The point of knee shots

An estimated 19% of men ages 60 and older suffer from knee osteoarthritis. Symptoms include pain while moving, stiffness, swelling, tenderness, and limited range of motion.

Men can often manage the pain and improve mobility with lifestyle changes, such as weight loss, physical therapy, and exercises focusing on joint movement and strengthening leg muscles. Taking occasional over-the-counter or prescription pain relievers or anti-inflammatory medicines also can help. These can be taken in pill form or topically (applied to the skin).

But if these strategies don't offer sufficient relief, or if symptoms impede your ability to move freely, you may benefit from a medication injection.

"Injections can provide immediate pain relief, reduce inflammation, and increase mobility," says rheumatologist Dr. Robert Shmerling, the former clinical chief of the division of rheumatology at Harvard-affiliated Beth Israel Deaconess Medical Center.

"But not everyone improves, and even if they are helpful, injections are a temporary treatment that won't cure your knee osteoarthritis or change the course of the disease. If you must rely on repeated injections for pain management and help with mobility, then it's probably time to consider a knee replacement."

There are two main types of injections for knee osteoarthritis: corticosteroids and hyaluronic acid.

Corticosteroid injections

Corticosteroid injections (also known as steroid shots) are often doctors' first choice. Corticosteroids are manufactured drugs that resemble cortisol, a hormone the adrenal glands produce. They reduce inflammation, pain, and swelling in and around the knee joint. Your doctor will first treat the knee with a local anesthetic. If the knee has extra swelling, your doctor may remove excess fluid with a needle.

Joints are surrounded by synovial fluid, which helps cushion and lubricate the moving parts of the knee. However, when cartilage is damaged from osteoarthritis, the body responds by overproducing synovial fluid, which leads to swelling. "Removing fluid relieves pressure and swelling around the knee joint and makes the steroid injection more effective," says Dr. Shmerling.

Once any excess fluid is removed, the corticosteroid (usually mixed with a numbing agent) is injected into the knee joint. Your doctor may use ultrasound to help guide the needle. The procedure is rarely painful, though you may feel some discomfort.

"Relief from the numbing agent kicks in right away, while the corticosteroid takes about 24 hours to start working on your symptoms," says Dr. Shmerling. "If you don't feel the effects within 72 hours, the injection probably won't work for you."

Common side effects are pain and swelling around the injection site, which usually goes away within 48 hours. Your knee also may feel tender, so you should avoid strenuous activities for a few days. "You may want to take an over-the-counter pain medication to reduce any discomfort," says Dr. Shmerling. "Otherwise, regular rest is all you need."

The injection's effect can last from several weeks to months. Repeat injections can be given every three to four months. "But keep in mind that a shot often works best the first time," says Dr. Shmerling. "Over time, they may work less well and for shorter periods. If the pain and inflammation improve for only a week or two after the first injection, you probably won't benefit much from future ones." Studies also have suggested that relying too much on injections may damage cells in the knee that make cartilage, which can worsen the joint deterioration.

Hyaluronic acid injections

Another injection therapy involves using a synthetic version of hyaluronic acid. "This is usually recommended only if a corticosteroid injection doesn't work or if you have diabetes and your doctor is concerned about possible side effects from the steroid, such as higher blood sugar levels," says Dr. Shmerling.

Hyaluronic acid is a natural component of the synovial fluid in the joints. However, as osteoarthritis advances, hyaluronic acid decreases, which makes synovial fluid thinner and less effective. "This can increase pain and stiffness, as there's less lubrication to help the knee joint move freely," says Dr. Shmerling. "The synthetic hyaluronic acid acts like oil on a rusty joint."

Possible side effects include pain at the injection site, inflammation in the knee soon after injection (as a reaction to the medication), and infection. "If the injection provided significant benefit, a follow-up injection may be given after six months," says Dr. Shmerling.

If you take any type of anticoagulant (blood thinner), be sure to let the doctor know before getting any injections, because it increases your risk of bleeding into and around the joint.

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