Two injectables, two different jobs

Both names come up during the same research session, both are injected into the knee, and neither involves surgery — so the question most patients arrive with is a reasonable one: how do I know which one I need?

The short answer is that they target different parts of the joint and serve different clinical goals. ChondroFiller is an injectable collagen scaffold. Once placed inside the knee under ultrasound guidance, it gels in situ across the articular surface and provides a structural matrix that recruits the patient's own progenitor cells — a process called acellular matrix-induced chondrogenesis. Its job is to address the cartilage surface itself: the worn, load-bearing tissue on the ends of the bones.

Arthrosamid works on a different layer entirely. It is a permanent polyacrylamide hydrogel that integrates with the synovial membrane — the soft tissue lining the joint cavity. Rather than rebuilding the articular surface, it acts through mechanical viscosupplementation at the synovial lining and appears to reduce the inflammation that membrane generates, which is strongly associated with OA pain levels. A single injection is designed to provide sustained relief rather than structural repair.

Neither product is a generic filler, and their mechanisms should not be collapsed into one category. Some patients with a joint that is both worn on the surface and reactive in the lining may be suited to both — a combination approach covered later in this article.

Both are delivered as ultrasound-guided outpatient injections, with no theatre admission or general anaesthetic required. Neither is currently funded by the NHS, and both are accessed on a self-funded private basis.

The patient ChondroFiller is designed for

Cartilage surface loss is the primary indicator — diffuse wear across the joint compartment, a focal area of damage, or a combination of both. KL Grade III/IV osteoarthritis is the most common presentation at consultation, but the treatment is not confined to a particular grade or age group. There is no upper age ceiling, and because the collagen scaffold creates its own surface effect from the point of placement, it does not depend on the joint being young or the defect being small.

The regenerative aim is what distinguishes ChondroFiller from the palliative or symptom-control options: the goal is to support structural repair of the articular surface, not simply to reduce pain through a different mechanism. Patients whose symptoms are primarily mechanical — worse on loading, related to joint surface loss — rather than dominated by synovitis and rest pain are the clearest candidates.

Bone-on-bone status does not automatically exclude a patient. Where other cartilage procedures rely substantially on host tissue regenerating across a well-defined lesion, this scaffold pathway provides cushioning cover from injection. The clinical threshold is therefore less dependent on residual cartilage health than is sometimes assumed.

In clinical evaluations, IKDC scores in knee patients have improved by approximately 30 points over 12 months — a consistent signal across multiple studies, though individual outcomes vary and should be discussed at consultation rather than treated as a fixed prediction.

ChondroFiller is applicable across multiple joints — hip, shoulder, ankle, and smaller joints — though the comparison in this article remains focused on the knee.

The patient Arthrosamid is designed for

Rest pain is the clearest early signal. Patients who describe aching at night, swelling that returns without obvious cause, or inflammatory flares that do not track neatly with physical activity are presenting the symptom picture that points toward Arthrosamid rather than a surface scaffold. In knee osteoarthritis, the synovial membrane — the tissue lining the joint cavity — tends to become chronically inflamed, and that inflammation appears to be strongly linked with pain severity independent of cartilage loss.

Arthrosamid addresses that layer directly. A single 6 mL injection of the polyacrylamide hydrogel integrates with the synovial lining after placement, acting as a viscosupplement at that level and appearing to reduce the inflammatory activity of the lining tissue. The hydrogel is permanent — it does not resorb — and the relief it provides can be sustained rather than time-limited. Published data suggest a single injection may reduce symptoms for up to three years.

The clinical evidence includes a 12-month open-label study by Bliddal et al. (J Orthop Surg Res, 2024) confirming both effectiveness and safety. Separately, a 2022 study by Maulana, Cole, and Lee documented a reduction in bone marrow lesions following a single injection in patients with advanced knee OA — a finding that adds to the picture of the product's reach, though it requires further investigation.

Two things warrant stating plainly. Arthrosamid does not repair or regenerate articular cartilage — its mechanism operates at the synovial lining, not the cartilage surface — so patients expecting structural tissue restoration would be better served by a different pathway. And the permanence of the hydrogel is a fact to weigh at the outset, not discover afterwards.

For patients who are not surgical candidates, or who wish to delay knee replacement while managing symptoms effectively, Arthrosamid offers a sustained-relief option delivered in a single outpatient injection. Suitability is assessed individually at consultation, considering joint match, OA stage, symptom profile, and expectations — a framework informed by outcomes from more than 600 treated patients.

When the joint needs both at once

Some knees present with both problems at once — articular surface loss combined with active synovial inflammation — and neither product alone addresses both tissue layers. The CFI+ combination exists for exactly that scenario: ChondroFiller is delivered as the regenerative scaffold, targeting the cartilage surface, while Arthrosamid lines and calms the synovial membrane. Both are placed during a single outpatient appointment, from £5,500.

The mechanism distinction is essential here and must not be collapsed. ChondroFiller provides a collagen matrix that recruits the body's own cells to support structural repair at the joint surface — the regenerative component. Arthrosamid, the permanent polyacrylamide hydrogel, acts at the synovial lining — the anti-inflammatory, viscosupplement component. The two products are not interchangeable versions of the same intervention; the combination is additive because each acts on a different tissue through a different route.

Whether the combination fits a given patient requires careful clinical assessment. Anatomy must suit both injections, the OA stage must be appropriate, the symptom pattern needs to show both surface-related and inflammatory drivers, and the patient's goals must align with what the combination can realistically achieve. Not everyone with surface loss and synovitis will meet all of those criteria. The self-funded cost is also higher than either injection alone — a practical factor to discuss before committing. Suitability is determined at consultation, informed at London Cartilage Clinic by outcomes across more than 600 treated patients.

What the evidence actually shows

Knowing that a treatment works and understanding how well it has been tested are two different questions — and in a self-funded decision, the second one matters.

For ChondroFiller, the picture beyond functional scores includes MOCART cartilage-imaging scores in the range of 70–87 and a complaint rate of approximately 0.06% across published series. The evidence base draws primarily on manufacturer-supported clinical evaluations alongside smaller independent studies; this is not unusual for a CE-marked Class III device at this stage of wider adoption, but it does mean independent replication is still developing.

For Arthrosamid, the key published findings — the Bliddal open-label study and the Maulana and Lee bone marrow lesion data described in the previous section — represent short-to-medium term follow-up. In practical terms, the most comprehensive controlled data currently extends to 12 months. Because the hydrogel is permanent in the joint, questions about decade-long intra-articular behaviour remain open; longer registries are still accumulating. The safety literature is broadly favourable over that window, but this is a relevant factor when weighing a permanent implant at any age.

Neither product has been compared directly against the other in a randomised controlled trial. No head-to-head RCT exists, which means any comparison between them rests on separate evidence streams rather than controlled trial data — a limitation worth holding in mind when reading reviews, including this one.

Both are self-funded. Neither is available on the NHS, and at the time of writing neither Bupa nor AXA covers them through standard private medical insurance policies.

Getting the right assessment

The decision between these two injectables — or the question of whether to combine them — cannot be resolved without a proper clinical assessment. Imaging findings, symptom profile, joint stage, and functional goals all shape the pathway, and they pull in different directions depending on the individual joint.

MSK Doctors consultants see knee cartilage cases at Sleaford in Lincolnshire, where an Open MRI scanner is available on site, and at the Grantham centre. Neither appointment requires a GP referral, and there is no NHS-style waiting list.

You can book a consultant-led assessment at mskdoctors.com without a referral.

For a self-funded treatment — and particularly one that may involve a permanent implant — that initial consultation is not a formality. It is where the evidence, the imaging, and the patient's own priorities are brought together. The right answer for a given knee may be one product, the other, both, or neither; that determination is only reliably reachable through a structured clinical assessment rather than a comparison article.