Injections occupy an awkward space in knee arthritis. They are widely offered, widely marketed, and the evidence behind them varies from reasonable to absent depending on which one you are being offered. This page separates them.
One thing to be clear about first: no injection reverses arthritis. Nothing currently available regrows articular cartilage in an arthritic knee. Anyone telling you otherwise is selling something. What injections can do is buy time, treat a flare, and occasionally help work out where the pain is coming from.
Corticosteroid.
The most useful of them, and the cheapest. A corticosteroid injection into the joint reduces inflammation and, in most people, reduces pain for somewhere between a few weeks and a few months. It works best when the knee is actively inflamed: swollen, warm, in a flare.
Its honest limitations. The effect is temporary and tends to shorten with repetition. Repeated injections into the same joint are not harmless, and most practices space them at no more than three or four a year. There is some evidence that frequent, repeated intra-articular steroid is associated with cartilage loss, which matters more in a younger knee than in an older one.
It is also useful diagnostically. If a steroid injection into the knee joint produces no change at all, that is genuine information: it suggests the pain may not be coming from inside the joint.
Timing rule. An intra-articular steroid injection within roughly three months before a knee replacement is associated in the published literature with a higher rate of subsequent infection. If a replacement is on the horizon, say so before you have the injection, because the sequence matters.
Hyaluronic acid.
Marketed as viscosupplementation, the idea being to restore the lubricating properties of joint fluid. It is heavily advertised and it is expensive.
The evidence is genuinely mixed. Meta-analyses have reached different conclusions depending on which trials they include and how they handle the placebo response, which in knee injection trials is large. Several international guidelines now advise against routine use in knee osteoarthritis; others describe a small effect in some patients. What can be said fairly is that any benefit is modest, it is not structural, and it does not justify the cost for most people.
If you have had it and it helped you, that is worth knowing and there is no reason to stop on principle. It is not something this practice will push you towards.
PRP and stem cell injections.
This is where the marketing outruns the evidence by the widest margin, and where people spend the most money.
Platelet-rich plasma involves spinning down your own blood and injecting the platelet fraction. Trials exist, some are positive, many are small, unblinded or industry linked, and the preparations differ so much between clinics that results do not transfer. There is no good evidence that PRP alters the structure of an arthritic knee.
"Stem cell" injections in the knee are usually bone marrow aspirate concentrate or adipose-derived cells. In Australia these are regulated and the claims made for them are frequently outside what the evidence supports. The AOA and the TGA have both taken positions on the marketing of unproven cell-based therapies for osteoarthritis. As with PRP, no structural benefit has been demonstrated.
The practical advice is not that these are dangerous. It is that they are expensive, unproven for structural benefit, and often sold to people at exactly the point where a straightforward conversation about the alternatives would serve them better. If you are considering one, ask what specific outcome is being promised, over what timeframe, and what the published evidence for that specific preparation is.
The other procedures that come up.
Arthroscopy for arthritis. Not supported. Multiple randomised trials have shown no benefit from arthroscopic washout or debridement for knee osteoarthritis over placebo or conservative care. Professor Rodda does not perform knee arthroscopy, and that page explains the position in full.
Genicular nerve radiofrequency ablation. Burning the small sensory nerves that carry pain signals from the knee. There is reasonable evidence for medium-term pain relief, and it has a genuine role for people who are not candidates for surgery or who want to defer it. It is performed by pain specialists and interventional radiologists rather than here; see radiofrequency ablation.
Braces and unloader braces. An unloader brace can help genuine single-compartment arthritis by shifting load off the worn side. They are cumbersome and compliance is the limiting factor, but for the right knee they are a legitimate option and they cost less than most injections.
Where injections fit.
They sit alongside, not instead of, the things with the strongest evidence base, which are strengthening, load management and weight where relevant. An injection that buys you three comfortable months is most valuable if those are three months you spend building the quadriceps rather than three months you spend resting.
Nothing here is a reason to delay a decision indefinitely. If the knee is at the point where injections are all that keeps it tolerable, that in itself is part of the answer to is it time for a knee replacement.
References.
- Australian Orthopaedic Association National Joint Replacement Registry. Hip, Knee & Shoulder Arthroplasty Annual Report. Adelaide: AOA.
- Bedson J, Croft PR. The discordance between clinical and radiographic knee osteoarthritis: a systematic search and summary of the literature. BMC Musculoskelet Disord. 2008;9:116.
Common questions.
How many cortisone injections can I have in my knee?
Most practices space them at no more than three or four a year in the same joint. The effect tends to shorten with repetition, and there is some evidence that frequent repeated intra-articular steroid is associated with cartilage loss, which matters more in a younger knee.
Should I have a cortisone injection if surgery is being considered?
Tell the rooms first. An intra-articular steroid injection within roughly three months before a knee replacement is associated in the published literature with a higher rate of subsequent infection, so the sequence and the timing matter.
Do stem cell or PRP injections work for knee arthritis?
There is no good evidence that either alters the structure of an arthritic knee. Trials are mixed, often small, and preparations differ so much between clinics that results do not transfer. They are not offered here.
Does hyaluronic acid injection help?
The evidence is mixed. Any benefit is modest and not structural, and several international guidelines now advise against routine use in knee osteoarthritis. If you have had it and it helped, there is no reason to stop on principle.
Is an arthroscopy worth trying before a knee replacement?
Not for arthritis. Multiple randomised trials have shown no benefit from arthroscopic washout or debridement for knee osteoarthritis over placebo or conservative care. Professor Rodda does not perform knee arthroscopy.
This page provides general information about a medical condition and a surgical procedure. It is not individual medical advice and does not replace consultation with a qualified practitioner. Outcomes vary between individuals and all surgery carries risk. A referral is needed for a consultation with Professor Daevyd Rodda; without one, you can start with the practice nurse practitioner, who can provide it.