What separates Arthrosamid from hyaluronic acid
Both are non-steroid injections that treat knee osteoarthritis symptoms. Hyaluronic acid is absorbed over months and can be given again, and Sonoscope charges £300 for Ostenil Plus or £350 for Durolane. Arthrosamid is a permanent hydrogel implant at £2,300.
The assumption worth setting aside first: the injection that stays in the knee is not automatically the one that keeps working.
| Feature | Hyaluronic acid (Ostenil Plus or Durolane) | Arthrosamid |
|---|---|---|
| What it is | A sodium hyaluronate gel placed into the knee joint | A non-absorbable polyacrylamide hydrogel implant placed into the knee joint |
| Intended role | Symptom relief and joint lubrication in osteoarthritis | Symptom treatment where non-surgical care has not helped enough |
| Number of injections | One injection with these products, and it can be repeated | One injection, with repeat treatment not studied |
| Permanence | The gel is absorbed and its effect fades | The implant stays in the knee |
| Evidence position | Compared directly with Arthrosamid in one randomised trial. NICE advises against hyaluronan on the NHS | The same trial is the only randomised trial of the product |
| Side effects in that trial | 7.6% of participants reported an effect linked to the treatment | 28.9% of participants reported an effect linked to the treatment |
| Stated clinic fee | £300 Ostenil Plus, £350 Durolane | £2,300 |
Neither injection repairs cartilage or reverses knee osteoarthritis. The two are not given together, and hyaluronic acid must be expected to have been absorbed before Arthrosamid is injected.
What Is In This Article
The head-to-head trial at one year
One randomised trial has compared these two treatments directly, and neither was clearly better. It recruited 239 adults with knee osteoarthritis at three Danish rheumatology sites. Each person received a single 6ml injection of either hyaluronic acid or Arthrosamid, and nobody knew which they had been given.
Pain scores improved in both groups. On the WOMAC pain scale, the hyaluronic acid group improved by 14.8 points and the Arthrosamid group by 18.5. The gap of 3.7 points was small enough to fall inside the margin the researchers had set in advance, and no secondary measure showed a significant difference between the groups either.
That test matters, and it is easy to misread. The trial asked whether Arthrosamid was no worse than hyaluronic acid, not whether it was better. It passed that test. It did not show it was better.
Side effects differed more than the results did. Nine people in the hyaluronic acid group, 7.6% of them, reported an effect linked to the treatment. In the Arthrosamid group, 35 people (28.9%) reported an effect linked to the treatment. All were mild or moderate, and none were serious, but injection-related pain and swelling can carry on for weeks or months.
One detail is worth knowing. The trial used Synvisc-One, which is not one of the two hyaluronic acid products used here. It compares Arthrosamid against hyaluronic acid as a treatment type rather than against Durolane specifically.
5-Year Efficacy Data
The strongest signals for long-term efficacy for Arthrosamid come from two independent 5-year extension studies published in 2025:
- The ROSA RCT Extension (Bliddal et al, 2026): The pivotal randomised controlled trial extension followed patients who initially received Arthrosamid. By year five, the 58 participants who completed the follow-up maintained a clinically meaningful mean reduction of 16.2 points on the WOMAC pain scale (0–100 scale) from baseline.
- The “IDA” Open-Label Study (Bliddal et al., 2025): A separate prospective multicentre cohort in Denmark, originally intended for a 1-year follow-up, was extended to 5 years. The 27 patients who completed the 5-year follow-up demonstrated sustained, highly significant improvements: WOMAC pain decreased by 14.6 points, stiffness by 19.6 points, and physical function improved by 12.5 points.
What NICE says about hyaluronic acid, and what it leaves out
NICE, which sets guidance for the NHS in England, says intra-articular hyaluronan injections should not be offered for osteoarthritis. Its committee pointed to inconsistent benefit across studies. You should know this information before you pay for one.
NHS Commissioning vs. Private Practice
This stance highlights the divide between public health economics and individual patient preference. In an independent, one-stop MSK clinic setting, HA remains a relevant self-pay option. Patients who wish to avoid the potential chondrotoxicity or systemic effects of repeated corticosteroids, or who are seeking a mechanical viscosupplement to bridge a 6-month gap before arthroplasty, often find the benefits of HA clinically meaningful enough to justify the out-of-pocket cost—even if the treatment fails the strict NHS cost-per-QALY thresholds.
Rob Mast’s view is that the research supports a real role for hyaluronic acid and that the deciding factor is patient selection rather than the product. Some people respond very well to it. Others do not. An examination and a scan will help determine which group you fall into.
Arthrosamid is a more novel product and therefore is not as well supported by guidelines. A 2026 review found that the limits in the current evidence prevent routine use of polyacrylamide hydrogel for knee osteoarthritis.
Repeating steroids have limits that hyaluronic acid does not
Steroid injections are not meant to be repeated indefinitely. A two-year randomised trial found greater cartilage volume loss in people given a steroid injection every three months than in those given a dummy injection. Larger observational studies have not found the same effect, so the question is debated rather than settled, and clinicians space steroid injections out either way.
Hyaluronic acid does not carry that concern. It can be repeated without the questions that hang over frequent steroid use, which makes it the more practical option for someone who needs help with the same knee year after year.
Rob has patients who have a hyaluronic acid injection every six to ten months, who report significant improvement and none of the drawbacks they had with steroids. That is not everyone’s experience, and it is not meant to be read as one. It is the reason the assessment comes before the injection rather than after it.
Compare the cost: £300 to £350 against £2,300
Sonoscope charges £300 for an ultrasound-guided Ostenil Plus injection, £350 for Durolane and £2,300 for Arthrosamid. Each fee covers clinical examination, diagnostic ultrasound, the ultrasound-guided procedure, a scan report and aftercare advice.
Durolane is a higher molecular weight product supplied in a larger syringe, and it is the one more often used in bigger joints such as the knee. Ostenil Plus is supplied in a smaller volume. Your examination decides which suits your joint.
The arithmetic is worth doing before you commit. Three Durolane injections spread across three years come to around £1,050, still well below one Arthrosamid injection. If your knee responds to hyaluronic acid, repeating it is the cheaper route, and it leaves the permanent option available later.
Several things shape the decision:
- Your current function. Pain at rest, difficulty walking and limits on daily activity all point towards different treatment priorities.
- This means you can keep the option open. Hyaluronic acid can be repeated. Arthrosamid is a one-way decision.
- What you have already tried. Previous injections and how your knee responded matter more than any headline claim.
- How you feel about a permanent implant. Arthrosamid cannot be removed once it is given.
- Your budget. The gap between the two is large, and it is a fair thing to weigh rather than an awkward one.
If a previous injection gave little benefit, that prompts a fresh assessment rather than an automatic step up to the more expensive option.
Rehabilitation is what makes either injection worth having
Symptom relief is worth most when it helps you move more easily and get back to rehabilitation. Strengthening or aerobic exercise suited to you remains the core of knee osteoarthritis care, with weight management alongside it where appropriate.
Your pain, stiffness and physical function describe the problem more usefully than imaging alone. A real-time ultrasound scan assesses the knee alongside the clinical examination.
Rob Mast carries out your assessment and diagnostic ultrasound, so the person judging whether an injection is appropriate is the person who examined the knee. Where the findings support it, examination, scan and treatment can happen in one visit.
An injection chosen after examination and real-time ultrasound has a defined purpose behind it: helping you move, exercise and protect your function. An injection chosen based on a price tag or a duration claim does not have a defined purpose.
Common questions about knee arthritis injections
Can Arthrosamid and hyaluronic acid be given together?
No. They are separate treatments. Hyaluronic acid must be expected to have been absorbed before Arthrosamid is injected, so the two are spaced apart rather than combined.
Can I have hyaluronic acid again if it wears off?
Yes, and that is one of its practical advantages. There are recognised concerns about repeating steroid injections too often, which is why they are spaced out. Hyaluronic acid does not carry the same questions, and some people have it every six to ten months over a period of years.
Who tends to do well with hyaluronic acid?
There is no single answer, which is why selection matters. Your symptoms, physical function, previous knee responses, and examination and scan results all feed into it. Some people get excellent results and others get little, and an honest assessment is the only way to judge which is likely.
Do I need a GP referral before a private knee injection assessment?
No. You can see your GP for advice or arrange a private consultation directly. You also do not need a scan, X-ray or MRI beforehand unless your symptoms suggest one is needed.
Does either injection repair damaged knee cartilage?
No. Both treat symptoms such as pain and stiffness. Current evidence does not show that either one regrows cartilage or reverses knee osteoarthritis.
Is Arthrosamid worth around seven times the price?
That depends on what you want from it. In the only trial comparing them, Arthrosamid did not produce significantly better pain, stiffness or function than hyaluronic acid at 12 months. What it offers instead is a single permanent treatment, and whether that is worth the difference is a judgement your assessment can inform.
Does severe knee arthritis automatically rule out either injection?
No. Symptoms and physical function guide treatment more usefully than imaging severity on its own, and your assessment establishes whether either injection has a sensible role.
This is general information, not medical advice.
Reviewed by Rob Mast, Advanced Practice Physiotherapist and Sonographer, Honorary Lecturer in Musculoskeletal Diagnostic Ultrasound at Brunel University.
References:
Bliddal, H., Hartkopp, A., Beier, J., Conaghan, P.G. and Henriksen, M., 2025. A prospective, open-label, clinical investigation of a single intra-articular polyacrylamide hydrogel injection in participants with knee osteoarthritis: a 5-year extension study. Journal of orthopaedic surgery and research, 21(1), p.43.
Bliddal, H., Beier, J., Hartkopp, A., Conaghan, G.C. and Henriksen, M., 2026. Sustained symptom relief and safety over five years following a single intra-articular injection of 2.5 [%] polyacrylamide hydrogel in patients with knee osteoarthritis. Clin. Exp. Rheumatol.
Henriksen, M., Beier, J., Hartkopp, A., Conaghan, P.G. and Bliddal, H., 2023. 3 year results from a prospective study of polyacrylamide hydrogel for knee osteoarthritis. Osteoarthritis and Cartilage, 31(5), pp.682-683.