Diminished Cartilage Creep Properties and Increased Trabecular Bone Density following a Single, Sub-Fracture Impact of the Rabbit Femoral Condyle

Traumatic injury to articular cartilage can lead to post-traumatic arthritis We used a custom pendulum device to deliver a single, near-fracture impact to the medial femoral condyles of rabbits Impact was localized to a region similar to 3 mm in diameter, and impact stress averaged similar to 100 MPa Animals were euthanized at 0, 1, and 6 months after impact Cartilage mechanical properties from impacted and sham knees were evaluated by creep-indentation testing, and periarticular trabecular bone was evaluated by microCT and histomorphometry Impact caused immediate and statistically significant loss of cartilage thickness (-40% vs sham) and led to a greater than twofold increase in creep strain From 0 to 6 months after impact, the ability of cartilage to recover from creep deformation became significantly impaired (percent recovery different from control at 1 and 6 months) At 1 month, there was a 33% increase in the trabecular bone volume fraction of the epiphysis beneath the site of impact compared to control, and increased bone formation was observed histologically Taken together, these findings demonstrate that a single, high-energy impact below the fracture threshold leads to acute deleterious changes in the viscoelastic properties of articular cartilage that worsen with time, while at the same time stimulating increased bone formation beneath the impact site (C) 2010 Orthopaedic Research Society Published by Wiley Periodicals, Inc J Orthop Res 28 1307-1314, 2010