The two most commonly used injections into the knee are of steroid and of a shock absorbing substance called hyaluronic acid. Injections into the knee carry a small risk of introducing infection and should therefore be performed in aseptic (very clean) surroundings and with an aseptic technique.
Hyaluronic acid can be used in early arthritis to improve the shock absorbing and health of the cartilage that is still intact. It generally entails a single injection into the knee and the success rate is good but not 100%. The period of relief of symptoms gained is also variable and ranges from days to years.
Steroid is very commonly used as it is a potent anti-inflammatory drug. However it is also toxic to cartilage and as such , in Mr Shepard's opinion, should only be used in inflammatory arthritis or in advanced cases of arthritis when the patient is unfit for joint replacement.