Degenerative Joint Disease Induced by Repeated Intra-Articular Injections of Monosodium Urate Crystals in Rats as Investigated by Translational Imaging

Abstract

\n Effects of repeated injection of monosodium urate (MSU) crystals, in combination with lipopolysaccharide (LPS), into rat knee joints every two weeks for a maximum of five administrations were investigated. Joint swelling, nociception and hard/soft tissue changes were assessed longitudinally by non-invasive imaging. MSU crystals induced joint swelling, synovial membrane thickening, fibrosis of the infrapatellar fat pad, tidemark breaching, and cartilage invasion by inflammatory cells. Several inflammatory proteins were present in synovial fluid. A higher sensitivity to mechanical stimulus was detected in paws of limbs receiving MSU/LPS compared to saline-injected limbs. In MSU/LPS-challenged joints, magnetic resonance imaging (MRI) revealed increased synovial fluid volume in the posterior region of the joint, alterations in the infrapatellar fat pad reflecting a progressive decrease of fat volume and fibrosis formation, and a significant increase in the relaxation time T2 in femoral cartilage, consistent with a reduction of proteoglycan content. MRI also showed cyst formation in the tibia, femur remodeling, and T2 reductions in extensor muscles consistent with fibrosis development. Repeated intra-articular MSU/LPS injections in the rat knee joint induced pathology in multiple tissues and may be a useful means to investigate the relationship between urate crystal deposition and the development of degenerative joint disease.