Detecting structural changes in early experimental osteoarthritis of tibial cartilage by microscopic magnetic resonance imaging and polarised light microscopy.

OBJECTIVES: To detect changes in the collagen fibril network in articular cartilage in a canine experimental model of early osteoarthritis (OA) using microscopic magnetic resonance imaging (microMRI) and polarised light microscopy (PLM). METHODS: Eighteen specimens from three pairs of the medial tibia of an anterior cruciate ligament transection canine model were subjected to microMRI and PLM study 12 weeks after surgery. For each specimen, the following experiments were carried out: (a) two dimensional microMRI images of T(2) relaxation at four orientations; (b) the tangent Young's modulus; and (c) two dimensional PLM images of optical retardance and fibril angle. Disease induced changes in tissue were examined across the depth of the cartilage at a microMRI resolution of 13.7-23.1 microm. RESULTS: Several distinct changes from T(2) weighted images of cartilage in OA tibia were seen. For the specimens that were covered at least in part by the meniscus, the significant changes in microMRI included a clear shift in the depth of maximum T(2) (21-36%), a decrease in the superficial zone thickness (37-38%), and an increase in cartilage total thickness (15-27%). These microMRI changes varied topographically in the tibia surface because they were not significant in completely exposed locations in medial tibia. The microMRI results were confirmed by the PLM measurements and correlated well with the mechanical measurements. CONCLUSION: Both microMRI and PLM can detect quantitatively changes in collagen fibre architecture in early OA and resolve topographical variations in cartilage microstructure of canine tibia.