When used systemically either orally or intravenously, steroid use is most relevant to rheumatological disease covered elsewhere on this site. Here we are concerned with the use of intra-articular steroids in osteoarthritis (not inflammatory arthritis).
When steroids are used in the joint (especially the knee) they can be very effective in reducing acute pain. Typically the steroid effect works over about 3 weeks and then the pain returns. Unfortunately, steroids themselves can cause damage to cartilage and therefore make the arthritis worse. Their use in osteoarthritis needs to be carefully considered.
Steroids work by reducing inflammation. It is therefore most relevant to osteoarthritis with an inflammatory component. Therefore one needs an understanding of the pathology of osteoarthritis to make steroid use logical. In osteoarthritis there are changes to the cartilage which are worn away (loss of joint space) and then these die and become osteophytes. The bone is exposed and becomes hardened (subchondral sclerosis) and the joint loses it shock absorbance and become prone to cracks. The underliying bone to this bone loses its integrity and becomes weak (cysts). The anatomy becomes distorted and the ligaments become stretched (varus or valgus). These five changes higlighted in italics are considered the hallmarks of osteoarthritis.
So when one understands the this and the action of steroids it can be difficult to recommend it's use especially when the side effects of making it worse are understood.
In osteoarthritis of the knee there can be bouts of inflammation secondary to cracks and tears in the joint. This can result in synovial inflammation. These episodes occur periodically throughout the process of osteoarthritis. There may be some benefit in this context to steroid injection accepting that cartilage may be damaged further.
Typically therefore, steroids may be used in elderly patients with advanced arthritis who are unfit for surgery and in whom systemic therapy (ie. painkillers) has not provided relief. In the other extreme of a young patient in whom there is mild arthritis and is a candidate for surgery however, the steroids could make the condition worse and by risking infection prevent a joint replacement from being performed.
Steroids should therefore be viewed cautiously as a blunt instrument that can cause more damage than good.