Temporary side effects of cortisone knee injections include localized pain, elevated blood sugar, facial redness and whitening of skin around the injection site, explains About.com. Serious complications include infection, nerve damage and damage to nearby bones, says Mayo Clinic.
Mayo Clinic explains that overuse of cortisone shots may carry a greater risk of complications, such as cartilage damage, weakened tendons and bone death or damage. Cortisone shots should not be given more than four times a year.
WebMD explains that cortisone shots only provide temporary relief, and they become less effective with each subsequent use. The shots should be used for pain management during pain flare-ups, not as a regular treatment.