Arthrosamid: one injection, measured in years

What it is

Arthrosamid is an injectable hydrogel, two and a half per cent cross-linked polyacrylamide and the rest sterile water. It is given as a single 6ml injection into the knee. It is not a drug and it is not a steroid.

What makes it different is that it does not break down. Other injections are absorbed by the body over weeks or months, which is why their effect fades and why they get repeated. Arthrosamid integrates into the synovial lining of the joint capsule and stays there, cushioning the joint and settling the inflammation that drives the pain.

What the research shows

The LUNA study is the largest to date. At one year, WOMAC pain scores had improved by an average of 17 points, with similar gains in stiffness and physical function. No serious treatment-related adverse events were seen. These results are reported by the manufacturer and have not yet appeared as a peer-reviewed publication, so we label them as such rather than dress them up.

The Danish IDA study followed 49 people after a single injection and found improvements in pain, stiffness and function sustained at three years, with follow-up continuing toward five. A separate randomised trial of 239 adults has been followed to three years, with pain scores still 13 points below baseline at that point.

Roughly one in four people do not get a meaningful improvement. We would rather you heard that now than found it out in three months.

Who it tends to suit

Knees with arthritis confirmed on imaging, typically Kellgren-Lawrence grade two or three. People who have not had lasting relief from physiotherapy, anti-inflammatories or exercise alone. People whose previous injections helped but not for long. Knees that swell. Anyone wanting to delay a knee replacement, or who is not a candidate for surgery.

It is less likely to help an end-stage knee with very little joint space left. It is not a treatment for rheumatoid or other inflammatory arthritis. We cannot tell you which of those you are from an email. That is what the scan is for.

When you would feel a difference

This is not an instant treatment, and expecting it to be is the most common cause of disappointment. Some people respond by around four weeks. Most fall between four and twelve. Some take anywhere from twelve weeks to six months. Please do not judge it at week three.

In our experience the patients who do best are the ones who commit to the strengthening work afterwards. A stronger quadriceps and hip takes load off the joint surface every time you stand, walk or climb a stair. The injection is what makes that work possible. It is not a substitute for doing it.