The development of osteoarthritis in the knee joint is more likely after an injury to the anterior cruciate ligament (ACL). A hallmark of osteoarthritis (OA) is the degradation of cartilage, however, the subchondral bone tissue comprised of a thin subchondrai plate and cancellous bone provides support for the overlying cartilage, yet little is known about the role of bone in the aetiology of OA. Using a canine mode1 for experimental OA, a unilateral transection of the ACL was performed (ACLX), with the contralateral lirnb serving as a control. Adaptation of the periarticular subchondral bone was assessed using quantitative computed tomography, and it was found that bone minera1 density (BMD) was decreased as early as 3 wk post-ACLX, and that there was considerable inhomogeneity of the changes throughout the joint. The microstructural changes reflecting the BMD decreases were evaluated using micro-computed tomography (μCT), and the primary morphological changes included thinning of the trabeculae (-33%) and decreased bone volume ratio (-42%). The decreased anisotropic distribution (-10%) of the microstructure indicated that loading may play a role in the bone adaptation, and the increased 3D connectivity (127%) suggested that the rernodelling may be irreversible. A novel device to measure strain was developed, and it was found that the stiffness of the ACLX bone decreased (-45%). Using these data combined with μCT-based specimen-specific finite element models it was determined that tissue modulus did not change (5100±600 MPa). Thus, large changes to periarticular cancellous bone occur in the early stages of experimental OA, and these changes were dorninated by geometric changes indicating that prevention or slowing of bone adaptation should focus on geometric adaptation of the bone microstructure.