Platelet-rich plasma (PRP) has become one of the most discussed treatments in orthopaedics over the past decade. Clinics offering PRP injections have proliferated — and so has the marketing language surrounding them. Terms like "regenerative therapy" and "stem cell activation" are used loosely, often implying more than the evidence supports.

The reality is more measured: PRP does produce meaningful pain relief and functional improvement in a proportion of patients with knee osteoarthritis — but the benefit is temporary, not all PRP preparations are equal, and PRP does not reverse structural joint damage. Understanding these distinctions helps patients make an informed decision about whether PRP fits into their treatment plan.

What Is PRP?

Blood contains red cells, white cells, platelets, and plasma. Platelets are small cell fragments whose primary role in healing is to release growth factors — proteins that regulate inflammation, stimulate tissue repair, and attract stem cells to an injury site.

PRP is made by drawing a small volume of the patient's own blood (typically 15–60ml), spinning it in a centrifuge to concentrate the platelets, and injecting the resulting plasma into the affected joint. The platelet concentration in PRP is approximately 3–8 times higher than in whole blood, delivering a concentrated dose of growth factors directly into the arthritic environment.

The Evidence: What Works and What Doesn't

Where evidence supports PRP

Mild to moderate knee OA (Kellgren-Lawrence Grade 1–3) · Pain relief at 3–6 months · Functional improvement sustained to 12 months with high-platelet PRP · Superior to hyaluronic acid injections in multiple meta-analyses

Where evidence is less convincing

Severe OA (Grade 4, bone-on-bone) · Long-term structural benefit (no evidence PRP slows progression) · Low-platelet PRP preparations · Single injection vs. series of 2–3 injections

Based on articles retrieved from PubMed, a meta-analysis by Bensa et al. (2025, American Journal of Sports Medicine) analyzed 18 randomized controlled trials involving 1,995 patients. PRP provided statistically and clinically significant improvements in both VAS pain scores and WOMAC function scores compared to placebo at 3 and 6 months. Crucially, the analysis revealed that platelet concentration matters: high-platelet PRP (over 1,000,000 platelets/μL) produced clinically meaningful pain relief at 3, 6, and 12 months, while low-platelet PRP failed to reach the minimum clinically important difference for pain. DOI: 10.1177/03635465241246524

However, a large, high-quality RCT — the RESTORE trial by Bennell et al. (2021, JAMA), involving 288 patients with mild to moderate knee OA — found no significant difference between PRP and saline placebo in pain scores or cartilage volume at 12 months. This trial used a leukocyte-poor PRP preparation. DOI: 10.1001/jama.2021.19415

What this tells us: Not all PRP is the same. The concentration of platelets, the presence or absence of leukocytes, and the number of injections likely all influence outcomes. The preparation method matters as much as the decision to use PRP at all.

What PRP Can and Cannot Do

PRP can

  • Reduce pain and improve function in mild to moderate knee OA for 3–12 months
  • Modulate the inflammatory environment in the joint
  • Provide an alternative to repeated steroid injections (which may harm cartilage with frequent use)
  • Supplement or bridge treatment while awaiting surgery, or as part of a non-surgical management strategy

PRP cannot

  • Regrow cartilage or reverse structural joint damage
  • Reliably help advanced (bone-on-bone) arthritis
  • Replace appropriate surgery when surgery is indicated
  • Guarantee a response — approximately 30–40% of patients do not respond meaningfully

Who Is a Good Candidate for PRP?

PRP is most appropriate when

  • Mild to moderate knee OA (Kellgren-Lawrence Grade 1–3) on X-ray
  • Significant symptoms despite physiotherapy and activity modification
  • Patient wants to avoid or delay surgery
  • Patient has not responded adequately to hyaluronic acid injections
  • Contraindication to steroid injections (e.g. poorly controlled diabetes)

PRP as Part of a Broader Treatment Plan

In my practice, PRP is not offered as a standalone miracle solution — it is one component of a broader strategy that should include structured physiotherapy, weight management where relevant, and a clear plan for what happens if non-surgical treatment fails to provide adequate relief.

For patients who are ultimately heading toward surgery — whether HTO, UKA, or TKA — PRP injections can help manage symptoms in the interim and may improve the biological environment for post-surgical healing in some contexts.

Frequently Asked Questions

How many injections do I need?

Most protocols use 2–3 injections spaced 2–4 weeks apart. A single injection may provide some benefit but is generally less effective than a series. The protocol is adapted based on the patient's response to the first injection.

How long does PRP last?

Clinical benefit typically peaks at 3–6 months and, in patients who respond well, may persist to 12 months. Some patients benefit from repeat injections after 6–12 months. PRP does not provide permanent relief — it manages symptoms rather than addressing the underlying structural problem.

Is PRP better than hyaluronic acid (viscosupplementation)?

The evidence generally favors PRP over hyaluronic acid for knee OA in terms of pain relief and function. Multiple meta-analyses show PRP to be superior, particularly at 3–6 months follow-up.

My MRI shows bone-on-bone arthritis. Will PRP help?

In advanced arthritis with significant bone loss, PRP is unlikely to provide meaningful or sustained benefit. At that stage, the joint environment is too far degraded for growth factors to produce meaningful tissue response, and surgical options — UKA, TKA, or HTO in appropriate candidates — are likely more appropriate.

Is PRP covered by Japanese national health insurance?

Currently, PRP injection for knee osteoarthritis is not covered under Japan's standard NHI and is offered as a self-pay procedure. The cost varies by facility and preparation method. I provide a clear written estimate before any procedure.

Knee arthritis — not sure what to do next?

First consultation is free — 30 minutes, in person or by video. I will review your imaging and give you an honest, evidence-based recommendation.

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References

Bensa A, et al. PRP Injections for the Treatment of Knee Osteoarthritis: The Improvement Is Clinically Significant and Influenced by Platelet Concentration. Am J Sports Med. 2025;53(3):745–754. DOI: 10.1177/03635465241246524

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. DOI: 10.1001/jama.2021.19415