits with arthri tis compared with normal rabbits (p < 0.05). Cross-sectional area was not s ignificantly different between groups. The changes suggest a mechanism of w eakening of bone in arthritis; when the results are coupled with results of previous porosity studies, severe directional weakness is apparent. Bispho sphonate was effective in preserving bone integrity in inflammatory arthrit is.