Most people who ask us about Arthrosamid have already been through the standard route: painkillers, physiotherapy, a steroid injection or two. Some get a few weeks of relief before things slide back. Others get very little from any of it. By the time they reach us, they’re wondering what’s left before surgery becomes the only conversation on the table.
Arthrosamid is one answer to that question. For the right patient, it can be a significant one.
What is Arthrosamid?
Arthrosamid is an injectable hydrogel made from 97.5% sterile water and 2.5% cross-linked polyacrylamide. It’s injected directly into the knee joint, where it integrates with the synovial fluid — the lubricating fluid that naturally surrounds the joint.
What sets it apart from other knee injections is that it doesn’t break down. Steroids are metabolised by the body within weeks. Hyaluronic acid — used in products like Ostenil, Durolane, and Sinovial — lasts three to six months before the body absorbs it. Arthrosamid is non-biodegradable, which means once it’s injected, it remains in the joint as a permanent part of the environment.
The way to think about it: a knee affected by osteoarthritis has lost some of its natural cushioning. The cartilage that once absorbed impact has thinned or worn unevenly. The synovial fluid has changed in quality. Arthrosamid doesn’t repair cartilage — no injection does — but it adds a flexible, gel-like layer within the joint that absorbs load, reduces friction, and restores some of what the joint has lost.
How does the Arthrosamid injection work?
After injection, the hydrogel disperses through the synovial fluid as you move your knee. Over the following four to six weeks, it becomes integrated with that fluid. Over three months, it gradually incorporates into the synovial membrane — the joint lining itself.
This is why we always tell patients not to judge the result too early. The injection isn’t like a steroid, which can take effect within days. Arthrosamid works progressively. Most patients notice a meaningful improvement at around four weeks, with the peak benefit typically appearing between eight and twelve weeks. After that, the effect stabilises.
Because Arthrosamid is non-biodegradable, the mechanical cushioning it provides doesn’t fade the way a biological substance would. The hydrogel doesn’t wear out or get reabsorbed. This is the basis for the long-term benefit data — which we’ll come to shortly.
Who is Arthrosamid suitable for?
Arthrosamid is designed for people with knee osteoarthritis — specifically, mild to moderate osteoarthritis — who are still in significant pain despite conventional treatments.
The typical patient we see is someone who has tried physiotherapy and found it wasn’t enough on its own. Someone whose steroid injections worked initially but stopped giving adequate relief, or stopped lasting as long. Someone who isn’t at the stage where surgery is being recommended, or who would rather exhaust non-surgical options first.
Clinically, the assessment involves confirming the diagnosis — ideally with X-ray or MRI — and establishing the degree of joint change. Arthrosamid works best where there’s still meaningful joint space remaining. In very advanced osteoarthritis, where the joint surfaces are essentially bone on bone, the hydrogel has less to work with and results tend to be less predictable.
Who is not suitable for Arthrosamid?
Not everyone with knee pain is a candidate, and it’s worth being clear about that rather than raising expectations that won’t be met.
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Inflammatory arthritis — Rheumatoid arthritis, psoriatic arthritis, and similar conditions involve a different disease mechanism to osteoarthritis. Arthrosamid is not designed for these and won’t address the underlying inflammatory process.
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Active infection — Any active infection in or near the knee rules out any injection procedure until it’s resolved.
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Anticoagulant medication or bleeding disorders — If you’re on blood thinners or have haemophilia, this needs careful assessment before any injection is considered.
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Recent knee surgery — If you’ve had a knee replacement or arthroscopy in the past six months, Arthrosamid is not appropriate at this stage.
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Ligament instability — If pain is being driven by mechanical instability — for example, a significant untreated ACL injury — a hydrogel injection addresses the wrong problem. Structural instability needs a structural solution.
If you’re unsure whether you’re suitable, a consultation is the right first step. We’d rather tell you honestly that Arthrosamid isn’t the right fit than administer something that isn’t going to help.
What does the evidence say?
The clinical evidence for Arthrosamid has developed substantially over the past few years, with some of the longest follow-up data now available in this area.
The largest study to date is the LUNA study — a multicentre observational study with almost 200 participants. It found that a single injection produced statistically significant reductions in pain, with WOMAC pain scores (a standard measure in osteoarthritis research) improving by an average of 17 points. Crucially, those improvements held at the one-year mark.
Four-year data presented at the European Orthopaedic Research Society meeting in 2024 showed that a single dose maintained statistically significant pain reduction at that time point. The following year, five-year efficacy data and ten-year safety data were both presented at the World Congress on Osteoarthritis — among the longest-running datasets in the field. No significant adverse events were recorded across that decade.
A 2025 comparative study looked at 150 patients treated between 2023 and 2024 with either Arthrosamid, hyaluronic acid, or corticosteroid injections. Arthrosamid outperformed steroids at six months and showed comparable results to hyaluronic acid at that point, while providing substantially longer duration of effect than either.
The honest summary: the evidence supports Arthrosamid as a meaningful option for the right patient. It is not a cure, and it doesn’t regenerate cartilage. But it can provide real, lasting pain relief — from a single procedure — for patients who haven’t found adequate relief from other injections.
How does Arthrosamid compare to other knee injections?
Steroid injections act by reducing inflammation in the joint. They work quickly — often within a few days — which makes them a good choice for acute flare-ups or when someone needs fast relief. The limitation is duration: the effect typically fades within six to twelve weeks, and repeated steroid injections carry risk of tissue damage over time.
Hyaluronic acid injections (Ostenil, Durolane, Sinovial and others) supplement the joint’s natural lubricating fluid. They take a couple of weeks to reach full effect and generally last three to six months — a step up from steroids in terms of duration, and without the tissue risk of repeated steroid use.
Arthrosamid sits above both in duration of effect. Clinical data supports meaningful benefit lasting two to five years from a single injection. The trade-off is cost — significantly higher than either alternative — and the slower onset of effect. For patients who have been on a cycle of repeat injections every few months, the cost-per-year comparison often changes the picture considerably.
How much does Arthrosamid cost in the UK?
Arthrosamid is not available on the NHS. It is a private procedure.
Across UK clinics, pricing typically ranges from around £1,500 to £2,500 per knee, with London and South East clinics generally at the higher end of that range. At Physio & More in Kingston, all Arthrosamid injections are performed by Dr Robert Henderson under real-time ultrasound guidance. If you’d like to discuss pricing or find out whether you’re suitable, contact us to arrange a consultation.
What happens on the day of the injection?
You’ll have a brief pre-procedure consultation to confirm your suitability and go through the consent process. Dr Henderson uses ultrasound imaging to locate the optimal injection point in real time — the needle position is visible on screen throughout. Local anaesthetic is applied first, so the injection itself is generally well tolerated. The whole procedure takes around 15 to 30 minutes.
Most patients walk out of the clinic without assistance. You should avoid strenuous activity or heavy impact on the knee for the first 48 hours, but day-to-day activities are fine immediately. Driving home is usually fine.
Some patients notice mild swelling or achiness in the knee for a few days post-injection. This is a normal response and settles on its own. The gradual improvement in pain typically begins at around four weeks and continues building through the three-month mark.
Frequently asked questions about Arthrosamid
Does the Arthrosamid injection hurt? The injection site is numbed with local anaesthetic first, so most patients find the procedure manageable. There may be mild pressure during the injection, and the knee can feel sore for a few days afterwards. Serious pain during or after the procedure is uncommon.
How quickly does Arthrosamid work? Most patients notice a meaningful change at around four weeks. The full effect develops over three months as the hydrogel integrates fully with the joint.
Can both knees be treated at the same time? Yes. If both knees are affected, both can be injected in the same appointment.
How long does Arthrosamid last? Clinical data supports meaningful benefit lasting two to five years from a single injection. A 10-year safety study presented in 2025 showed no significant adverse effects across that period.
Does it work if I’ve already had steroid injections? Yes. Previous steroid injections don’t rule out Arthrosamid. Most patients who come to us for Arthrosamid have already had one or more steroid injections that have stopped working or lost effectiveness over time.
Can I have Arthrosamid again if the effect wears off? The evidence on repeat injections is still developing. In clinical practice, a second injection has been given in some cases where the first provided good relief but eventually faded. This would be assessed on a case-by-case basis.
Is Arthrosamid suitable for all stages of knee osteoarthritis? No. It works best in mild to moderate osteoarthritis where meaningful joint space remains. Very advanced disease with severe bone-on-bone changes tends to respond less predictably.
If you’d like to find out whether Arthrosamid is the right option for your knee, book a consultation with Dr Robert Henderson at Physio & More in Kingston upon Thames.