Arthrosamid® — a single-injection treatment for knee osteoarthritis
A new generation of treatment for osteoarthritis pain: a single ultrasound-guided injection designed for long-lasting relief — in Lisbon and Almada.
Dr Miguel Reis e Silva
Medical Director of Sport Lisboa e Benfica
Medical Director and Founder of the Myalgia Clinics
What is Arthrosamid?
Arthrosamid® is an injectable hydrogel made of 97.5% water and 2.5% polyacrylamide — a biocompatible, non-degradable material that has been used in medicine for decades.
Unlike hyaluronic acid, which the body gradually reabsorbs, Arthrosamid® is not absorbed: after intra-articular injection, the hydrogel integrates into the synovial membrane of the knee, helping to improve the joint environment, cushion the joint and reduce osteoarthritis pain.
The treatment consists of a single injection, performed at Clínica Myalgia® under real-time ultrasound guidance.
When is it indicated?
Arthrosamid® may be an option to consider if:
You have knee osteoarthritis with pain that limits daily life, walking or sport;
You have had limited or short-lived benefit from hyaluronic acid, PRP or corticosteroid injections;
You are looking for a longer-lasting solution, without repeating injections every few months;
You want to delay or avoid knee replacement surgery, or you are not a candidate for surgery;
You want to stay active while controlling your osteoarthritis symptoms.
The decision is always individual: at the assessment we look at your knee, the degree of osteoarthritis and the treatments you've already had, and we explain openly whether Arthrosamid® is the best option for you — or whether another approach would make more sense.
Why have Arthrosamid at Clínica Myalgia?
100% ultrasound-guided injection — correct placement of the hydrogel in the joint space is essential; ultrasound ensures it with millimetre precision;
Strict clinical criteria — we only suggest Arthrosamid® when it is properly indicated; it isn't the answer for every knee or every degree of osteoarthritis;
A full assessment of the cause — at Myalgia, the injection is part of a plan that may include movement analysis, biomechanical correction, physiotherapy and custom insoles, to protect the knee in the long term;
Elite sport experience — the same high standards we apply to elite athletes, for every person;
Two locations — Lisbon (Carnide) and Almada.
How does the procedure work?
Medical assessment — medical history, physical examination, ultrasound and review of imaging (X-ray or MRI). We confirm the indication and answer all your questions.
Preparation — thorough disinfection and local anaesthetic. If there is a joint effusion, it is drained before the injection. A single dose of antibiotic is usually given as prophylaxis, in line with the manufacturer's recommendations.
Ultrasound-guided injection — the hydrogel is injected into the knee joint space under continuous ultrasound visualisation. The procedure is quick and usually well tolerated.
Recovery — most people return to their usual activities within a few days, with specific guidance for the first week.
Follow-up — review of your progress and, when indicated, integration with physiotherapy and therapeutic exercise to maximise knee function.
Arthrosamid, PRP or Hyaluronic acid?
All three options have a place in treating knee osteoarthritis, with different profiles: hyaluronic acid acts on lubrication and inflammation, with an effect lasting several months that can be repeated; PRP aims to stimulate the body's own repair mechanisms; Arthrosamid® stands out for being a single injection aimed at a longer-lasting effect. At the assessment we compare the options for your specific case — including costs, expectations and the available evidence.
Frequently asked questions
How long does the effect of Arthrosamid® last?
Arthrosamid® was developed for a long-lasting effect after a single injection, since the hydrogel is not reabsorbed by the body. Published studies show sustained pain relief over several years in many patients, although the response varies from person to person and with the degree of osteoarthritis.
Is the improvement immediate?
No. The effect builds up gradually over the first few weeks after the injection, as the hydrogel integrates into the synovial membrane. It is normal not to feel much difference in the first few days.
Does the procedure hurt?
It is usually well tolerated. We use local anaesthetic, and ultrasound guidance makes the technique more precise and comfortable. There may be mild discomfort or a feeling of "fullness" in the knee for the first few days, which settles on its own.
When can I return to normal activity and sport?
Most people return to daily activities within a few days. The return to sport is gradual and guided at consultation, depending on your knee and your sport.
Is Arthrosamid® safe?
Polyacrylamide hydrogel is biocompatible and has a well-studied safety profile. As with any injection, there is a small risk of local reaction or infection — minimised by sterile technique, ultrasound guidance and antibiotic prophylaxis. All safety questions are reviewed with you at the consultation.
Can I have Arthrosamid® if I've already had hyaluronic acid or PRP?
Yes — in fact, a significant proportion of people who choose Arthrosamid® do so precisely because they had limited or short-lived benefit from other injections. The appropriate interval after previous treatments is set at the consultation.
Can the treatment be repeated?
As a rule, Arthrosamid® is intended as a single injection. In selected cases, an additional injection may be considered — a decision made at clinical review.
What if the osteoarthritis is very advanced?
In very advanced osteoarthritis, the response to any injection tends to be more limited, and surgery may be the most appropriate option. We'll be open with you: if Arthrosamid® isn't a good option for your knee, we'll tell you — and help you find the right path.