Injections to Relieve Knee Pain

Knee osteoarthritis is the most common form of osteoarthritis in the United States. It is caused by progressive degeneration of the cartilage in the knee joint, which protects bones in this area from rubbing against each other. While there is no cure for osteoarthritis, also referred to as wear-and-tear arthritis or degenerative joint disease, treatments can help reduce pain and inflammation.

If oral medications do not help with your knee osteoarthritis pain, your doctor may suggest injecting a medication directly into the knee joint. Knee injections used for arthritic pain include corticosteroid (cortisone), hyaluronic acid (gel), platelet-rich plasma, placental tissue matrix, Botox, and reverse injection (fluid aspiration). 

Corticosteroids, or cortisone, are anti-inflammatory medications that can reduce pain, swelling, and inflammation. They are the most commonly used knee injections for treating knee pain from osteoarthritis. According to the American College of Rheumatology and Arthritis Foundation guidelines for managing knee osteoarthritis, corticosteroid injections are recommended over other types of injections due to improved outcomes and effectiveness in alleviating symptoms.

Corticosteroid injections are performed under local anesthesia: You will be awake for the procedure, but your knee will be numbed. A small amount of anesthesia will be injected into your knee before the corticosteroid. The anesthesia can provide immediate, short-term pain relief in the knee, but begins to wear off a few hours after the injection. You may experience pain at this time until the corticosteroid injection begins to work two to three days later.

These injections can help relieve pain and reduce symptoms between six weeks and six months after the procedure although the injections are not effective for everyone. You will typically not be allowed to receive more than two or three injections per year.

The evidence for cortisone shots in treating knee osteoarthritis is mixed. Patients treated with corticosteroid injections were found to experience greater pain relief and reduced stiffness compared with those injected with saline throughout a two-year study. Cortisone injections, however, have also been linked to cartilage loss and no significant differences in knee pain over time.

Viscosupplementation, sometimes called gel injections, refers to injecting hyaluronic acid into the knee to decrease pain and improve joint movement. Brand names for hyaluronic acid injections include Synvisc-One, Orthovisc, Euflexxa, and Supartz. Hyaluronic acid used for injections is derived from the combs of chickens.

Hyaluronic acid is a gel-like substance that occurs naturally in the synovial fluid within each joint capsule that surrounds all joints. It serves as a lubricant that allows bones to move smoothly within a joint, and provides shock absorption to decrease pressure and friction within joints. Over time, hyaluronic acid levels in joints decrease, especially as the joints wear away in osteoarthritis.

You may receive between one and five injections. If there is excess swelling and fluid buildup in the knee joint, your doctor will use a needle to aspirate, or remove, the fluid before injecting the hyaluronic acid. You should avoid prolonged standing, walking, jogging, running, or heavy lifting for the first 48 hours after receiving a hyaluronic acid injection.

It may take up to four weeks to notice any significant improvement, and the lasting effects can vary from two to six months. Hyaluronic acid injections may be repeated about once every six months.

Similar to corticosteroids, research examining the efficacy of hyaluronic injections has yielded mixed results, with some studies reporting significant pain relief and others reporting no or insignificant effects on pain. No major adverse events were associated with these injections, however.

Prolotherapy, an abbreviation for proliferation therapy,  is an alternative medical treatment that utilizes injections of naturally occurring substances to help the body repair damaged structures. The two main types of prolotherapy injections for managing osteoarthritic knee pain are platelet-rich plasma and placental tissue matrix injections.

Platelet-Rich Plasma (PRP) Injections

Platelet-rich plasma injections are made up of your own blood plasma that contains a high concentration of platelets, also called thrombocytes, which are small blood cells that are involved in blood clotting. Platelets release substances called growth factors that stimulate healing after an injury. When injected into the knee, platelet-rich plasma has the potential to help damaged cartilage heal.

Your doctor will use a syringe to draw a small amount of blood from a vein in your arm and use a centrifuge to separate the plasma and platelets from the white and red blood cells. Blood centrifugation takes about 15 minutes to separate the blood components. Your doctor will then inject the platelet-containing plasma directly into your knee joint. Ultrasound may be used to help guide accuracy of the injection.

A recent study comparing cortisone, hyaluronic, and PRP injections found that PRP injections are superior to the other two in terms of long-term pain relief, specifically at six, nine, and 12 month intervals after treatment.

Placental Tissue Matrix (PTM) Injections

Placental tissue matrices are derived from the placenta, an organ that develops during pregnancy to provide oxygen and nutrients to a developing fetus. The placenta is connected to a growing baby via the umbilical cord, and is expelled from the body during childbirth when the baby is delivered.

The placental tissue is obtained from a healthy mother who had a normal labor and delivery without complications. Once harvested, the placental tissue is cleansed and preserved. The placental cells contain a large amount of growth factors that promote healing. Similar to PRP injections, injections of placental tissue matrix have been shown to help heal damaged cartilage cells and delay changes to the cartilage in osteoarthritis.

You may experience decreased pain and improved use of your knee within two to six weeks after receiving prolotherapy injections with lasting effects up to one year, although neither injections of PRP or PTM are recommended for the treatment of knee osteoarthritis by the American College of Rheumatology and Arthritis Foundation guidelines because there is limited evidence demonstrating overall effectiveness and a lack of standardization of treatment protocols.

Botulinum toxin, commonly known as Botox, is a naturally occurring toxin produced by bacteria that is commonly used to relax forehead wrinkles and decrease muscle spasticity in neurologic conditions by paralyzing nerves.

Preliminary research suggests that Botox injections can be used to treat knee osteoarthritis by paralyzing the nerves that send chronic pain signals to the brain. It may take up to four weeks for the full effect to set in, and pain relief may last up to six months.

Botox injections are also not recommended by the American College of Rheumatology and Arthritis Foundation guidelines due to the small number of clinical trials performed and inconclusive results. More research is needed to determine the clinical efficacy of using Botox injections for knee osteoarthritis.

Fluid aspiration from a joint, called arthrocentesis, is the process of inserting a needle into a joint to remove excess fluid. The knee is the most frequently aspirated joint. Joint inflammation and swelling that occur due to osteoarthritis can produce excess synovial fluid within the knee, restricting movement and causing increased pain. Removing the fluid by aspirating the joint with a needle can help reduce pain and improve swelling.

Your doctor may place a tourniquet or compression wrap around the end of your thigh and use a local numbing agent, such as lidocaine, topically around the knee or injected within the knee joint. A needle is inserted into the knee joint at either side of the patella, and a syringe is used to pull fluid out of the knee. Fluid aspiration may be performed by itself or prior to receiving another type of injection, and generally takes 30 minutes or less to complete.

The numbing agent will typically wear off after two to four hours. It is common to have some pain or soreness for one to two days after the procedure. Pain relief from fluid aspiration can last for six months or more.

While injections can help reduce pain and inflammation, they do not cure the main problem underlying your knee pain. Physical therapy is often recommended after receiving knee injections to help improve mobility and strengthen surrounding muscles to support the knee joint to effectively manage symptoms and prevent further pain from returning.