Arthrosamid® Knee Injection
A long-lasting injection for knee osteoarthritis — without surgery
What is Arthrosamid®?
If you have knee arthritis and your painkillers, physiotherapy or steroid injections are no longer giving you the relief they used to — but you’re not ready for, or not suitable for, a knee replacement — Arthrosamid® may be an option worth discussing with me. It’s a newer type of injection for knee osteoarthritis, and I now offer it at the Winterbourne hospital, Dorset.
Arthrosamid® is a hydrogel — a soft, water-based gel (2.5% polyacrylamide, 97.5% water) — that is injected into the knee in a single treatment. Unlike a steroid injection, which settles inflammation for a few weeks or months, or hyaluronic acid, which the body absorbs over time, Arthrosamid® isn’t broken down and absorbed. Instead it becomes integrated into the lining of your knee joint, where it acts as a long-lasting cushion. It’s a simple, one-step procedure performed under local anaesthetic, and you’re in and out of the clinic the same day.
Arthrosamid® — a single-injection hydrogel treatment for knee osteoarthritis (image: Contura).
Arthrosamid® integrating with the synovial tissue in the knee (image: Contura).
How does Arthrosamid® work?
When I inject Arthrosamid® into the synovial cavity of your knee, the gel settles into and combines with the synovium — the soft tissue lining of the joint. Over roughly 6 to 12 weeks it becomes integrated into that lining, softening it and improving its elasticity. This cushioning effect is what reduces the pain of osteoarthritis, and because the gel stays in place rather than being absorbed, that relief can last far longer than a traditional injection — from a single treatment.
Understanding knee osteoarthritis
In a healthy knee, smooth cartilage cushions the joint and the synovial lining produces fluid that lubricates movement. In osteoarthritis, the cartilage wears away, the synovial tissue becomes inflamed (synovitis), and bone begins to rub on bone — causing the pain, stiffness and swelling you feel. Arthrosamid® works on that inflamed synovial lining, which is why it can help even though it doesn’t regrow cartilage.
A healthy knee compared with a knee affected by osteoarthritis and synovitis (image: Contura).
What happens during the procedure?
The treatment is straightforward and takes place in clinic:
- First, I clean the skin around your knee and give you a local anaesthetic to numb the area. You’ll also be given antibiotics beforehand to protect against infection.
- I then inject the Arthrosamid® in a single step into the synovial cavity of your knee. I may use ultrasound guidance to make sure it’s placed accurately.
- The needle is removed and a small plaster is placed over the injection site. That’s it — most patients leave the clinic shortly afterwards.
Arthrosamid® is given as a single injection under local anaesthetic (image: Contura).
What should I expect afterwards?
Many patients feel little discomfort, but as the anaesthetic wears off your knee may feel sore, and you might notice some mild swelling at the injection site for a few days. You can continue your normal medication and painkillers as usual. Because the gel is more viscous than other injections, the knee can feel a little different afterwards — that’s normal. As with any injection into a joint, I’d recommend avoiding strenuous activity such as tennis, jogging or long walks for the first few weeks, and easing back into things gradually.
When will I feel the benefit? Some patients notice relief within 24 hours, but it typically takes four to twelve weeks to feel the full effect as the gel integrates into the joint lining. This is a gradual improvement rather than an instant fix.
Is Arthrosamid® proven? The evidence
I think it’s important to be balanced about this. Arthrosamid® is a newer treatment, and I’ll always give you my honest view on whether it’s right for you. That said, the clinical evidence behind it is genuinely encouraging, and the safety profile of the underlying hydrogel is now supported by many years of data. Here’s what the studies show.
Response rates by age (ROSA study)
In the ROSA study, patients under 70 reported close to an 80% positive response rate following treatment, based on improvement in WOMAC pain scores. Response was measured as the proportion of patients who improved, stayed the same, or declined.
Responder rates by age, ROSA study (chart: Contura/Arthrosamid). N=107 all patients; N=44 over-70s; N=63 under-70s.
Reproducible results across multiple studies
The benefit isn’t a one-off finding. Consistent improvements in pain and function have been reproduced across several independent studies — including the IDA, ROSA, LUNA and DAISY studies — giving greater confidence in how the treatment performs.
Reproducible results across the IDA, ROSA, LUNA and DAISY studies (chart: Contura/Arthrosamid).
Long-term safety
The polyacrylamide hydrogel used in Arthrosamid® has a safety profile established over many years of use in the body for various indications, and the treatment is documented to remain safe and effective for its intended use five years after a single injection. This long-term safety record is one of the reasons I’m comfortable offering it as an option.
Reproducible results across the IDA, ROSA, LUNA and DAISY studies (chart: Contura/Arthrosamid).
Frequently Asked Questions
Am I suitable for Arthrosamid®?
Arthrosamid® tends to work best for people with mild to moderate knee osteoarthritis whose symptoms limit their daily life, particularly if steroid injections have helped but not lasted, or if you want to delay a knee replacement. It’s generally not the right choice for very advanced, bone-on-bone arthritis, where a knee replacement usually gives a better result. The only way to know for sure is an assessment — I’ll examine your knee, review your X-rays, and give you my honest recommendation, which may or may not be Arthrosamid®.
How is it different from a steroid or hyaluronic acid injection?
A steroid injection calms inflammation but typically only lasts weeks to a few months. Hyaluronic acid aims to lubricate the joint but is gradually absorbed by the body, and the evidence for it is mixed. Arthrosamid® is different because it isn’t absorbed — it integrates into the joint lining and stays there, which is why a single injection can provide much longer-lasting relief.
How long does it last?
Clinical trials have shown that the benefit can be sustained to two years, and the treatment remains safe and effective five years after a single injection. As it’s a newer treatment, we don’t yet have decade-long effectiveness data, and I’ll always be straight with you about that.
Is it a cure for my arthritis?
No — and I think it’s important to be honest about that. There is no cure for osteoarthritis. Arthrosamid® can reduce or relieve your knee pain, but it doesn’t regrow cartilage or reverse the arthritis, and in some cases arthritis may still progress.
Can I have both knees treated?
Yes, it’s possible to have both knees treated with Arthrosamid®. If both your knees are affected, I’ll advise on the best timing and sequence for your treatments.
Can I have the treatment again if it wears off?
Yes. Although formal trials on repeat treatment are limited, further Arthrosamid® treatments are not contraindicated and can be discussed. If the benefit fades over time, we can talk about a repeat injection.
Will it affect a future knee replacement?
On the current evidence there’s no indication that having Arthrosamid® prevents or complicates a knee replacement later. Importantly, if you do go on to have any major surgical or dental procedure in the future, you should tell the treating team that you have an Arthrosamid® implant in your knee so they have an accurate picture.
Are there any side effects?
Clinical trials reported no serious side effects. The most common effects were joint pain and a sensation of joint swelling, usually mild and lasting days to a few weeks. If your knee becomes red, hot, very swollen or increasingly painful after treatment, you should contact me straight away.
Should I have physiotherapy afterwards?
Structured rehabilitation can help you get the most from the treatment, and I’ll discuss a plan that suits you. As with my joint replacement patients, I’m a firm believer that the stronger the muscles around your knee, the better your knee functions.
Is Arthrosamid® right for you?
If knee arthritis is limiting your life and you’d like to explore whether Arthrosamid® could help, I’d be glad to see you. You can book a consultation in person, by telephone, or by video call at The Winterbourne Hospital, Dorchester, or Harbour Hospital, Poole.
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