PRP and 'stem cell' injections for knee arthritis — what the evidence says

Platelet-rich plasma (PRP) and so-called “stem cell” injections are heavily marketed as regenerative treatments for knee arthritis. Patients understandably ask whether they work. An honest, evidence-based answer matters here, because these treatments are often expensive, not covered by Medicare, and the marketing frequently outpaces the science.

What they are

PRP is made by taking a sample of the patient's own blood, concentrating the platelets, and injecting that concentrate into the joint. The idea is that growth factors in platelets may reduce inflammation and support tissue health.

“Stem cell” injections usually involve cells harvested from the patient's own fat or bone marrow. It is important to know that, despite the name, these preparations are not purified stem cells and do not regrow cartilage. The term is widely used in marketing in a way that overstates what is being delivered.

What the evidence shows

For PRP, some studies suggest it may reduce pain in mild to moderate knee arthritis, at least for a period, and it appears reasonably safe because it uses the patient's own blood. However, the quality of the evidence is mixed, preparations are not standardised, and major guidelines do not currently endorse it as a routine treatment.

For “stem cell” therapies, the evidence is weaker still. There is no good evidence that they regenerate cartilage or reverse arthritis. Professional bodies have repeatedly cautioned patients about unproven cell-based treatments marketed for arthritis.

Neither PRP nor 'stem cell' injections regrow cartilage or cure arthritis. The realistic question is whether they reduce symptoms for a time.

Cost and regulation

These treatments are generally not covered by Medicare or private health funds and can be costly. Patients should be cautious of clinics that promise cartilage regeneration or a cure, as these claims are not supported by evidence and are not consistent with regulatory guidance.

How PRP compares with other injections

PRP is best understood alongside the two other commonly offered knee injections. Cortisone (corticosteroid) injections have the strongest track record for short-term relief of an inflamed joint, but the effect is temporary and repeated injections are used cautiously. Hyaluronic acid (“gel”) injections aim to improve joint lubrication; the evidence for meaningful benefit is mixed, and major guidelines do not strongly endorse them. PRP sits in a similar territory — possibly helpful for symptoms in milder arthritis, clearly not disease-modifying. None of the three alters the underlying arthritis, and none is a substitute for the better-evidenced foundations of weight management, strengthening exercise and activity modification.

Red flags when assessing a clinic

Because this area is commercially driven, patients should be alert to warning signs. Be cautious of clinics that promise cartilage regeneration or “avoiding a knee replacement”, quote large upfront fees for a course of injections, rely on patient testimonials rather than published evidence, or recommend treatment without an up-to-date X-ray or a proper clinical assessment. A trustworthy clinician will explain the limits of the evidence, present the alternatives, and be comfortable with you seeking a second opinion before spending money.

Where these injections fit in a sensible treatment pathway

For most patients with knee arthritis, the pathway begins with the treatments that consistently work: weight reduction where relevant, a structured strengthening programme guided by a physiotherapist, simple analgesia used wisely, and activity modification. Cortisone has a role for settling a flared joint. PRP may be reasonable for selected patients with milder disease who understand its limits and costs. When arthritis is advanced and quality of life is significantly affected despite these measures, joint replacement remains the treatment with the strongest and longest evidence of benefit — and delaying it with repeated unproven injections can mean years of avoidable pain.

What the major guidelines say

Patients do not need to take any individual clinic's word for it — the position of the major professional bodies is publicly available. The Royal Australian College of General Practitioners' guideline on knee osteoarthritis recommends against stem cell therapy and does not support PRP as a routine treatment, citing the limited and inconsistent evidence. International orthopaedic and rheumatology bodies have taken similar positions, and Australian regulators have acted repeatedly against clinics making unproven regenerative claims. Guidelines evolve as better trials are published, and PRP in particular remains an active research area — but at present, no major guideline recommends either treatment as established care for knee arthritis. That gap between the marketing and the guidance is the single most useful fact for a patient weighing up an expensive course of injections.

A sensible position

PRP may be a reasonable option for some patients with milder arthritis who wish to try a low-risk injection before considering surgery, provided they understand the evidence is limited and the cost is their own. Claims of regeneration should be treated sceptically. For established, severe arthritis, no injection substitutes for the proven benefit of joint replacement when the time is right.

The bottom line

The best-evidenced non-surgical treatments for knee arthritis remain weight management, exercise and physiotherapy, with a clear role for surgery once these are exhausted. PRP and cell-based injections are an area of genuine interest, but the marketing is well ahead of the science — so approach them with informed, realistic expectations.