By Dr Fabian Poletti
KNEE osteoarthritis is often described as simple “wear and tear” of cartilage.
In reality, it is a chronic, low- grade inflammatory and degenerative condition affecting the whole joint: cartilage, bone, menisci, ligaments, capsule and, importantly, the synovium — the tissue lining the knee.
When inflamed, the synovium can become painful, swollen and mechanically stiff. Patients with similar X-rays may therefore experience very different symptoms.
Treatment should be based on the patient’s clinical history, physical examination, biomechanics and appropriate imaging — including routine weight-bearing X-rays — rather than on MRI findings alone
What is Arthrosamid?
Arthrosamid is an injectable, non-biodegradable polyacrylamide hydrogel for the symptomatic treatment of adult knee osteoarthritis. It contains 97.5 per cent water and 2.5 per cent cross-linked polyacrylamide.
Unlike temporary injections that are absorbed, it integrates into the synovial tissue and remains there. I describe it as a “liquid implant”. However, a permanent implant does not guarantee permanent pain relief.
It appears to improve the mechanical properties of the synovium and joint capsule, helping to reduce stiffness and potentially modify the local inflammatory environment. However, patients must understand its limitations clearly: it does not regenerate cartilage, correct major deformity or cure osteoarthritis.
Who may benefit?
It may be considered when confirmed knee osteoarthritis continues to cause pain and loss of function despite exercise, physiotherapy, weight management, medication or previous injections.
It can be useful for patients not yet ready for knee replacement, temporarily unsuitable for major surgery, or wishing to postpone surgery after understanding the alternatives.
Patient selection is fundamental. Knee pain may originate from the hip, spine, ligaments, tendons, severe malalignment, inflammatory disease or another condition. An injection cannot correct the wrong diagnosis.
It is less likely to be appropriate with major deformity, instability, mechanical locking, active infection, recent arthroscopy, uncontrolled anticoagulation, an existing knee replacement or end-stage damage clearly requiring surgery.
Studies suggest that approximately seven out of ten carefully selected patients may experience a clinically meaningful improvement.
This also means that around three out of ten may obtain little or no worthwhile benefit. For that reason, no responsible clinician should promise or guarantee a successful outcome.
Benefits have been reported for up to five years after one treatment, but this does not mean every patient will improve for five years.
The longest follow-up involved a small cohort with considerable loss to follow-up. The evidence is encouraging, not absolute.
Ultrasound guidance is essential
Arthrosamid must be administered under ultrasound guidance. This is not an optional extra or a marketing feature.
It must be deposited accurately within the joint, in the correct anatomical location, so that it can interact with the synovial lining as intended. Correct placement is fundamental to safety and to the likelihood of clinical benefit.
Ultrasound allows the surgeon to identify the joint space, visualise the needle continuously, avoid surrounding structures and confirm accurate intra-articular delivery. With a permanent implant, approximate placement is unacceptable.
I perform the procedure in an operating-theatre environment using strict sterile technique. It requires neither general nor spinal anaesthesia, and most patients experience only mild discomfort.
A small amount of local anaesthetic is routinely used, and patients are normally able to return home shortly afterwards.
Temporary pressure, soreness or swelling may occur. Improvement often begins after several weeks and may continue over three to six months.
Why an orthopaedic surgeon is best placed to perform it
Knowing how to insert a needle is not the same as knowing whether a joint should be injected.
An experienced orthopaedic surgeon is best placed to decide because this requires detailed knowledge of joint anatomy, biomechanics, imaging and the progression of osteoarthritis.
The surgeon must distinguish synovial pain from symptoms driven by instability, deformity, meniscal disease, referred pain or end-stage damage.
Crucially, an orthopaedic surgeon knows when an injection is reasonable and when it would merely delay an operation the patient genuinely needs.
Ultrasound improves accuracy, but it cannot rescue poor patient selection. The value lies not only in performing the injection correctly, but in knowing when not to perform it.
Through my UK training and my work with British patients, I became familiar with Arthrosamid when the treatment was already well established and widely known among UK patients with knee osteoarthritis.
I was one of the first orthopaedic surgeons in Spain to introduce it and, to the best of my knowledge, the first in Andalusia, serving patients across the Costa del Sol and Campo de Gibraltar.
My experience has been positive overall, with many patients reporting meaningful improvements. However, a small minority have not responded. Patients deserve to hear both sides.
Can it affect a future knee replacement?
Current evidence does not suggest that the hydrogel compromises a later knee replacement if surgery becomes necessary.
Patients who subsequently underwent knee arthroplasty have not shown operative problems clearly attributable to the injection.
The evidence remains limited, so this is not an absolute guarantee, but treatment does not appear to make future replacement surgery more difficult.
Other joints and imitation products
The authorised indication and strongest evidence concern knee osteoarthritis. Use in the hip, shoulder, ankle or wrist is off-label and should only be considered after specialist assessment, appropriate imaging, discussion of the more limited evidence and explicit informed consent.
“Hydrogel” is a broad category, not proof that products are equivalent. Patients should know the exact device, manufacturer, authorised indication and batch number. A cheaper injectable material is not equivalent merely because someone calls it a hydrogel or “liquid cartilage”.
This is not a cheap or casual injection. Its cost reflects a specialised, traceable medical implant backed by years of research and clinical follow-up, manufactured under medical-device standards and administered under ultrasound guidance and strict sterile conditions.
About Dr Fabian Poletti
Dr Fabian Poletti is a UK fellowship-trained Consultant Orthopaedic and Trauma Surgeon, FRCS (Eng), FEBOT, MSc (Imperial), DIC. He held senior NHS clinical posts and is listed on the GMC Specialist Register.
He later served as Chief Physician in Denmark and has extensive experience across Spanish public and private healthcare. He currently practises in Marbella, Estepona and Gibraltar.
Further information is available at www.drpoletti.com/en.
This article provides general information and does not replace an individual medical assessment.
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