Corticosteroids are a class of steroid hormones that are produced in the adrenal cortex of vertebrates, as well as the synthetic analogues of these hormones. They have been commonly prescribed for sufferers of knee pain and inflammation, called synovitis, or knee osteroarthritis. In common with most steroids, these drugs are associated with a wide variety of adverse side effects. Depending on the dose, these may include:

Elevated pressure in the eyes (glaucoma)
Fluid retention, causing swelling in your lower legs
High blood pressure
Problems with mood, memory, behavior and other psychological effects
Weight gain, with fat deposits in your abdomen, face and the back of the neck

Taking the drugs over a longer period may produce:

Clouding of the lens in one or both eyes (cataracts)
High blood sugar, which can trigger or worsen diabetes
Increased risk of infections
Thinning bones (osteoporosis) and fractures
Suppressed adrenal gland hormone production
Thin skin, bruising and slower wound healing

A recent study (full text here) has shown that a group of patients injected with a corticosteroid medication over two years showed no decrease in pain, relative to a group taking placebos. However, the ‘placebo group’ did not suffer the loss of cartilage (indicating progression of the condition) over that period.