Surgical instability from medial meniscal tear, similar to that described for rats, results in cartilage degeneration in knee joints of guinea pigs. Since guinea pigs preferentially load the medial aspect of the knee joint, this procedure must be done on the medial side in order to induce consistent pathological alterations. Similar surgery on the lateral meniscus results in highly variable to no cartilage degenerative changes.
Three-month-old male guinea pigs (with well-formed tibial tide marks) are anesthetized with Isoflurane and the medial aspect of the right knee clipped and scrubbed in preparation for surgery. If surgery is performed on immature animals, lesions will resemble osteochondrosis rather than OA in histological appearance. The medial collateral ligament is transected, the medial meniscus is grasped with a fine toothed hemostat and reflected proximally toward the femoral condyle. The meniscus is then transected with a scalpel or fine scissors. No attempt is made to close the joint capsule and the skin is closed with 3-0 silk sutures. Animals will generally remove the sutures or they can be left in place without problems occurring.
Obviously, since guinea pigs develop spontaneous OA, the contralateral non-operated joint can be utilized in the evaluation of effects of various manipulations in this model. One potential scenario would be to perform surgery on 4- month-old animals (spontaneous OA would be minimal to mild) and treat for 3 months until the animals are 7 months old. Effects of treatment could be evaluated on the operated knee as well as the non-operated knee.
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