Start here

A blood-derived product, not a brand name.

PRP is made by drawing blood, concentrating platelets in a smaller volume of plasma, and injecting the prepared product into the knee. It is not a stem-cell treatment, and the letters “PRP” do not tell you the dose or full composition.

What it is

A product made from your own blood that contains concentrated platelets and signaling proteins.

What it may do

Reduce symptoms and improve function for a period of time in selected patients.

What it cannot promise

Cartilage regrowth, disease reversal, or avoidance of future knee replacement.

Current evidence

Benefit is possible, but response is not uniform.

A 2025 meta-analysis of 18 placebo-controlled trials involving 1,995 patients found clinically meaningful improvement in Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) scores across follow-up, with pain improvement most evident at three and six months. Higher platelet concentration was associated with better results.

That pooled result does not erase important negative trials. In the 288-patient RESTORE trial, three weekly leukocyte-poor PRP injections did not improve 12-month pain or medial tibial cartilage volume compared with saline. Other sham-controlled trials have reported benefit. Taken together, the evidence suggests that some PRP protocols help some patients, but we still cannot reliably predict which preparation or patient will respond.

What pooled studies show

Across many trials, average pain and function outcomes generally favor PRP over placebo or common comparators.

What negative trials show

Several well-designed saline-controlled studies have found little or no benefit, including RESTORE.

Clinical meaning

A favorable average does not predict an individual response, and the preparation used in one study may not match another.

Why apparently similar trials can disagree

Studies vary in platelet dose, injected volume, leukocytes and neutrophils, red blood cell contamination, activation, number and timing of injections, image guidance, rehabilitation, osteoarthritis severity, and outcome measurement.

Product quality

PRP is a dose, not just a label.

A statement such as “four times concentrated” is incomplete unless the starting count, final concentration, and injected volume are known. Total deliverable platelets provide a more useful description of what reaches the knee.

Total platelet dose

Final platelets per microliter × injected volume in milliliters × 1,000 = total deliverable platelets.

For example, 1.25 million platelets per microliter in 8 mL yields 10 billion total platelets.

Core dose

Final platelet concentration, injected volume, and calculated total deliverable platelets.

Cell composition

Leukocytes, neutrophils, and red blood cell contamination can distinguish biologically different products.

Protocol

Preparation method, activation, device settings, injection number, guidance, and rehabilitation plan.

Why the 10-billion target deserves attention

01
Concentration signal
The 2025 Bensa meta-analysis found greater clinical improvement in higher-concentration PRP groups, although concentration is not the same as total dose.
02
Direct randomized signal
A 2024 trial reported better three- and six-month outcomes with about 5.65 billion platelets in 8 mL than with about 2.82 billion in 4 mL. Dose and volume changed together, so the trial does not isolate platelet dose alone.
03
Ten-billion clinical signal
A 2021 randomized study found that a leukocyte-depleted product delivering about 10 billion platelets produced better 12-month outcomes than hyaluronic acid. It was not a dose-comparison trial and did not establish a minimum effective dose.
04
Current best-practice guidance
The American Academy of Physical Medicine and Rehabilitation's (AAPM&R) 2026 guidance identifies at least 10 billion total deliverable platelets as a best-practice target for knee osteoarthritis.

Bottom line

Ten billion is an evidence-informed target, not a proven biological cutoff.

Higher delivery may matter, and current AAPM&R guidance now supports a target of at least 10 billion platelets. The available trials do not prove that 9.9 billion cannot work, that 10 billion will work, or that more is always better.

Questions worth asking about any PRP product

What is being delivered? Ask for final platelet concentration, injected volume, and total platelet dose.
What else is in it? Ask whether the clinician measures or otherwise characterizes leukocytes, neutrophils, and red blood cells.
Why this schedule? Ask why one injection or a series is being recommended for this diagnosis.
How will it be judged? Define the functional goal, reassessment timing, rehabilitation plan, and total cost.

Patient selection

Who may reasonably consider PRP?

PRP is generally considered after the diagnosis is clear and foundational treatment has not provided enough relief. The decision should start with the knee and your goals, not with the availability of an injection.

Best supported by evidence

Persistent symptomatic mild-to-moderate knee osteoarthritis after an appropriate exercise, rehabilitation, and symptom-management plan.

Realistic treatment goal

Improve pain and function enough to support meaningful activity, while understanding that nonresponse is possible.

Lower confidence or defer

End-stage disease, active infection, a hot, unexplained swollen knee, major diagnostic uncertainty, or expectations of cartilage regrowth.

Age, disease severity, alignment, metabolic health, medications, prior treatment, and activity demands may influence the discussion. No single test reliably predicts who will benefit.

Before, during, and after

Plan the recovery before the blood draw.

PRP instructions vary because products and study protocols vary. The written instructions from the clinician performing the procedure should take precedence, especially when another clinician prescribes an essential medicine.

Never stop a prescription medicine on your own

Do not stop aspirin, an anticoagulant, an antiplatelet medicine, corticosteroid, antibiotic, prescription omega-3, or any other prescribed treatment without coordination between the clinician performing PRP and the clinician who prescribed it. If an essential medicine cannot be interrupted safely, postponing an elective PRP procedure may be safer than interrupting treatment.

Before your PRP injection

Confirm the diagnosis and target
Review the history, examination, and appropriate imaging. A newly hot, swollen knee, active infection, or major diagnostic uncertainty should be evaluated before an elective injection.
Send a complete medication list
Include every prescription, over-the-counter medicine, topical pain product, vitamin, and supplement, with the dose and reason for use. Report recent cortisone injections and all steroid use.
Call if health changes
Contact the clinic for fever, chills, a skin or dental infection, a wound near the knee, recent invasive dental work, or antibiotic treatment. Do not stop an antibiotic. The procedure may need to be rescheduled.
Prepare for the blood draw
Unless told otherwise, do not fast. Eat a normal light meal and drink water. Avoiding a high-fat meal for 24 hours and alcohol for 48 hours is a low-certainty consensus recommendation, not a proven outcome requirement.

Medication and supplement review

Know what to discuss, and what not to stop.

Ibuprofen, naproxen, diclofenac, and other nonsteroidal anti-inflammatory drugs (NSAIDs). Your clinician may ask you to avoid these before and after PRP because they can inhibit platelet function. Exact timing is not proven and depends on the medicine and why you take it. Ask about topical NSAIDs too.
Aspirin and antiplatelet medicines. Avoid starting aspirin for pain unless instructed. If aspirin, clopidogrel, or another antiplatelet was prescribed for your heart, brain, blood vessels, or a stent, do not stop it. The prescribing and PRP clinicians must coordinate.
Anticoagulants or blood thinners. Report warfarin, apixaban, rivaroxaban, dabigatran, edoxaban, enoxaparin, and similar medicines. Joint injection is generally a low-bleeding-risk procedure, but individual risk and PRP candidacy still require review.
Acetaminophen. This is often the preferred non-anti-inflammatory pain option when medically safe. Follow the label or clinician's dose, and check first with liver disease, heavy alcohol use, or another medicine that already contains acetaminophen.
Corticosteroids and antibiotics. Report recent cortisone injections and oral, injected, inhaled, or topical steroid use. A recent injection into the target joint may change timing. Never stop chronic steroids suddenly. Active bacterial infection should resolve before elective PRP.
Supplements. Report concentrated garlic, turmeric or curcumin, ginkgo, high-dose vitamin E, fish oil or omega-3, and other supplements. Some can affect platelet or bleeding pathways, but no supplement has been shown clinically to improve or reduce the effect of PRP.

What is known about timing?

Some expert consensus protocols use a cautious period off NSAIDs before and after PRP. Pharmacology studies show that platelet inhibition varies substantially by medicine, and no human outcome trial proves that one period off medication improves PRP results. The individualized written plan is more important than a universal number.

What to expect during the procedure

Blood is drawn and processed, the skin is cleaned, and the prepared PRP is injected. Ultrasound guidance may be used to visualize the knee and needle. The visit may take longer than the injection itself because product preparation requires time.

After your PRP injection

Use relative rest for the first 24 hours
Normal necessary walking is usually reasonable as tolerated, but avoid strenuous exercise and heavy loading. Do not remain completely inactive unless the care team gives a specific reason.
Expect a possible temporary flare
Soreness, stiffness, or swelling can occur and may feel worse before it feels better. It should begin improving over the next several days.
Follow the provided pain plan
Unless your clinician directs otherwise, avoid NSAIDs during early recovery. Many knee protocols use one week and some use two weeks, but direct outcome evidence is absent. Acetaminophen may be used when approved and medically safe.
Resume loading gradually
No single post-PRP knee program has been validated. Restore motion, walking, strength, and higher-demand activity in stages. Tendon and ligament PRP require different loading schedules.

Bandage and water

Keep the puncture site clean and follow the bandage and shower instructions you received. Avoid soaking until the puncture has closed.

Cooling and heat

Brief use of a cold pack may ease discomfort, but whether ice changes PRP biology or outcomes is unknown. Avoid extreme heat or soaking the puncture site until the skin has closed.

Driving

Do not drive after a sedating medicine, lightheadedness, temporary numbness, or if you cannot steer and brake firmly without hesitation. Arrange a ride if there is any doubt.

Evidence versus clinic protocol

Temporary flare, relative rest without immobilization, medication review, and postponing elective PRP during active infection have broad support. Exact NSAID windows, recent steroid timing, alcohol and diet guidance, ice, bandage, shower, driving, and rehabilitation details rely more heavily on consensus or local protocol.

One injection or a series?

The best number and spacing of injections remain unsettled. More injections are not automatically better. Product, evidence, burden, cost, response, and the overall treatment plan should guide the choice.

When to seek urgent care after an injection

Seek same-day urgent medical assessment and contact the injecting team for fever or chills, drainage, spreading redness or warmth, rapidly increasing swelling, pain that is severe or progressively worsening rather than settling, significant bleeding, new weakness or numbness, or inability to bear weight. Do not wait for a routine reply. Call 911 for trouble breathing, fainting, chest pain, confusion, severe illness, or another medical emergency.

Guideline context

Recommendations have evolved, but they still differ.

Professional groups review different evidence, use different thresholds for clinical importance, and publish at different times. These include physical medicine and rehabilitation, orthopaedic surgery, federal health systems, and a European sports medicine and cartilage consensus group. The date and scope of a recommendation matter.

AAPM&R, 2026

Recommends considering PRP after failed conservative care in mild-to-moderate knee osteoarthritis, with product characterization and a target of at least 10 billion platelets.

AAOS, 2021

States that PRP may reduce pain and improve function, but rates the recommendation as limited.

VA/DoD, 2026

Finds insufficient evidence to recommend for or against PRP because the research remains heterogeneous and very uncertain.

ESSKA-ICRS, 2024

Supports selected use after conservative care has failed in patients with Kellgren-Lawrence (KL) grade 0 to 3 disease, but not as first treatment or for KL grade 4.

Guidelines inform the conversation. They do not replace individual diagnosis, medical screening, cost discussion, and shared decision-making.

Cost and alternatives

Compare PRP with the full range of treatment options.

PRP is often not covered by insurance and may involve substantial out-of-pocket cost. Coverage, authorization, product availability, and pricing should be confirmed with the clinic and health plan before treatment.

Foundational care. Education, progressive exercise, rehabilitation, activity planning, and weight-management support when relevant. Choose the beginner knee osteoarthritis program or the advanced progression when appropriate.
Medication options. Topical or oral medicines when appropriate for your health history.
Other injections. Corticosteroid or hyaluronic acid may be discussed selectively, with different evidence, timing, risks, and coverage.
Surgical consultation. Appropriate when substantial symptoms and limitations persist or advanced disease changes the balance of options.

Compare hyaluronic acid for knee osteoarthritis

For PTs & referring clinicians

Coordinate PRP with the rehabilitation plan.

Useful referral information includes symptom behavior, functional goals, rehabilitation dose and response, objective progress, prior procedures, imaging, and the reason an injection is being considered. If PRP is performed, the post-procedure progression should be coordinated with the treating therapist.

UCLA referral information

Common questions

PRP for knee arthritis FAQs

Is PRP proven to regrow knee cartilage?

No. PRP is considered a symptom-modifying treatment. Current evidence does not establish reliable cartilage regeneration, reversal of osteoarthritis, or avoidance of future knee replacement.

Does a 10-billion platelet dose guarantee success?

No. AAPM&R's 2026 guidance identifies at least 10 billion total deliverable platelets as a best-practice target, but the value is not a proven universal threshold and does not predict an individual response.

Is leukocyte-poor or leukocyte-rich PRP better?

For knee osteoarthritis, many protocols favor leukocyte-poor products, but preparation methods and reporting remain inconsistent. Total dose and other cellular characteristics should be considered together rather than relying on one label.

How quickly does PRP work?

When benefit occurs, it is usually assessed over weeks to months rather than immediately. Temporary soreness in the first several days is common. The timing and degree of improvement vary.

Do I need to stop ibuprofen or naproxen?

Your clinician may ask you to avoid NSAIDs around PRP because they inhibit platelet function, but the best timing has not been proven. Do not stop a prescribed NSAID on your own. Follow the individualized instructions for the specific medicine and ask about topical NSAIDs too.

Should I stop aspirin or a blood thinner?

Never stop prescribed aspirin, an antiplatelet medicine, or an anticoagulant without approval from the clinician who prescribed it and the clinician performing PRP. Interruption can create serious cardiovascular or clotting risk.

Which supplements should I report?

Report every vitamin and supplement, especially concentrated garlic, turmeric or curcumin, ginkgo, high-dose vitamin E, and fish oil or omega-3. Evidence is mixed, and a mandatory hold is not established. Do not stop a prescription omega-3 or medically indicated supplement without the prescriber's approval.

What can I take for pain afterward?

Acetaminophen is often the preferred non-anti-inflammatory option when it is medically safe and the clinician performing the procedure approves it. Use only the provided pain plan, especially with liver disease, heavy alcohol use, or combination medicines containing acetaminophen.

When can I exercise after PRP?

Use relative rest for the first 24 hours unless instructed otherwise, then resume motion and loading gradually. There is no single validated knee aftercare program. Follow the indication-specific written plan and coordinate progression with your physical therapist when applicable.

Can I schedule PRP directly?

Call UCLA Orthopedics to arrange an evaluation with Dr. Swisher. Candidacy, product availability, cost, medication instructions, and procedure timing must be reviewed first, so an injection is not guaranteed at the initial visit.

Evidence

Sources and further reading

These sources include supportive and negative evidence so patients and clinicians can see why shared decision-making remains essential.

Evidence and recommendations can change. This page is educational and does not establish whether PRP is appropriate for a particular patient.

PRP injections for knee osteoarthritis: evidence, dose, and recovery.

Written and clinically reviewed by Jeremy Swisher, MD