Effects of intra-articular administration of methylprednisolone acetate on normal articular cartilage and on healing of experimentally induced osteochondral defects in horses.

This study, conducted on eight horses, evaluated the impacts of regularly injecting the steroid methylprednisolone acetate (MPA) into a horse’s joint, either where there was a significant cartilage defect or where the cartilage was healthy. The researchers found that MPA seemed to inhibit healing in joints where cartilage damage had been artificially induced while also causing structural and cellular changes in the healthy cartilage.

Study Design and Methodology

• The study involved two groups of horses. The first group had a created full-thickness defect, a severe type of joint damage, in the cartilage of their radial carpal bone — a joint in a horse’s leg. The second group had no inflicted cartilage damage.
• In both groups, one joint was selected at random to be treated with 100 mg injections of MPA once a week for four weeks. The other joint functioned as a control and was injected with a sodium chloride solution instead.
• Methylprednisolone acetate is a type of corticosteroid, a class of drugs used to reduce inflammation, a common issue that arises with joint damage.

Study Findings

• After 16 weeks, the horses were euthanized and the joints were evaluated. The researchers found notable differences between the joints treated with MPA and the control joints.
• In the horses with the artificially induced defect, less than half of the control joints had developed a repair tissue (called fibrocartilage), whereas none of the joints treated with MPA showed any such development.
• Moreover, the tissue that did develop in the MPA-treated joint was a thin fibrous tissue, unlike the firmly attached fibrocartilage seen in the control joint.
• Further, changes were observed in the joints with originally healthy cartilage that had been treated with MPA. These changes included the formation of chondrocyte clusters, loss of the palisading architecture (the organized arrangement of cells), and cell death. These changes are generally negative, often resulting in a reduction of the healthy function of the cartilage.

Concluding Summary

• The regular administration of methylprednisolone acetate into a horse’s joint appears to inhibit the development of repair tissue following severe cartilage damage. It also initiates negative morphological and cellular changes in healthy cartilage.
• Considering these observations, the usage of MPA in horses might require careful evaluation, considering its potential adverse effects on the healing process, and overall health of normal cartilage.