The most effective treatment for reducing lameness and swelling in horses due to acute exacerbations of inflammation with chronic arthritis (also known as osteoarthritis or degenerative joint disease) is intra-articular corticosteroid. It is also one of the most controversial. To understand this controversy you have to consider two aspects of the treatment of arthritis: treatments that modify the clinical signs (pain and lameness) and those that modify the disease process (degeneration of the joint).

It seems logical that any treatment that reduces pain is likely to also slow down the disease process but this is not always true. Back in the 60's it was noted that equine joints that were repeatedly injected developed advanced stages of DJD faster than those not injected. Since that time we have learned that the particular steroid and the way it is used may not only prevent the problem of steroid induced arthopathy but may also slow down the progress of the arthritis. This article discusses the pros and cons of the commonly available glucocorticoids and recommendations for their use.

Corticosteroids are potent anti-inflammatory agents that inhibit the inflammatory process at virtually all levels. Corticosteroids generally have their greatest effect by inhibiting the migration of (white blood cells) leukocytes to sites of inflammation but have effects on the chemical basis of inflammation also. This action is mainly through the inhibition of the breakdown of membrane phospholipids to arachadonic acid which is the first step to the production of a number of inflammatory and reactive molecules, including prostaglandins, peroxides, and leukotrienes.

More recently in mouse joints with inflammation and more reasonable dosage regimens favorable effects of corticosteroids have been described including less chondrocyte cell death and improved healing when compared to controls. Carefully conducted studies in horses with induced arthritis also revealed beneficial long term effects of the two steroids triamcinolone (Vetalog) and betamethasone (Celestone). The improvements included improved quality of synovial fluid, synovial membrane, and articular cartilage morphological parameters along with improved lameness. Methylprednisolone (Depo-Medrol), despite potent anti-inflammatory activity, has not been shown to improve the quality of the joint and at what are thought to be effective clinical sign modifying doses may actually increase the rate of degeneration of the joint.