When used properly, the effect of a knee injection of cortisone for osteoarthritis can last for months to years, according to MedicineNet. Corticosteroids reduce inflammation, which produces pain relief. When inflamed tissue in a small area is causing the pain, the injection can treat the problem permanently.
Injecting a corticosteroid directly in the knee to treat the inflammation locally is a more powerful and effective treatment than administering aspirin or other anti-inflammatory medications orally, notes MedicineNet. The injection bypasses stomach irritation and other side effects associated with oral medications. Cortisone injections are outpatient procedures easily performed in the doctor's office.
Synvisc, or hylan G-F 20, is a prescription drug injected into the knee to treat osteoarthritis, explains RxList. Synvisc is a viscosupplement or hyaluronan injection that a doctor administers in the office once a week for three weeks. The injections provide osteoarthritis knee pain relief for up to six months.