For mild to moderate knee arthritis, cortisone works faster and PRP tends to last longer. Cortisone is an anti-inflammatory, so relief usually arrives within days. PRP starts a repair response, so it takes weeks to build. In a 2021 meta-analysis of randomized trials, PRP beat cortisone on pain, stiffness and function at three, six and nine months, with the largest gap at six and nine. The honest caveats: trials vary, the evidence is strongest before a knee is bone on bone, and the dose of PRP changes the result.
Most people asking this have already had a cortisone shot, or been offered one. The real question is what you are buying: a few quiet weeks, or a longer run of better days.
How the two compare, week by week
The first few weeks: cortisone leads
Cortisone suppresses inflammation directly, so a swollen, angry knee usually settles within days. PRP does the opposite at first: it starts a controlled inflammatory repair response, and many people are sore for a few days before they feel better. Judged at two weeks, cortisone will usually look like the better injection. That is the wrong time to judge PRP.
Three months and beyond: PRP pulls ahead
A 2021 meta-analysis in BMC Musculoskeletal Disorders pooled randomized trials comparing the two in knee osteoarthritis. PRP was better for pain, stiffness and function at three, six and nine months, with the largest difference at six and nine, and three injections about a week apart outperformed a single injection over a year. A 2025 review of 40 studies in the Journal of Clinical Medicine reached the same direction for mild to moderate arthritis, and warned that PRP preparations differ so much between clinics that results are hard to compare. More on PRP for knee osteoarthritis.
Why the dose changes the answer
PRP is not one product. A 2025 meta-analysis in the American Journal of Sports Medicine found the improvement clinically significant, and found that it lasted to twelve months only when the platelet concentration was high. That is why high-dose PRP versus standard PRP is a separate conversation, and why the first question to ask any clinic is what concentration you are getting.
Where neither injection is the answer
Most of the trial evidence sits in Kellgren-Lawrence grades one to three, which is mild to moderate arthritis on an X-ray. In advanced, bone-on-bone arthritis with deformity, the case for any injection is weaker, and the useful conversation may be about surgery or about how to spend the time before it well. Our PRP therapy evaluation starts with where your knee actually is, and we will say so if an injection is not the right tool.
When cortisone is the better choice
There are situations where cortisone is the right first injection, and a clinic that offers PRP should still tell you so.
- You need relief this week, for an event, a trip or a flare
- The knee is hot and swollen and the priority is getting the inflammation down
- Your insurance covers cortisone and cost is the deciding factor
- The arthritis is advanced and you are managing symptoms while planning surgery
- You have not yet tried the basics: strength work, load management and weight
Before you book, ask
- What grade is my arthritis, and does the evidence cover it?
- What platelet concentration will I get, and how is it measured?
- Will the injection be placed under live ultrasound?
The question to ask about cortisone
Ask how many cortisone injections you have had in that knee in the past year. If each one works for a while and then fades, that pattern is the signal the plan needs to change, not a reason to book the next one.
Frequently asked questions
Is PRP better than cortisone for knee arthritis?
For mild to moderate knee arthritis the pooled randomized trials favor PRP from about three months on. A 2021 meta-analysis in BMC Musculoskeletal Disorders found PRP better than cortisone for pain, stiffness and function at three, six and nine months, with the largest gap at six and nine. Cortisone is faster, usually within days, because it is an anti-inflammatory. So the better injection depends on what you need: fast and short, or slower and longer. In advanced bone-on-bone arthritis the case for either is weaker.
How long does a cortisone shot last in the knee?
It varies widely between people and between injections. Relief tends to arrive quickly because cortisone suppresses inflammation directly, and it tends to fade over the following weeks to months. When it fades, the arthritis underneath has not changed, which is why many people end up repeating it. If you are on your second or third injection in a year, that is a good moment to talk about a different plan.
How long does PRP take to work in the knee?
Longer than cortisone. PRP starts a repair response rather than switching inflammation off, so many people are sore for a few days and notice change over the following weeks. In pooled trials the advantage over cortisone was clearest at six and nine months, and a 2025 meta-analysis in the American Journal of Sports Medicine found function improved at one, three, six and twelve months compared with placebo. Plan for weeks and judge it at months.
Can I have PRP if I have already had cortisone?
Usually yes. Many patients come to PRP after cortisone has stopped lasting. We ask when your last injection was and time PRP around it, because cortisone suppresses the inflammatory response that PRP relies on. That is a timing question for the evaluation rather than a reason to rule PRP out.
Does PRP regrow cartilage in the knee?
The trials that compare PRP with cortisone measure pain, stiffness and function, not new cartilage, and a clinic that promises regrowth is overselling. PRP’s case is that it improves pain and function for longer than cortisone in mild to moderate arthritis. That is a real benefit, a more modest claim, and the honest one.
Is PRP covered by insurance for knee arthritis?
Usually not. Most commercial insurers treat PRP for orthopedic conditions as investigational, so the procedure is self-pay, while HSA and FSA funds typically apply. Cortisone is typically billed to insurance. That cost difference is real, and it is why we would rather you choose PRP for the right knee, at the right dose, than try it where the evidence does not support it.
Which is safer, PRP or cortisone?
Both have short risk lists in experienced hands. PRP is made from your own blood, so allergic reaction and rejection are not concerns, and the common effect is a few days of soreness. Cortisone can raise blood sugar temporarily, which matters if you have diabetes. For either injection the rare serious risk is infection, which sterile technique is designed to prevent.
Who should not get PRP for knee arthritis?
Anyone with an active infection, a significant bleeding disorder, active cancer without oncology input, or a very low platelet count should wait or be treated differently. PRP is also a weaker choice for advanced bone-on-bone arthritis with deformity. We screen for all of this at the evaluation and will tell you plainly if cortisone, physical therapy or a surgical opinion is the better next step.
Find out which injection fits your knee
Same-week evaluations with Aneesh Garg, DO, CAQ. He examines the knee, reviews your imaging, and tells you whether PRP, cortisone or something else makes sense. Every Dynamic PRP+ injection is performed by him under live ultrasound.
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1790 30th Street Suite 270 · Boulder, CO 80301 · 303-997-1733