Reviewed August 2026 · Dr Yas Edirisinghe MBBS FRACS FAOrthA · Hip & Knee Surgeon, Adelaide
If your knee or hip hurts, someone has probably suggested an injection. Some injections genuinely help — for a while. Others cost hundreds of dollars and do nothing. This guide explains honestly which is which, based on the best research available, so you and your GP can decide together. One rule before we start: an injection can calm a joint, but no injection can repair one.
What are gel injections (hyaluronic acid)?
Hyaluronic acid — sold as Synvisc-One, Durolane, Monovisc or Euflexxa — is a gel similar to natural joint fluid, injected into the knee. Patients usually call these “gel injections.”
They are slow. If a gel injection is going to help, relief builds over about 4 to 8 weeks — not days. They last longer. When they work, benefit can last up to 6 months. And it’s honest to say they don’t work for everyone: international guidelines no longer recommend them routinely, because across all patients the average benefit is small. But averages hide the pattern that matters for you.
When a gel injection may be worth trying: mild to moderate arthritis, in a knee that still has cartilage, in someone who isn’t ready for surgery — especially if cortisone helped but wore off too fast.
When it is not worth trying: bone-on-bone arthritis. Gel cannot help a joint that has run out of cartilage. And if one properly placed gel injection gave you nothing, repeating it won’t either.
How do gel injections compare with cortisone?
Cortisone is a strong anti-inflammatory. It works quickly — usually within days — and wears off after roughly 4 to 12 weeks. It suits a painful flare, or getting comfortable for something that matters. The catch: research shows repeated cortisone injections may actually speed up cartilage wear, which is why no surgeon recommends cortisone as a long-term plan. Gel is the mirror image: slower to start, longer to last, for the right knee.
What about PRP and stem cells?
PRP (platelet-rich plasma) is heavily marketed, but in the most rigorous trial to date — 288 patients, published in JAMA — PRP was no better than salt-water injections for pain or cartilage at 12 months. Stem-cell injections remain unproven for arthritic joints and often cost $5,000 or more. Our advice on both is simple: save your money outside a registered clinical trial.
What do knee injections cost in Adelaide?
Here’s the part few people are told: a cortisone injection, guided by ultrasound or CT, is often bulk billed when your GP refers you to an Adelaide radiology practice. Hyaluronic acid isn’t covered by Medicare or the PBS — expect roughly $300–$700 privately. PRP has no rebate at $300–$800 per injection.
The 3-month rule every patient should know
If there is any chance you’ll have a joint replacement soon: no cortisone into that joint within 3 months of surgery. Injections shortly before a replacement roughly double the risk of deep infection in the new joint. Always tell your surgeon about every injection you’ve had, and when.
When is an injection the wrong answer?
Injections stop earning their keep when pain wakes you at night despite them, your X-ray shows bone-on-bone, each injection helps less than the last, or the joint locks or gives way. That’s the moment to talk through your options properly — which is a conversation, not a commitment to surgery.
Not sure where your knee stands? Take our free 2-minute knee self-check — you’ll get your score and a plan matched to your result, instantly. Wondering about the bigger picture? Read Do I need a knee replacement?
GPs: our detailed prescribing-level guide with the evidence tables is in the GP Hub injections guide.
This article is general information, not a diagnosis. Decisions about injections should be made with your GP or specialist. Dr Yas sees privately referred patients usually within two weeks, considers non-surgical options first, and will tell you exactly where you stand. Call 08 7081 4100.