Sander M. Botter, Gerjo J.V.M van Osch, Stefan Clockaerts, Jan H. Waarsing, Harrie Weinans, Johannes P.T.M. van Leeuwen
In osteoarthritis (OA) changes occur both in cartilage and subchondral bone. The subchondral bone plate facilitates normal crosstalk between articular cartilage and trabecular subchondral bone, and adaptive changes in the plate due to OA may therefore disturb crosstalk homeostasis. To investigate these changes over time we examined the cartilage-subchondral bone interface using a combined approach of histology and in vivo micro CT. Male C57Bl/6 mice (n=8), aged 16 weeks, received intra-articular injections with collagenase in one joint to induce instability-related OA and saline into the contralateral knee joint (controls). At 2, 4, 6, 10 and 14 weeks post-injection, changes in the tibial subchondral bone plate and subchondral trabeculae were analyzed. At two weeks post-injection, collagenase injected joints had significantly more cartilage damage and osteophytosis than control joints. Osteoclast activity directly underneath the subchondral bone plate was significantly elevated (Oc.S./BS controls: 7.60± 0.81%; OA: 11.07± 0.79%), causing the plate to become thinner and creating a large increase in subchondral bone plate porosity (cumulative porosity volume controls: 0.05e-3 ± 0.04e-3 mm3; OA: 2.52e-3 ± 0.69e-3 mm3). At four weeks post-injection, the previously formed perforations disappeared, coinciding with a significant rise in osteoblast activity in the subchondral trabecular bone (bone formation rate controls: 0.30± 0.03, OA: 0.62± 0.13 μm2/μm3*day). The current study provides for the first time quantitative longitudinal data on the dynamic changes in the subchondral bone plate after OA induction. The development of plate perforations may enhance mutual interaction between subchondral trabeculae, bone marrow cells and the articular cartilage in OA.