Therapeutic Injections for Osteoarthritis of the Knee

If physical therapy and pain medication taken by mouth don’t relieve the aching pain caused by osteoarthritis of the knee, doctors may recommend an injection of medicine directly into the arthritic joint. Therapeutic injections may give you the relief you need to begin physical therapy or other exercise to strengthen the muscles supporting the knee.

An injection of corticosteroids or hyaluronic acid may reduce inflammation and ease pain. Other more experimental injections—such as platelet-rich plasma or stem cells—may relieve pain and encourage healing in damaged soft tissues. Your doctor can discuss whether you are a candidate for these experimental injections, which are not approved by the U.S. Food and Drug Administration (FDA) to treat knee osteoarthritis. Some people find that therapeutic injections provide long-term pain relief and help them remain active, but they may not be appropriate for everyone.

Our doctors can use live X-ray or ultrasound imaging to guide the injection precisely into the knee joint, ensuring that the medication has the maximum effect.

Corticosteroid Injection

Corticosteroids are powerful anti-inflammatory medications that are very effective in alleviating pain caused by joint inflammation. For some people, this medication can provide long-lasting relief when injected directly into a joint.

Typically, doctors inject a small amount of anesthetic in addition to corticosteroids. The anesthetic can provide short-lasting but immediate pain relief in the knee, which in itself is an important piece of diagnostic information—if the anesthetic relieves pain, doctors can rule out other sources of discomfort, such as a muscle strain. This anesthetic wears off a few hours after the injection, at which time knee pain may return. This is normal. The corticosteroid begins to work two to three days later.

In some people, a corticosteroid injection provides pain relief that lasts for many months, and in others, the injection doesn’t work at all. Most people experience some pain relief, lasting for a few weeks or months.

Doctors recommend no more than two or three corticosteroid injections in the knee per year. If used too frequently, corticosteroids may cause side effects including weakening of soft tissues in the knee and skin discoloration at the injection site. In addition, corticosteroid use can increase blood sugar levels and may not be appropriate for people with certain metabolic conditions, such as diabetes.

Hyaluronic Acid Injection

The healthy knee joint contains a small amount of a gel-like substance called synovial fluid. Synovial fluid contains a unique component called hyaluronic acid, which cushions and lubricates the joint during activity. As people age, the hyaluronic acid can break down, causing the synovial fluid to become thinner and less effective as a lubricator and shock absorber.

To address the changes in the synovial fluid of knees affected by osteoarthritis, doctors at NYU Langone inject into the knee joint a hyaluronic acid product that has been approved by the U.S. Food and Drug Administration (FDA). The injection is designed to make the fluid more substantial and to improve the joint’s gliding motion. This improved joint function may provide pain relief that lasts months or longer.

These injections do not provide relief to everyone, as is the case for all osteoarthritis treatments. Researchers at NYU Langone continue to investigate how to identify whether a person is likely to benefit.

Your doctor may recommend a single injection or a series of three injections administered once per week. NYU Langone doctors generally prescribe hyaluronic injections a maximum of twice per year.

What to Expect After Corticosteroid or Hyaluronic Acid Injections

Most people can return home or to work immediately after the injection takes place. The site of the injection may be swollen or tender for one or two days. Doctors may recommend applying ice two or three times a day or taking an over-the-counter medication to relieve pain and reduce swelling.

It may take several weeks to see improvement after a hyaluronic acid injection. Our doctors recommend restricting high-impact activity, such as running, until symptoms improve.

A person may feel the pain relief effects of corticosteroid injections more quickly than hyaluronic acid, but the results may not last as long. However, each person may respond differently to either of these injections.

Platelet-Rich Plasma Injection

An injection of platelet-rich plasma is an experimental technique that your NYU Langone doctor may discuss using as part of a comprehensive treatment plan. The injection consists of a natural substance, called platelet-rich plasma (PRP), into the knee that may help injured tissue heal more quickly. Platelet-rich plasma is composed of blood cells called platelets that are taken from your own blood. Platelets help tissues heal after an injury by releasing substances called growth factors that stimulate healing.

In this procedure, a doctor takes a small amount of your blood from a vein in your arm and uses a machine called a centrifuge to separate the platelets and growth factors from other blood components. This process takes about 15 minutes. A doctor then injects this platelet-rich liquid, called plasma, directly into the knee joint. Our doctors use ultrasound guidance to ensure precision.

People often experience pain relief and improved function within two to six weeks.

Stem Cell Injection

Doctors at NYU Langone offer an experimental technique involving injections of stem cells. Stem cells are unique in that they can develop into any type of cell—for example, cells that help repair damaged tissue. When injected into an arthritic knee, stem cells may encourage the damaged cartilage to regrow and heal. Injections of stem cells can also reduce inflammation.

The exact way stems cells work is still being researched, but some people find that an injection of stem cells relieves pain and swelling and may help speed recovery.

Our doctors obtain these stem cells from your body, typically from bone marrow in your pelvic bone, using a syringe. The area is thoroughly numbed before the stem cells are extracted, but the procedure may cause mild discomfort. After the stem cells are separated from blood and other substances in the bone marrow, they are injected directly into the knee.

Stem cell therapy does not produce results right away. Over time, their regenerative effect may help damaged tissues to heal. Most people experience improved function and relief from pain after two to six weeks.

What to Expect After PRP or Stem Cell Injections

Doctors recommend avoiding anti-inflammatory drugs such as ibuprofen for four to six weeks after a therapeutic injection with stem cells or platelet-rich plasma while the injury heals. This is because injections of biologic material stimulate the body’s inflammatory response, an important part of healing. If the injection site is sore or swollen in the days after treatment, doctors recommend taking over-the-counter acetaminophen and applying an ice pack for 15 minutes at a time three times a day.

You should also avoid strenuous activities using the knee for four weeks after an injection to give the injured tissue time to heal. Your doctor may provide you with a boot to keep your foot and leg immobile. All weight should be kept off of the knee for two days, and your doctor can provide you with crutches to help you move around without putting weight on the joint. The boot should be worn for two to three weeks.

Your doctor schedules a follow-up appointment after three or four weeks to evaluate the healing process. He or she may recommend an additional platelet-rich plasma or stem cell injection depending on the extent of the injury.

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