There are two possible choices: steroid injection or hyaluronic acid. You will have to check with your doctor to find out which one is planned.
The steroid injection is a combination of three drugs. There's a local anesthetic like Xylocaine or lidocaine. This agent gives fast pain relief. There are two steroid compounds given for their antiinflammatory properties. One is a slow-acting drug. The other is more quick-acting. Studies report combining the steroid with the anesthetic gives pain relief for up to three weeks.
The other type of injectable treatment is with a joint fluid replacement. Most often hyaluronic acid is used. This is actually made from the coxcombs of roosters. It's injected into the joint in a series of about three injections over six months time. It acts to lubricate the knee in patients who still have some cartilage left. There's a 50-50 chance it will work to give you less pain and more protection to the joint.