Private Arthrosamid® Injections for Knee Osteoarthritis

Arthrosamid® is a genuine step beyond traditional knee injections. Rather than temporarily lubricating or calming the joint, it becomes part of the joint lining, creating a lasting cushioning scaffold that supports your knee every time you move.

What is Arthrosamid®?

Arthrosamid® is a 2.5% injectable polyacrylamide hydrogel (iPAAG), a non-biodegradable, water-rich gel that integrates with the knee's synovial lining to reduce stiffness and pain. It's supplied as six pre-filled 1 ml syringes (6 ml total). Unlike treatments that need frequent repetition, this single injection provides long-lasting relief by creating a permanent scaffold within your knee joint.

I've been performing ultrasound-guided knee injections for over 10 years, including thousands of procedures through my NHS consultant-level role. What sets Arthrosamid apart is its mechanism: rather than simply lubricating the joint like a hyaluronic acid injection, it becomes part of the joint lining. In recent peer-reviewed research, its pain relief has been maintained for up to five years after a single injection (Bliddal et al., 2026).

Understanding knee osteoarthritis

Osteoarthritis is a degenerative condition affecting cartilage, the smooth, cushioning layer between your bones. Think of cartilage like the space between a door and its frame: when that space narrows, the door creaks and sticks. As cartilage thins, the bones underneath get closer together, creating stress and inflammation that leads to pain and restricted movement (though not everyone with cartilage loss has pain).

Several factors contribute: age-related changes (not inevitable), repetitive activities, previous injuries, being overweight (fat cells also produce inflammatory chemicals that damage cartilage), and genetics. While age and genetics can't be changed, much can be addressed through exercise, weight management and targeted treatments like Arthrosamid.

Arthrosamid is one option among several. For the full picture of how it compares with exercise, weight management, corticosteroid, hyaluronic acid and PRP, see my complete guide to knee osteoarthritis treatment.

How does Arthrosamid® work?

When I inject Arthrosamid into your knee, it doesn't provide immediate relief like a steroid. Instead, over the following months it integrates with your joint capsule, the 'bag' surrounding your knee. This creates a permanent cushion-like scaffold that stabilises the joint and limits compression when you walk or move.

Think of it as scaffolding around a building: the gel merges with your joint capsule, preventing it from folding and compressing excessively during movement, which reduces pain and improves function. Hydrogels like Arthrosamid have a long safety record, the same technology has been used in urogynaecology for many years. Relief often starts in weeks, builds over 1–3 months, and has been maintained in studies through at least three years, with five-year data now peer-reviewed and ten-year data presented more recently (Bliddal et al., 2026).

When you'll feel the difference

Are you a good candidate?

Clinical studies and expert consensus point to three main criteria that define who is most likely to benefit. These are general guides rather than a personal decision, the final judgement is always made with a clinician at your assessment.

Primary eligibility criteria

1. A meaningful level of pain. In the main studies (including the Keele University trial), people had significant knee pain, generally more than 40 out of 100 on a pain scale (the Visual Analogue Scale, or VAS).
2. Mild-to-moderate osteoarthritis on X-ray. Kellgren–Lawrence grade 2 to 3. Arthrosamid is generally not recommended for severe, "bone-on-bone" arthritis (grade 4).
3. Persistent symptoms despite conservative care. Ongoing pain, aching or stiffness on most days of the past month, despite measures such as physiotherapy, oral pain relief or previous short-acting injections.

Other factors that improve the odds

• Under 70, manufacturer-reported success drops from close to 80% to about 62% after age 70
• A healthy weight, outcomes are less predictable when BMI is over 30
• No acute joint inflammation
• Previous imaging (X-ray or MRI) to confirm the diagnosis

I particularly recommend Arthrosamid for active people who want a long-term solution rather than repeated treatments, and those trying to delay or avoid knee surgery. Studies show sustained improvement for at least three years, with newer data suggesting five years or longer.

How does it compare to other injections?

A recent head-to-head study showed Arthrosamid was at least as effective as hyaluronic acid at 52 weeks (Bliddal et al., 2022). The key difference is that Arthrosamid integrates permanently into the joint lining, so structural support lasts for years rather than months, it isn't just masking symptoms temporarily.

There's also a practical difference in what a course of treatment actually involves. PRP, for example, is usually given as a series of two to three injections spaced a few weeks apart, whereas Arthrosamid works from a single injection. Please note that I don't currently offer PRP at Insight MSK; for knee osteoarthritis I provide corticosteroid, hyaluronic acid and Arthrosamid injections, all under ultrasound guidance.

Why ultrasound guidance is essential

This is crucial: Arthrosamid must be placed precisely within the joint capsule. Studies show even experienced clinicians have a 10–25% chance of missing the joint when injecting without ultrasound. With steroids, missing the target isn't catastrophic, the medication is absorbed. But Arthrosamid doesn't dissolve. If injected outside the joint it remains there permanently and could form a granuloma requiring surgical removal. Ultrasound guidance provides absolute certainty of correct placement, and having performed thousands of knee injections, you can be confident yours will be placed accurately.

What are the risks?

• Allergic reactions, extremely rare, and more likely from the local anaesthetic than the gel. I monitor all patients and carry emergency medication and training.
• Infection, the main concern with any joint injection, particularly with a non-biodegradable substance. I prescribe prophylactic antibiotics per manufacturer guidance (typically azithromycin and flucloxacillin, or clindamycin for penicillin allergy) to take 1–2 hours before the procedure.
• Post-procedure pain or swelling is the most common side effect, and more frequent than many people expect. In the pivotal randomised trial, mild-to-moderate injection-related effects, mostly temporary joint pain or swelling, were reported by about 29% of Arthrosamid patients, compared with about 8% after hyaluronic acid; all settled without lasting problems and none were serious (Bliddal et al., 2024). A long-acting local anaesthetic helps, but it's sensible to expect the knee may be sore or stiff for a few days, and occasionally a couple of weeks, while the gel settles.

Overall, Arthrosamid has a good long-term safety record, with no evidence of later reaction or joint damage in studies out to five years. It does, though, carry a higher rate of short-term post-injection soreness than hyaluronic acid, so it's worth planning the timing for when you can take things a little easy for a few days afterwards.

The treatment process

First, we have a telephone consultation (15–30 minutes) to review your symptoms, previous treatments and imaging. You'll need recent imaging (X-ray or MRI) beforehand, mainly to exclude other conditions. On the day, I perform an ultrasound examination to check for acute inflammation (severe synovitis is a contraindication) or a large fluid build-up (which can be drained first), then deliver the six syringes of Arthrosamid through a single needle entry, all under ultrasound guidance.

Clinical evidence & success rates

Arthrosamid's effectiveness isn't just anecdotal. Studies show patients maintain statistically significant pain reduction for three years after a single injection, with over 62% meeting the OMERACT-OARSI criteria for meaningful improvement at one year. In the landmark IDA study, 49 participants received a single 6 ml injection (46 completed 52-week follow-up), showing a significant WOMAC pain reduction of 17.7 points, well above the minimum clinically important difference.

• Patients under 70: nearly 80% success (manufacturer-reported)
• Patients over 70: around 62% success

Success is measured with the WOMAC score (Western Ontario and McMaster Universities Osteoarthritis Index), a 24-item questionnaire covering pain, stiffness and physical function. I ask all my Arthrosamid patients to complete it before treatment, giving us a baseline to track genuine, measurable improvement.

A patient story

Frequently asked questions

References