For appropriately selected adults with knee osteoarthritis, current evidence suggests that hydrogel injections have a generally favourable safety profile. However, they are not risk-free or suitable for everyone. Understanding possible side effects, contraindications and the limits of current research can help you make a more informed decision.

What does the safety evidence show?

When discussing hydrogel injections for knee osteoarthritis, treatment commonly refers to Arthrosamid, a non-absorbable polyacrylamide hydrogel. It contains 97.5% water and 2.5% cross-linked polyacrylamide and is injected directly into the knee joint.

Clinical studies have produced reassuring safety findings so far. A three-year follow-up from a randomised controlled trial followed people who had received one polyacrylamide hydrogel injection. Between years one and three, researchers recorded 50 adverse events among 36 participants, but none were considered related to the hydrogel treatment.

A separate five-year study also reported a favourable safety profile. During its extension period, researchers recorded 47 adverse events but no serious events attributed to the device and no new adverse device effects. However, only 27 of the original 49 participants completed the five-year follow-up, so the results should be interpreted alongside that limitation.

A 2026 review of available research found that transient pain was the most commonly reported adverse event, occurring in approximately 16% of patients across the evidence reviewed. No serious complications were reported in the included studies, although the authors said limitations in study quality and long-term evidence mean the treatment should still be used cautiously.

What side effects can occur?

Like other injections into a joint, hydrogel injections can cause temporary discomfort around the treated knee. Pain or soreness after treatment appears to be the most frequently reported issue in current research.

Patients should also understand that any procedure involving an injection carries potential risks. The manufacturer provides specific instructions about where and how Arthrosamid must be injected, including warnings against injecting it into blood vessels, outside the joint or directly into the synovial tissue or capsule.

Because Arthrosamid is non-absorbable, it differs from injections designed to gradually disappear from the body. This makes correct placement, sterile technique and appropriate patient selection particularly important.

You should receive a clear explanation of expected symptoms after treatment and instructions about when to contact your clinic. Significant or worsening pain, unusual swelling or signs suggesting infection should always be medically assessed rather than assumed to be part of normal recovery.

Who should not have hydrogel treatment?

Not every patient with knee pain is suitable for hydrogel injections. Arthrosamid's manufacturer states that it should not be injected when there is an active skin disease or infection at or near the injection site or when the knee joint is infected or severely inflamed.

Treatment is also contraindicated for people with haemophilia or uncontrolled anticoagulant treatment because of the associated bleeding risk. The manufacturer provides additional warnings and precautions that the treating clinician should review as part of the pre-treatment assessment.

This is why a consultation matters. Your clinician should review your diagnosis, general health, medications, previous knee procedures and any existing infections before recommending treatment.

Hydrogel treatment should also not be viewed as a general injection for every painful joint. Current clinical use of Arthrosamid focuses specifically on symptomatic knee osteoarthritis, so other causes of knee pain may require completely different treatment.

How certain are we about long-term safety?

The available studies are encouraging, but the evidence is still developing. Three- and five-year follow-up studies have reported favourable safety findings, providing more information about longer-term use than was previously available.

However, a 2026 review concluded that limitations in study quality, understanding of the treatment mechanism and long-term evidence currently prevent researchers from recommending routine use without caution.

NICE has also considered Arthrosamid for health technology guidance but did not select it because the evidence available for its evaluation process was considered insufficient. This does not mean the treatment has been shown to be unsafe; rather, it highlights that further robust evidence is still needed.

So, are hydrogel injections safe? Current studies suggest that polyacrylamide hydrogel can be used with a favourable safety profile in appropriately selected adults with knee osteoarthritis, with temporary pain being the most commonly reported adverse event. However, treatment has contraindications, long-term evidence is still growing and no medical procedure is completely risk-free.

If you are considering hydrogel treatment for persistent knee osteoarthritis, contact The Regenesis Clinics for an individual assessment. A specialist can review your medical history, explain the potential benefits and risks, and determine whether hydrogel treatment is appropriate for you.