The most common cause of knee arthritis is osteoarthritis — the progressive wearing of cartilage, which exposes bone-on-bone contact and leads to inflammation, pain, and swelling. Lifestyle factors are the most effective treatment: regular exercise, a healthy weight, and a balanced diet. But cortisone has a limited effect and may cause harm, and surgery is a last resort. So many people now consider a PRP injection for the knee. Here’s what PRP injections for knees involve, and whether they work.
What is PRP?
Platelet-rich plasma (PRP) is taken from your own blood and concentrated so that the plasma contains a high number of platelets. Once injected into the knee, the platelets release growth factors that reduce inflammation and improve the joint environment. (For the general background — systems, safety, and preparation — see our PRP therapy FAQ.)
Does PRP work for knee arthritis?
This is where the evidence for PRP is strongest. Twenty-three randomised trials show PRP is better than other injections for knee arthritis. For the knee specifically, we generally favour a moderate platelet concentration with a low white-cell count, which tends to cause less post-injection flare.
What is the optimal dose of platelets for the knee?
We don’t know for certain. A 2021 study suggested that a 10-billion-cell dose is optimal, but it was methodologically flawed. A 2024 study found that a one-time higher dose of approximately 5 billion platelets was more effective than 2.5 billion, though the study was short-term (6 months) and included few low-grade arthritis subjects.
The practical takeaway: aim for a platelet dose approaching 4–5 billion. With standard PRP, that’s achieved over 2–3 injections. Second-generation systems such as Arthrex ACP Max deliver a higher dose (around 5–12 billion platelets) in a single injection.
Does PRP reverse knee joint damage?
Generally, no. PRP changes the joint environment and reduces pain, but there’s no good evidence that it regenerates cartilage. Research into whether PRP has any regenerative effect is ongoing.
How many PRP injections do I need for knee arthritis?
With standard PRP, we usually recommend 2–3 injections about two weeks apart to reach an effective platelet dose — a course tends to outperform a single standard injection and can last up to around 18–24 months. Where Arthrex ACP Max is used, the higher dose is delivered in a single injection.
Are ultrasound-guided PRP injections better for the knee?
Yes. Even in experienced hands, a blind knee injection is only about 80% accurate — so 1 in 4 misses the target without imaging. We use ultrasound rather than X-ray because it’s less expensive and avoids radiation exposure.
[KEEP THE EXISTING VIDEO HERE — /wp-content/uploads/2022/07/My-Movie.mp4 — ultrasound-guided knee PRP footage; a strong first-hand E-E-A-T asset.]
How long do I rest after a knee PRP injection?
Avoid impact exercise for at least a week after a knee PRP injection, though this varies with what’s injected.
Side effects of PRP injections for the knee
Any procedure carries risk, but because we use your own blood, the risks are lower than with cortisone. They include infection (about 1 in 10,000), a pain flare, and rupture (rare). A flare is common and can last a few weeks — ice and paracetamol or codeine help. Occasionally, an injection worsens the problem in about 1–2% of cases.
How common is knee pain after a PRP injection?
A flare is common but usually settles within 1–2 weeks. Leucocyte-poor (low white-cell) PRP causes less post-injection knee pain than leucocyte-rich PRP, which is why we favour it for the knee.
How long does the effect last?
For knee arthritis, we estimate the benefit lasts about 12–18 months, and up to around 24 months with a course of injections.
How much do PRP injections for knees cost?
PRP can range from £300 to £2,000 per injection — but a higher cost doesn’t mean a better result. For example, N Stride PRP requires one injection but costs £2,000, and studies on N Stride have shown little difference compared with other PRP systems. Dr Masci offers higher-concentration Arthrex ACP Max for £1,350, and standard PRP from £510 (first injection). Review the fees here.
Can you combine PRP and hyaluronic acid?
Possibly to advantage. Hyaluronic acid improves knee arthritis pain and function but is generally less effective than PRP. However, recent studies suggest combining the two may beat either alone, with pain reduction at both 3 and 12 months — though we await further evidence before routinely recommending it. See combining PRP and hyaluronic acid.
Is PRP better than cortisone for the knee?
Recent evidence suggests PRP is superior to cortisone, most clearly between 6 and 9 months in moderate-to-severe arthritis, with around twice the effect. PRP also isn’t harmful to cartilage, unlike cortisone. See cortisone vs hyaluronic acid to compare the options.
Are stem cells more effective than PRP for the knee?
Probably not. So-called “stem cells” from fat or bone marrow are largely pericytes. They may slightly improve the joint environment, but a review found little evidence for their cost-effectiveness, and a study comparing stem cells with PRP in knee arthritis found no difference. We need more evidence before calling stem cells superior to PRP.
Frequently asked questions about PRP injections for knees
Do I need to prepare for a knee PRP injection?
Yes — stay well hydrated (1–1.5 litres of fluid on the day), and avoid aspirin or ibuprofen for at least ten days before the procedure (and for a couple of weeks after the last injection), as they reduce PRP’s effect.
Can I have PRP if I’m on a blood thinner such as warfarin?
Yes. Warfarin doesn’t affect PRP, but tell your doctor, as you have a slightly higher bleeding risk after the procedure.
Is PRP worth it for bone-on-bone knee arthritis?
PRP tends to work better in mild-to-moderate arthritis than in severe, bone-on-bone joints, where the benefit is smaller, and a joint replacement may eventually be needed. An assessment helps set realistic expectations.
Final word from Sport Doctor London about PRP injections for the knee
Regenerative medicine is a young and fast-growing field, and we take a common-sense, cautious approach. We currently use low-white-cell PRP for knee arthritis, combined with exercise — the evidence here is strongest — while remaining more cautious about PRP for other joints until the evidence grows.
To discuss whether PRP suits your knee, contact Dr Masci’s team here or call +44 (0) 203 488 0350.
How can I buy these injections.
You need to see a doctor who performs these injections preferably under ultrasound-guidance
What is the treatment for recovery after the injection
please see my blog on the treatment of osteoarthritis including exercise: https://sportdoctorlondon.com/no-cartilage-in-knee/
Generally, I recommend rest from impact activity (running) for 1 week.
please see my blog on the treatment of osteoarthritis, including exercise: https://sportdoctorlondon.com/no-cartilage-in-knee/
Generally, I recommend rest from impact activity (running) for one week.
Dear Dr Masci,
I have been told by my orthopedics surgeon that I need a total knee replacement.
Could you please recommend a highly skilled doctor in Houston, Texas, who administers PRP injections using ultrasound?
The number of local doctors/clinics who claim to do this treatment is overwhelming, and I need help finding the right doctor.
Thank you very much.
Hi Pamela,
Unfortunately, I don’t have any contacts in Texas.
LM
I had one PRP injection four years ago in my left knee for OA that made me quit hockey at age 70 because my knee was constantly swollen and painful every hockey season.
I started with two Hyaluronic acid injections which lost effectiveness after three months each, then took PRP. My knee never swells, is pain free and I stopped wearing knee braces when active. I can navigate stairs normally now too.
Hi Gene, Thanks for posting. I’m pleased you’ve had a great response from one PRP injection. I’d consider a top up PRP if you’re knee symptoms return. All the best LM