A cortisone shot delivers a powerful anti-inflammatory medication directly into your knee joint, reducing swelling and pain that can last from several weeks to several months. It’s one of the most common treatments for knee pain caused by osteoarthritis, bursitis, and other inflammatory conditions, and it works by calming the immune response inside the joint itself rather than through your whole body.
How It Works Inside the Joint
When your knee is inflamed, whether from arthritis wearing down cartilage or from an overuse injury irritating the surrounding tissue, immune cells flood the area and release chemicals that cause swelling, stiffness, and pain. A cortisone shot puts a concentrated dose of corticosteroid right where this inflammation is happening, suppressing that immune response at the source. Because the medication goes directly into the joint space rather than traveling through your bloodstream, it can work at much higher local concentrations than an oral anti-inflammatory pill while producing fewer body-wide side effects.
When Pain Relief Kicks In
Don’t expect immediate results. It can take up to a week for the cortisone to reach full effect, and some people experience a temporary flare of pain and swelling in the first 24 to 48 hours after the injection. This post-injection flare is common and not a sign that something went wrong.
Once the medication takes hold, relief typically lasts anywhere from a few weeks to a few months. The range is wide because it depends on how much inflammation is present, the underlying condition, and individual factors. Some people get three or four months of significant relief; others notice the effect wearing off after six weeks. The shot doesn’t fix the underlying problem. It buys time with less pain, which can make it easier to do physical therapy or stay active.
What the Injection Feels Like
The procedure itself takes only a few minutes. Your doctor cleans the skin around your knee and may numb the area with a local anesthetic. The cortisone is then injected through a needle into the joint space. Some providers use ultrasound imaging to guide the needle, which improves accuracy and tends to produce better pain relief compared to injections placed by feel alone. You might feel pressure during the injection, but sharp pain is uncommon. If your knee has excess fluid, your doctor may drain some of it before injecting the cortisone.
Afterward, you can typically walk and bear weight right away, though it’s wise to take it easy for the rest of the day. Most doctors recommend avoiding high-impact activities like running or jumping for at least 48 hours to let the medication settle and reduce the chance of a flare.
How Often You Can Get One
This is where guidelines get less clear-cut. Most orthopedic surgeons use a minimum interval of three months between repeat injections in the same knee, though some providers are comfortable with shorter gaps. A 2025 consensus from several pain medicine societies suggests a minimum of two to three weeks between injections, with intervals of up to three months being more typical. The key principle: if a shot isn’t providing meaningful relief anymore, repeating it won’t help. The series should stop when pain relief plateaus.
The concern with frequent injections isn’t just diminishing returns. A landmark trial found that patients who received cortisone every three months for two years lost slightly more cartilage than those who received placebo injections. The difference was small, about 0.05 millimeters per year. Given that the cartilage in your knee is roughly 3 to 5 millimeters thick, it would take roughly a decade of injections every three months to thin cartilage by about 12%. That’s measurable, but it puts the risk in perspective. For someone managing severe pain while waiting for a knee replacement, this tradeoff may be entirely reasonable. For someone with mild arthritis looking at decades ahead, it’s worth discussing alternatives.
Side Effects to Watch For
The most common side effect is a short-term flare: increased pain, swelling, and irritation at the injection site for up to two days. Icing the knee and resting usually manages this. If swelling, redness, or worsening pain persist beyond 48 hours, that could signal an infection, which is rare but requires prompt attention.
If you have type 2 diabetes, expect your blood sugar to rise for a few days after the injection. Studies using continuous glucose monitors show that average blood sugar levels climbed from about 136 mg/dL before injection to 159 mg/dL in the first three days, then returned to baseline. Some patients saw brief spikes above 250 or even 350 mg/dL, though these episodes were short-lived. If you manage diabetes, plan to monitor your glucose more closely for two to three days after the shot and discuss adjustments with your doctor beforehand.
What a Cortisone Shot Won’t Do
Cortisone reduces inflammation. It does not rebuild cartilage, repair a torn meniscus, or reverse arthritis. It’s a symptom management tool, not a cure. For many people, that’s exactly what they need: enough pain relief to sleep better, walk comfortably, or participate in physical therapy that strengthens the muscles supporting the knee. Used strategically, a cortisone shot can be the bridge between a painful flare and longer-term management through exercise, weight loss, bracing, or eventually surgery if the joint deteriorates further.