Do PRP Injections Actually Work for Knee Arthritis?
A new meta-analysis of 18 controlled trials says PRP works for knee arthritis — with a catch: platelet concentration. Who benefits, how long it lasts, and what to ask.
PRP injections for knee arthritis are one of the most common things I get asked about. For a while, the honest answer was that the evidence was mixed.
A new meta-analysis just published in the American Journal of Sports Medicine — 18 controlled trials, nearly 2,000 patients — changes that. The short answer: PRP works. But there's a catch.
What PRP does
Platelet-rich plasma is made from your own blood. We draw a small sample, spin it to concentrate the platelets, and inject that directly into the knee. Platelets carry growth factors that reduce inflammation and signal tissue repair. Unlike steroids, which mask symptoms, PRP is trying to address the underlying biology of the arthritic joint.
What the study found
Across 18 randomized controlled trials, PRP consistently outperformed placebo on both pain and function — and not just statistically. The researchers measured whether the improvement crossed the MCID (minimum clinically important difference), the threshold at which patients actually feel better in their daily lives. PRP cleared that bar for function at every follow-up point, including 12 months.
But the most important finding was in a subgroup analysis by platelet concentration:
| High-platelet PRP (over 1M platelets/µL) | Low-platelet PRP | |
|---|---|---|
| Pain | Relief at 3, 6 and 12 months | Never cleared the meaningful threshold |
| Function | Improved through 12 months | Benefit faded by 12 months |
Low-platelet PRP — made with lower-quality centrifugation protocols — never produced pain relief that patients could meaningfully feel. High-platelet PRP maintained benefit at a full year. This likely explains years of contradictory PRP research: the studies were comparing good PRP to bad PRP without realizing it.
Who is a good candidate?
- Best fit: mild to moderate knee arthritis (not yet bone-on-bone) with pain and functional limitation. PRP can meaningfully reduce symptoms and potentially slow progression.
- Not the right tool: severe, end-stage arthritis with significant joint space loss. At that point, a partial or total knee replacement will do far more than any injection.
- Ask before you go: "What platelet concentration do you use, and how is it verified?" A provider who can't answer that may not be offering the preparation that actually works.
Frequently asked questions
How long does it last?
High-platelet PRP showed meaningful benefit at 12 months. Many patients are most improved at 3–6 months and opt for repeat injections when symptoms return.
Is it covered by insurance?
Most plans still classify PRP as investigational for knee arthritis. It is typically an out-of-pocket expense for now.
Is it safe?
Yes. Because it's made from your own blood, the risk of allergic reaction or infection is very low. Temporary soreness at the injection site is the most common side effect. No serious adverse events were reported across these 18 trials.
If you have knee arthritis and want to understand all your options — injections, partial knee replacement, total knee replacement — I'd encourage you to come in. The right treatment depends on where you are in the process, and that's exactly the conversation I want to have.
This article is general education, not medical advice for your situation. Every knee and hip is different — talk with your own doctor about your care.