An intra-articular injection, by definition, is an injection administered directly into a joint. The medication is actually injected into the joint space for the purpose of relieving joint pain. Corticosteroids (steroids) were the first commonly-used substances injected into painful joints. Aside from intra-articular steroid injections, there are also intra-articular hyaluronic acid injections and intra-articular local anesthetics.
When Is an Intra-articular Injection Given?
An intra-articular injection is typically given when a joint with localized pain (acute or chronic) has not responded to or stops responding to oral pain medication, oral anti-inflammatory medication, or other conservative treatment options. Intra-articular injections have been a treatment option for decades. Intra-articular steroid injections, specifically, have been used to treat painful joints since the 1950s.
How Do the Injections Work?
Intra-articular steroid injections have anti-inflammatory properties and work by decreasing inflammation. Technically, intra-articular steroids decrease the number of lymphocytes, macrophages, and mast cells, thereby reducing phagocytosis, lysosomal enzyme release, and the release of inflammatory mediators (interleukin-1, leukotrienes, and prostaglandins). By reducing inflammatory mediators, pain is decreased too.
Some patients with non-inflammatory arthritis, such as osteoarthritis, also are helped by intra-articular steroid injections. Also, intra-articular steroids may protect joint cartilage by reducing metalloproteinase synthesis (which acts to degrade cartilage).
Hyaluronan injections are an attempt to improve the lubrication of the joint, reduce pain, and improve range of motion. When there is cartilage damage, synovial fluid changes and loses its ability to lubricate the joint. There are at least five products now marketed as hyaluronates.
Local anesthetic injections are sometimes given with intra-articular steroid injections. They are said to provide a temporary analgesic effect on their own accord. But, according to AAOS Now from June 2010, researchers reported that intra-articular local anesthetics have a negative effect. Over time, they reduce chondrocyte (the only cells found in cartilage) density. The study included animals, though, not humans.
What Are the Benefits and Risks?
Possible adverse reactions associated with intra-articular injections include infection and local site reactions. There is also concern about using steroid injections on diabetic patients since they may have transient increases in blood glucose.
Obviously, the most well-known concern is potential joint destruction that comes with repeated steroid injections. Experts recommend three months between steroid injections in the same joint. Hyaluronan injections are administered as a series of injections over 3 to 5 weeks.
Why Aren't Intra-articular Injections Equally Effective?
Different doctors use different preparations of steroids. Hydrocortisone is considered weak and short-acting. Methylprednisolone preparations can work for 1 to 2 weeks. Kenalog and Aristocort (preparations of triamcinolone) can work for 4-16 weeks. Celestone (a preparation of betamethasone) can work for 2 to 8 weeks. Aristopan (another preparation of triamcinolone) can take a week to work and lasts for months. Aside from the preparation used, your doctor's technique may contribute to whether an injection is effective or ineffective.
Hyaluronan injections are used to buy time before a knee replacement surgery. They also are given to people who do not tolerate steroids and do not benefit from oral pain or anti-inflammatory medications. In some cases, patients get up to one year of relief after going through the 3 or 5 week sessions. If the benefit wanes, hyaluronan can be repeated.
About 20% of patients who have hyaluronan injections achieve a benefit. Patients who are going to respond to hyaluronan tend to do so in one or two weeks. But, in terms of how effective hyaluronan injections are, there is no evidence that they work better than oral naproxen.
All About Osteoarthritis. Joint Injections With Steroids. P.171. Nancy E. Lane MD and Daniel J. Wallace MD. Oxford Univeristy Press. 2002.
Intra-Articular Injections. William Lavelle MD, et al. Anesthesiology Clinics. 25(2007) 853-862.
Raising a Red Flag on Intra-articular Injections. An Interview With Constance R. Chu, MD. Mary Ann Porucznik. AAOS Now. June 2010.