Following the injection of cortisone or hyaluronic acid into the knee, there may occasionally be increased pain or an inflammatory reaction to the injected medication. These reactions usually occur within the first 24 to 48 hours after the injection and ice, elevation, and medications such as analgesic can help. Injections into a joint must always be done under sterile conditions to minimize the possibility of infection. If an infection does occur after the knee has been injected, it must be dealt with promptly to avoid irreversible destruction of the joint cartilage. Pain greater than expected, swelling and/or redness of the knee joint or the development of a fever should raise concerns about an infection.