PRP Therapy for Knee Pain: What It Is and What the Evidence Shows
How the injection is made, who it may suit and what the studies actually found.
PRP (platelet-rich plasma) therapy for knee pain is an injection made from your own blood, mainly used for mild to moderate knee osteoarthritis. Research is mixed: some trials report less pain for 6 to 12 months, while a large placebo-controlled trial found no clear benefit at 12 months. PRP does not regrow cartilage and is usually discussed only after exercise, weight management and physiotherapy.
Dr Uday Prakash Reddy is a Senior Consultant Orthopedic Surgeon (registered specialty: Orthopaedics) practising at Continental Hospitals, Financial District, Hyderabad. This article explains PRP in plain language so you can have a clearer conversation with your own doctor about whether it makes sense for your knee.
Key points
- PRP is made from your own blood and injected into the knee joint.
- It has mainly been studied in mild to moderate knee osteoarthritis.
- The evidence is mixed, and professional bodies disagree on whether it should be used.
- It does not regrow cartilage and is not a first-line treatment.
- Strengthening exercise and weight management remain the foundation of knee arthritis care.
What is PRP therapy for knee pain?
PRP therapy is an injection of platelet-rich plasma, prepared from your own blood, into the knee joint. Platelets are tiny blood cells that carry proteins called growth factors, which take part in the body's normal repair and inflammation processes. The idea is that concentrating them in the joint may ease pain and stiffness from knee osteoarthritis.
Osteoarthritis is a condition in which the smooth cartilage covering the ends of the bones slowly thins and the joint lining can become irritated. PRP is one of several injections doctors may discuss for it. Preparation methods vary widely: different kits give different concentrations of platelets and white blood cells, which is one reason study results are hard to compare (GRIP consensus, 2020).
Does PRP actually work for knee pain?
The honest answer is that it is uncertain. Some randomised trials and pooled analyses report better pain and function scores with PRP than with saline or hyaluronic acid injections for up to 6 to 12 months. However, a large, carefully blinded trial published in 2021 found no significant difference from saline at 12 months, in either pain or cartilage loss.
In that trial, called RESTORE, 288 adults aged 50 or older with mild to moderate knee osteoarthritis received three weekly injections of either leukocyte-poor PRP or salt water (saline). After 12 months, pain scores and cartilage volume on MRI changed by similar amounts in both groups (Bennell et al., JAMA 2021).
On the other side, a 2020 consensus of 15 French-speaking doctors concluded that PRP can be a symptom-relieving treatment for early to moderate knee osteoarthritis, while acknowledging that many of their recommendations rest on low-level evidence and that the group received industry funding. The same paper notes that the American College of Rheumatology and the Osteoarthritis Research Society International have advised against PRP for knee osteoarthritis, mainly because the data are inconsistent and preparations differ (GRIP consensus).
So the research does not settle the question either way. That is why PRP should be a shared decision between you and your doctor, not a default.
Who might be considered for PRP injections?
PRP is usually discussed for people with mild to moderate knee osteoarthritis whose pain continues after a fair trial of strengthening exercise, physiotherapy, weight management and simple pain relief. It is generally not a first step, and the expected benefit is lower when arthritis is severe (GRIP consensus).
Factors a doctor will usually weigh include:
- How much arthritis shows on the knee X-ray
- Whether you have already completed a structured exercise or physiotherapy programme
- Your age, weight and activity level, which may influence how well PRP works
- Whether the knee is currently swollen and inflamed (the GRIP group advises against PRP during a flare-up)
- Blood disorders, recent cancer treatment or blood-thinning medicines, which need discussion first
In my OPD at Continental Hospitals, many people who ask about PRP have not yet completed a regular strengthening programme for the thigh and hip muscles. We usually start there and review the knee again after several weeks before discussing injections.
What happens during a PRP knee injection?
A PRP injection is an outpatient procedure. A small amount of blood is drawn from your arm, spun in a centrifuge to separate the platelet-rich layer, and that plasma is injected into the knee joint, sometimes under ultrasound guidance. You normally go home the same day.
- Assessment — the knee is examined, X-rays are reviewed and other options are discussed.
- Blood draw — a small sample is taken from a vein in the arm.
- Preparation — the sample is spun so that the platelet-rich plasma separates out.
- Injection — the skin is cleaned and the plasma is injected into the joint. Some doctors use ultrasound to guide the needle.
- Aftercare — you are usually advised to go easy on the knee for a day or two, and to report increasing pain, redness or fever.
There is no agreed standard for how many injections to give. The GRIP group suggests a course may include one to three injections, spaced one to four weeks apart (GRIP consensus).
How does PRP compare with other knee injections?
Each knee injection works differently, and none of them cures osteoarthritis. Steroid injections act quickly but their effect wears off; PRP and hyaluronic acid work more slowly and their evidence is debated. The right choice depends on your knee, your other health conditions and what you have already tried.
| Injection | What it is | What the evidence says |
|---|---|---|
| Steroid (corticosteroid) | A man-made version of a natural hormone that reduces inflammation | Works quickly and can ease pain for several weeks or months (NHS) |
| Hyaluronic acid | A gel-like fluid similar to natural joint fluid | Results vary between studies and guideline advice differs |
| PRP | Concentrated platelets from your own blood | Mixed: some trials favour PRP, while a large placebo-controlled trial found no clear benefit at 12 months |
Are there side effects or risks?
Because PRP comes from your own blood, allergic reactions are unlikely. The most common effect is a short-lived increase in knee pain or swelling for a few days. As with any joint injection, there is a small risk of infection, so the procedure is done with sterile technique.
The GRIP review reports post-injection pain or swelling in fewer than 1 in 10 people across studies, and notes that brief symptoms such as nausea, headache or feeling faint have occasionally been described (GRIP consensus).
What else helps knee osteoarthritis pain?
Exercise is one of the most important treatments for knee osteoarthritis, whatever your age or fitness. Strengthening the thigh and hip muscles, staying active and reaching a healthy weight reduce the load on the knee. Supportive footwear, a walking stick and physiotherapy can also help day-to-day comfort (NHS).
- Regular strengthening and general fitness exercise, ideally planned with a physiotherapist
- Gradual weight loss if you are overweight
- Shock-absorbing footwear or insoles
- Hot or cold packs during flare-ups
- Pain relief advised by your doctor
Our page on non-surgical orthopaedic treatment explains these options in more detail. If they do not help and daily life is badly affected, surgery such as knee replacement may be discussed.
When should you see an orthopaedic doctor about knee pain?
See a doctor if knee pain lasts more than a few weeks, keeps coming back, wakes you at night, or limits walking and climbing stairs. Get the knee checked sooner if it becomes hot, red and swollen, if you have a fever, or if the pain started after a fall or a twisting injury.
If your pain began with a sports injury rather than gradual wear, see our page on knee arthroscopy and sports injury care.
Sources
- NHS – Osteoarthritis: treatment and support
- Bennell KL et al. Effect of intra-articular platelet-rich plasma vs placebo injection on pain and medial tibial cartilage volume in patients with knee osteoarthritis: the RESTORE randomized clinical trial. JAMA. 2021;326(20):2021–2030.
- Eymard F et al. (GRIP). Intra-articular injections of platelet-rich plasma in symptomatic knee osteoarthritis: a consensus statement from French-speaking experts. Knee Surg Sports Traumatol Arthrosc. 2021;29(10):3195–3210.
Medically reviewed by Dr. Uday Prakash Reddy, MBBS, MS (Orthopedics), Senior Consultant Orthopedic Surgeon, Continental Hospitals. This article is general health information and does not replace a consultation or medical advice. Consult a qualified doctor if knee pain, swelling or instability persists.
About the Author
Dr. Uday Prakash Reddy
Senior Consultant Orthopedic Surgeon at Continental Hospitals, Hyderabad, with over 24 years of experience in orthopedics, arthroscopy and joint replacement.