Overview
Injections are among the most common and effective nonoperative treatments for knee pain and arthritis. There are two primary types of injections I use around the knee: cortisone injections and viscosupplementation injections. Cortisone works primarily by reducing inflammation. Viscosupplementation works differently by improving the lubricating properties and viscosity of the joint fluid. Both can be effective, but they work on different timelines and are often most useful at different stages of treatment.
Knee Cortisone Injections
Cortisone injections are most commonly placed directly into the knee joint to treat arthritis and other inflammatory conditions. Most of my cortisone injections contain a combination of Depo-Medrol and Kenalog, providing both intermediate- and longer-acting corticosteroid effects. These medications are mixed with a local anesthetic such as Lidocaine or Marcaine, which provides immediate temporary pain relief. One of the advantages of cortisone is its simplicity. The injections are relatively inexpensive, do not require insurance pre-certification, and can usually be performed during the initial office visit.
Immediately after the injection, the local anesthetic typically provides one to two hours of numbness. As it wears off, patients may experience a few days of mild to moderate soreness before the cortisone begins providing its longer-lasting effect. Cortisone does not heal the underlying arthritis or other structural problem. Instead, it decreases the inflammation surrounding the problem, and that inflammation is often a major source of the pain. The medication generally remains active for approximately 2-3 months, although many patients experience improvement well beyond that period if the inflammation has been successfully reduced. Injections can also provide useful diagnostic information. A good response helps confirm that the knee joint itself is a significant source of the patient's symptoms.
Viscosupplementation Injections
Viscosupplementation injections, sometimes referred to as gel injections, are used specifically for knee arthritis. Rather than primarily decreasing inflammation, viscosupplementation improves the lubricating properties and viscosity of the fluid within the knee. Common products include Synvisc, Durolane, Monovisc, Hyalgan, and others.
Unlike cortisone, viscosupplementation does not work immediately. It generally takes approximately 4-6 weeks to reach its full effect, but when successful, relief may last 4-6 months or longer. These injections frequently require insurance pre-certification, so patients commonly return for a second visit once approval has been obtained. They do not affect blood sugar or have significant medication interactions, although a very small percentage of patients may develop a temporary inflammatory reaction following an injection, particularly after repeated courses.
Using Cortisone and Viscosupplementation Together
I often think of cortisone as a spot treatment and viscosupplementation as a maintenance treatment. For a patient who is significantly uncomfortable or just beginning injection treatment, I often use the two sequentially. I start with a cortisone injection because it works relatively quickly and can begin controlling the pain and inflammation early.
Approximately 3-4 weeks later, I may follow with viscosupplementation. During those first several weeks, the cortisone is providing most of the relief while the viscosupplementation is gradually beginning to work. By the time the effect of the cortisone starts to fade, the viscosupplementation may be reaching its full effect. The goal is to create a smoother and more sustained period of improvement rather than allowing the pain to repeatedly rise and fall between treatments. For that reason, I generally do not like starting with viscosupplementation alone in a patient who is very uncomfortable. It simply takes too long to begin working.
Safety
Knee injections are generally extremely safe and are among the least painful injections performed in orthopedics. Cortisone has very few interactions with other medications. The most important consideration is in patients with diabetes, because blood sugar can increase significantly for approximately 2-3 days after a cortisone injection. I encourage diabetic patients to monitor their blood sugar, but not overreact to the elevation because it is a temporary spike that will return to normal.
The risk of infection following an injection is extremely low. In nearly 30 years of practice and tens of thousands of injections, I have encountered this complication only once. Although uncommon, an infection can have significant consequences, particularly around a prosthetic joint. When surgery is anticipated, I generally prefer to wait approximately 6-8 weeks before arthroscopic surgery and approximately 3 months before knee arthroplasty following a cortisone injection.