Platelet-rich plasma for the knee

How it works

Platelets carry growth factors that the body normally releases at the site of an injury. Concentrating them and delivering them into an osteoarthritic joint is intended to shift the balance in the joint away from inflammation and towards repair signalling.

It is not a lubricant and it does not replace joint fluid. The mechanism is biological rather than mechanical, which is also why it takes longer to show an effect than either steroid or hyaluronic acid.

What the session involves

Blood is drawn from your arm, usually 15 to 60 ml. It is spun in a centrifuge for around ten minutes to separate the platelet-rich layer. That layer is drawn off and injected into the knee, often under ultrasound guidance. The whole appointment runs about an hour.

The honest position on the evidence

PRP has reasonable support in younger patients with early osteoarthritis and weaker support in advanced disease. The difficulty in reading the literature is that PRP is not one product: platelet concentration, the presence or absence of white cells, and whether the preparation is activated all vary between systems, and studies rarely report them in a way that allows comparison.

When a clinic quotes a success rate, ask which system they use and what platelet concentration it achieves. A clinic that cannot answer that is quoting somebody else's results.

Side effects

• Aching and swelling in the knee for one to three days, common and expected.
• Bruising at the blood draw site.
• Infection, rare, as with any joint injection.
• No allergy risk from the material itself, since it comes from your own blood.

Who it suits

Active patients under about 60 with mild to moderate osteoarthritis who want to keep running or playing sport, who have tried and outgrown simpler options, and who accept both the cost and the fact that results are less predictable than with a standardised injection.

If the priority is the longest possible interval between clinic visits for the lowest predictable cost, a cross-linked hyaluronic acid with collagen tripeptide does that job more cheaply in a single visit.