High-resolution NMR imaging of an antigen-induced arthritis in the rabbit knee.

High-resolution, serial, spin-echo images were obtained for an antigen-induced knee arthritis in six rabbits. The animals were imaged prior to intra-articular challenge and at various time points up to 14 weeks after challenge. Extensive high-signal inflammatory changes were seen at Day 1 in the lymph node, capsule, and surrounding muscle. The muscle and lymph node response decreased rapidly after the first week. The capsule high-signal area reached a maximum at Day 10, but was still extensive at Day 39. The infrapatellar fat pad was replaced more slowly by high signal and the appearance of high signal in both the tibia and femur was a late change. Terminal histological examination showed that the capsule and fat pad high-signal areas corresponded to fibrous and synovial proliferation. The bone changes were a result of edema and cyst formation. The separation of the various time courses of the inflammatory changes may be of value in understanding the model and evaluating potential anti-arthritic drugs.