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Knee injections are a popular treatment for osteoarthritis, but studies don't support their use

Straight Healthcare
December 2021
knee receiving an injection
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There is no question that knee injections are a popular treatment for knee pain. Patients who complain of chronic osteoarthritic pain almost always receive one or more steroid injections, and some are given hyaluronic acid (Synvisc®). A third type of injection, platelet-rich plasma, is becoming more popular. While patients may like the fact that their complaint received active and prompt treatment, there is little evidence these shots actually do anything. We break it down for you below.

First, let's take a look at the most popular treatment, steroid injections. Steroids injected into the knee joint are supposed to suppress inflammation and ease pain. Several studies have compared these injections to placebo. In one, 100 patients were given a steroid injection or saline. At 14 weeks, there was no significant difference in pain or function outcomes between the groups. [SH review ] In another study, 140 patients were randomized to steroid injections or placebo every 12 weeks for 2 years. Over the course of the study, there was no significant difference in pain or function outcomes, but the steroid group lost significantly more cartilage in their knee, as measured by MRI. [SH review] In a third study, 156 patients received either steroid injections or physical therapy over a year. In the end, physical therapy was superior to steroids for both pain and function outcomes. [SH review] The American Academy of Orthopaedic Surgeons (AAOS) guidelines state that "intra-articular corticosteroids could provide short-term relief for patients with symptomatic osteoarthritis of the knee." For their evidence, they cite some strange studies - most involve active controls or steroids being added to other drugs, one study doesn't even have a steroid arm, and a study they called "high quality" was retracted. Perhaps the AAOS doesn't want to contradict its members who routinely perform these shots, but the evidence is clear, steroid shots are ineffective and may even be harmful.

The second most popular treatment is hyaluronic acid injections, more commonly known as Synvisc®. Hyaluronic acid is a gel-like substance that is purported to "lubricate and cushion" the knee joint. A study that randomized 99 patients to Synvisc® or steroid injections found no significant difference between the treatments for pain and function outcomes over 6 months. [SH review] One Synvisc® injection costs around $1000, whereas a vial of steroid costs about $10. The AAOS states that "hyaluronic acid intra-articular injection(s) is not recommended for routine use in the treatment of symptomatic osteoarthritis of the knee."

The last injection type is platelet-rich plasma (PRP), where blood is taken from a patient and centrifuged so that it separates into layers of red blood cells, platelets, and plasma. The platelet layer is removed and mixed with a small amount of plasma to produce platelet-rich plasma. The sample is sometimes treated with chemicals to make the platelets lyse and release growth factors. Proponents of this therapy contend that bloodborne cytokines and growth factors stimulate and accelerate healing. A study that compared PRP injections to placebo in 288 people with knee osteoarthritis found that PRP was no more effective than placebo over 12 months. [SH review] The AAOS states that "Platelet-rich plasma (PRP) may reduce pain and improve function in patients with symptomatic osteoarthritis of the knee." This is surprising given that most placebo-controlled trials involving PRP have found it has no effect on joint and soft tissue disorders.

Patients with knee pain should skip the injections and focus on leg strengthening and weight loss if needed.