What Arthrosamid actually is

If your consultant has mentioned Arthrosamid as an option, the first question most patients ask is a practical one: what exactly is it, and how is it different from the steroid or hyaluronic acid injections I've already had?

Arthrosamid is a gel — technically a 2.5% polyacrylamide hydrogel (known as iPAAG), which is 97.5% sterile water. It is neither a drug nor a biologic. Manufactured by Contura International, it is CE-marked and available in the UK as a single 6 mL intra-articular injection administered in an outpatient setting.

What sets it apart is what happens after it enters the knee joint. Rather than temporarily coating cartilage or reducing inflammation for a few weeks, Arthrosamid is designed to physically integrate with the synovial membrane — the tissue that lines the joint capsule — forming a durable, elastic cushioning layer. Unlike corticosteroids, which are absorbed by the body within weeks, or hyaluronic acid viscosupplements, which break down over months, Arthrosamid is not reabsorbed and is intended to remain in place long-term.

It is important to be clear about what this means in practice. Arthrosamid addresses pain and function; it does not modify cartilage, reverse joint damage, or slow the underlying progression of osteoarthritis. The goal is meaningful, sustained symptom relief — not a cure.

The injection procedure

For most patients, the appointment itself is straightforward. Arthrosamid is given as a single intra-articular injection in an outpatient setting — no general anaesthesia, no overnight stay, and no second treatment session. The entire course is complete in one visit.

The injection is delivered under ultrasound guidance, which allows the clinician to confirm precise needle placement within the joint space. Local anaesthesia is applied beforehand, so discomfort during the procedure is typically minimal. Antibiotic prophylaxis is given as standard to reduce the small risk of joint infection.

Before the injection is considered, imaging is obligatory. Plain X-rays establish Kellgren–Lawrence grade and assess the degree of joint space narrowing; MRI provides additional detail on cartilage, the menisci, and the synovial environment. This step is not administrative — it is how the treating clinician confirms appropriate OA grade and rules out contraindications such as inflammatory joint disease or near-complete joint space loss. No injection should be planned without that imaging review in place.

After the procedure, some temporary soreness around the injection site is common; across published studies this has been mild and self-limiting.

What the clinical evidence shows

Five years of follow-up data is rare for any joint injection, and the longest published evidence for Arthrosamid reaches exactly that point. A 2025 prospective extension study tracked 49 participants from a single 6 mL iPAAG injection; of the 27 who completed the full five-year follow-up, statistically significant improvements in WOMAC pain, stiffness, and physical function were sustained throughout — as was Patient Global Assessment, a measure that captures the patient's own sense of how much their condition has changed. In practical terms, improvements at this scale correspond to less pain rising from a chair or climbing stairs, reduced morning stiffness, and greater ability to carry out everyday activities without the knee being a limiting factor. No serious device-related adverse events were recorded across the five-year period.

This durability finding is supported by an earlier systematic review that pooled data from 463 patients and confirmed statistically significant benefit at 52 weeks and 13 months, with one continuation study extending positive results to two years. Arthrosamid was numerically superior to hyaluronic acid in the included RCT — though it is worth being clear that direct head-to-head superiority at long follow-up has not yet been established in a dedicated controlled trial, and research in this area is continuing.

A 2025 retrospective cohort study comparing iPAAG against hyaluronic acid and corticosteroid in 150 patients (Kellgren–Lawrence grade II–IV) reinforced the durability argument: at 12 months, pain scores in both the HA and steroid groups had returned to baseline, while iPAAG WOMAC scores remained stable. The difference between iPAAG and HA at 12 months did not reach statistical significance (p=0.128), so the comparison is better read as a durability signal than a claim of clear superiority across all endpoints.

Who tends to respond best

The profile that emerges most clearly from the evidence is an adult in their fifties or older with Kellgren–Lawrence grade 2 or 3 knee osteoarthritis — meaning visible joint space narrowing but cartilage still present — whose pain has persisted despite a genuine trial of conservative management. In practice, that means physiotherapy and exercise-based rehabilitation, weight management where relevant, a course of oral anti-inflammatories, and at least one round of steroid or hyaluronic acid injections that either failed to provide adequate relief or wore off too quickly.

A 2025 cohort study of 314 knees followed over 24 months identified four independent predictors of achieving a clinically meaningful improvement: older age, lower Kellgren–Lawrence grade, absence of diabetes, and bilateral rather than unilateral knee OA. The same factors that predicted a good response also correlated with a lower likelihood of requiring total knee replacement within two years — suggesting that who is selected and what happens over the longer term are closely connected.

KL grade 4, where joint space is nearly or entirely absent, was the dominant predictor of proceeding to knee replacement despite injection; this is the clinical basis for treating near-complete joint space loss as a contraindication rather than an indication.

Diabetic patients and those with higher OA grades are not automatically excluded, but published evidence suggests their response rates differ from the typical profile above, and counselling on realistic expectations is an appropriate part of the pre-treatment conversation. Patients who are medically unfit for surgery, or who are choosing to defer it for personal reasons, represent a clinically recognised group for Arthrosamid — provided their OA grade falls within the range where meaningful benefit has been demonstrated.

When Arthrosamid is not appropriate

Several situations make Arthrosamid unsuitable, and understanding them helps explain why imaging and specialist assessment are built into the pathway rather than being optional extras.

Severe or bone-on-bone osteoarthritis (KL grade 4) is the most common disqualifying finding. As noted in the preceding section, the hydrogel works by augmenting the synovial membrane; where joint space has been almost entirely lost, there is no meaningful space for it to act within, and knee replacement becomes the more appropriate route.

Active infection — whether in the knee itself or elsewhere systemically — is an absolute contraindication. Injecting any material into an infected joint risks seeding bacteria into a permanent implant, with serious consequences.

Active inflammatory arthritis such as rheumatoid arthritis, gout, or pseudogout means the joint is already driven by a systemic inflammatory process. Introducing Arthrosamid before that is controlled addresses only part of the picture and is unlikely to produce the response seen in standard osteoarthritis.

A prior knee replacement in the same joint and known hypersensitivity to polyacrylamide are straightforward exclusions that imaging review and a standard allergy history will identify.

None of these represent a closed door to treatment overall — they simply redirect towards the most appropriate pathway. A specialist assessment, supported by recent X-ray or MRI, exists precisely to make that determination clearly and individually.

Setting realistic expectations before you decide

The assessment visit is where individual fit is established. Before any injection is planned, imaging — at minimum a recent X-ray, with MRI where the clinical picture warrants it — is reviewed alongside a consultant evaluation to confirm that OA grade, joint space, and general health align with the profile the evidence supports. Patients can self-refer directly without a GP letter; there is no referral barrier to booking that first appointment.

One expectation worth calibrating separately from candidacy: benefit builds gradually over the weeks following injection, not in the days immediately after. Patients who judge the outcome at two or three weeks may be evaluating before the effect has fully settled. Published data tracking suitable patients over several years suggests that, once established, improvement tends to be durable rather than short-lived — but it takes time to arrive.

For a meaningful minority — those at the upper end of OA severity, or with poorly controlled metabolic conditions such as diabetes — the treatment may not deliver a response that crosses the threshold of clinical significance. This is a probability to discuss explicitly at assessment, not something to discover retrospectively. The consultation is also the moment to ask which imaging findings matter most for the decision, what an adequate response looks like in practice, and what the realistic alternatives are if Arthrosamid turns out not to be appropriate.

Lincolnshire Knee, part of the MSK Doctors group, accepts patients without GP referral — assessments can be booked directly at lincolnshireknee.co.uk. The decision about whether Arthrosamid is the right step is made there, in conversation, with the imaging in front of you.

1. [1] Comparative efficacy of polyacrylamide hydrogel versus hyaluronic acid and corticosteroids in knee osteoarthritis: A retrospective cohort study. (2025). https://doi.org/10.1097/MD.0000000000044655 https://doi.org/10.1097/MD.0000000000044655
2. [2] A prospective, open-label clinical investigation of a single intra-articular polyacrylamide hydrogel injection in knee OA: a 5-year extension study. (2025). https://doi.org/10.1186/s13018-025-06526-0 https://doi.org/10.1186/s13018-025-06526-0
3. [3] A Systematic Review of the Novel Compound Arthrosamid Polyacrylamide (PAAG) Hydrogel for Treatment of Knee Osteoarthritis. (2022). https://doi.org/10.18103/mra.v10i8.2950 https://doi.org/10.18103/mra.v10i8.2950
4. [4] Polyacrylamide hydrogel injections in knee osteoarthritis: A PROMs-based 24 month cohort study. (2025). https://doi.org/10.1016/j.jcot.2025.103136 https://doi.org/10.1016/j.jcot.2025.103136