Fundamental subchondral bone changes in spontaneous knee osteoarthritis.

Osteoarthritis has an unknown aetiology, and tissue samples from early stage human osteoarthritis tissue cannot be reliably obtained. Therefore understanding the development of OA relies on using animal models: such as the spontaneous changes seen in the Dunkin-Hartley guinea pig strain, which are biochemically, histologically and radiologically similar to human OA. We investigated the role of bone change in early OA development using the non-OA developing Bristol strain-2 as control from 3 to 36 weeks by standard microfocal X-ray imaging and histological techniques. The patella, tibia and femur epiphyseal region and immediate subchondral area were analysed for bone density at all ages. We found that both radiological and histological osteoarthritis scores increased progressively for the Dunkin-Hartley, but not for the BS2 demonstrating its value as a control. The Dunkin-Hartley had a higher bone density and greater subchondral bone thickness from 24 weeks of age. We conclude that prior to any gross osteoarthritis pathology the Dunkin-Hartley are undergoing subchondral bone remodelling, thus demonstrating the fundamental role of early bone remodelling in the development of osteoarthritis.