What most patients want to know first

For most patients researching this treatment, the first question is simple: how long will it actually last, and will they need the injection again?

ChondroFiller™ is an injectable collagen scaffold placed under ultrasound guidance — not a lubricant, drug, or filler that the body metabolises and that then needs topping up. Its durability rests on biology: the scaffold works by acellular matrix-induced chondrogenesis, meaning it recruits the patient's own progenitor cells into the collagen matrix, where they progressively build endogenous repair tissue. Because the benefit comes from that newly formed tissue rather than from the scaffold itself — which resorbs as repair takes hold — the mechanism is fundamentally different from an injection that simply wears off.

In practical terms, published follow-up data run to three years with maintained outcomes in patients with focal cartilage defects; company-reported and linked sources describe sustained results at five years and beyond in suitable candidates. For the right patient, the realistic expectation is a single treatment session rather than an ongoing repeat-injection schedule.

How that compares with Arthrosamid®, hyaluronic acid, and corticosteroid — and what the clinical evidence actually shows — is set out in the sections that follow.

The clinical evidence at 3 and 5 years

The strongest independent dataset comes from the prospective post-market clinical follow-up (PMCF) study by Jerosch et al., which tracked patients with focal knee cartilage defects beyond 12 months. At three years, mean IKDC scores reached 80 — a mean improvement of 32.4 points from baseline, marginally higher than the one-year figure and well above the established minimal clinically important difference (MCID) of 16.7 points. MOCART MRI scores followed a complementary trajectory, rising from 65.3 at four weeks to 81.6 at one year and holding steady across published studies (range 81.6–84.3) — indicating sustained structural repair on imaging rather than early fill followed by deterioration.

Independent corroboration at shorter horizons adds weight to this picture. A 2016 randomised controlled study against microfracture confirmed IKDC improvement maintained at one year, with progressive cartilage maturation on imaging. At a smaller scale, a 2024 study from University Hospital Pleven, Bulgaria — 17 patients followed across 2012–2023 — reported statistically significant improvements in IKDC and Lysholm scores at 3, 6, and 12 months, with results plateauing between 6 and 12 months, suggesting functional benefit consolidates within the first year.

Five-year data exist but carry a caveat worth naming plainly: published cohorts citing maintained IKDC and MOCART outcomes at that horizon draw primarily on company-reported and echo-linked sources rather than independent RCTs extended to five years. The three-year Jerosch follow-up currently represents the strongest peer-reviewed durability anchor.

On safety, the reoperation rate in published ChondroFiller™ cohorts stands at 3–8%, compared with up to 41% for microfracture and 37% for ACI/MACI procedures.

Why the mechanism is the durability story

Think of the collagen scaffold as temporary construction hoarding around a repair site. Its job is not to be the final structure — it is to hold the space and signal to the body that work should begin.

When ChondroFiller™ gel is placed under ultrasound guidance into a focal cartilage defect, the collagen matrix attracts progenitor cells from the surrounding synovium and subchondral bone — a process called acellular matrix-induced chondrogenesis. Those cells migrate in, differentiate, and begin laying down new tissue. A 2025 ex vivo study quantified this directly: DNA content within the scaffold rose 2.4-fold by day 14, confirming that cell recruitment occurs early and as intended. Laboratory models do not automatically translate to clinical outcomes, but the finding gives direct mechanistic support to what the longer-term clinical data already suggest.

As cells progressively fill the defect, the collagen scaffold itself resorbs — typically over one to two years post-injection. What remains is the patient's own repair tissue. There is no pharmacological agent to clear and no filler to degrade over time, which is why durability here is a structural question rather than a chemical one: once repair tissue is established at the defect site, the biological rationale for loss of effect disappears.

This mechanism is tied to a specific patient profile — those with focal, contained defects rather than diffuse joint degeneration. The matching criteria are discussed in the patient-selection section that follows.

Arthrosamid® durability: what the 5-year data show

Arthrosamid® works through an entirely different principle from the collagen scaffold described above. The 2.5% polyacrylamide hydrogel is non-biodegradable: injected into the sub-synovial tissue, it integrates permanently into the joint lining and acts as a mechanical cushion rather than a biological repair agent. It does not promote tissue regeneration and is not designed for focal defects; its licensed indication is diffuse knee osteoarthritis (Kellgren–Lawrence grade II–IV).

The durability evidence for Arthrosamid® now rests on two five-year prospective datasets. A pre-registered RCT extension (NCT04045431) followed 58 completers and demonstrated a sustained WOMAC pain improvement of −16.2 points at year five (95% CI −20.0 to −12.4; p<0.0001), with no device-attributed adverse events recorded during the extension phase. A separate prospective open-label study — 49 participants enrolled, 27 completing the full five years — confirmed significant improvements across all WOMAC domains (pain −14.6, stiffness −19.6, physical function −12.5) and patient global assessment (−13.4), maintained throughout the observation window. Both studies reported a clean safety profile over the period. The design caveat worth noting is that neither dataset is double-blinded beyond year one: the longer-term arms are observational extensions, which limits the strength of inference compared with a parallel-controlled trial carried to five years.

Shorter-horizon evidence adds breadth. The 2022 Cole et al. systematic review pooled 463 patients and confirmed statistical significance at 52 weeks, 13 months, and two years. A 2025 retrospective cohort study (150 patients, 50 per group) found that VAS pain scores in both the hyaluronic acid and corticosteroid groups had returned to baseline by 12 months, while the Arthrosamid group remained stable — though the 12-month difference did not reach statistical significance.

In clinical practice, Arthrosamid benefit is typically characterised as lasting two to three years on average, with a meaningful proportion of patients maintaining improvement to five years on the current evidence.

Where HA and corticosteroid sit on the durability scale

Hyaluronic acid (HA) and corticosteroid are the most widely used injection options for knee pain, and understanding their duration helps place ChondroFiller™ and Arthrosamid® in context.

HA acts as a viscosupplement — it lubricates the joint rather than repairing tissue. Average symptomatic benefit lasts roughly six months, with a range of three to twelve months depending on preparation and individual response; repeat cycles are typically required. Guideline support is mixed: OARSI offers conditional endorsement, while AAOS and ACR guidance is more sceptical. Importantly, HA does not modify cartilage structure.

Corticosteroid injection has a clear and legitimate role in managing acute inflammatory flares or reducing swelling before a procedure. As a durability option, however, relief typically extends only weeks to a few months. The McAlindon et al. 2017 JAMA RCT is worth noting in this context: repeat triamcinolone over two years was associated with measurable cartilage volume loss compared with placebo — a finding relevant to anyone weighing repeated injection cycles as a long-term strategy.

Both options remain appropriate within their proper indications. Their shorter duration simply defines the lower end of the spectrum against which longer-lasting treatments are measured.

Matching treatment to diagnosis, not to durability alone

No head-to-head controlled trial has compared ChondroFiller™ and Arthrosamid® directly, so ranking their durability against each other is not possible from the evidence currently available. That limitation matters less than it might initially appear, because the two treatments do not share an indication.

ChondroFiller™ is assessed for focal, contained defects — typically up to around 6 cm² — where the surrounding cartilage is healthy and the biology of repair is viable. Arthrosamid® is designed for diffuse knee osteoarthritis at Kellgren–Lawrence grade II–IV, where structural repair is not feasible and mechanical cushioning takes priority instead.

Some patients present with both pathologies simultaneously. In that context, clinicians may consider placing both treatments in a single image-guided session — ChondroFiller™ addressing the focal site as the regenerative scaffold component, Arthrosamid® cushioning the broader sub-synovial environment. The two products serve different roles in that combination; they are not interchangeable, and using one does not substitute for the other.

The most useful question for a patient to bring to assessment is therefore not 'which injection lasts longer?' but 'which pathology does my imaging show?' A patient with a focal defect and healthy surrounding cartilage is facing a different durability conversation from one whose imaging shows diffuse grade III–IV OA — and a patient with both faces a third conversation entirely. Identifying which category applies is the work of clinical examination and imaging, not of headline duration figures.

Specialists offering ChondroFiller injection across the UK are listed in the Search MSK directory; filtering by region and treatment type helps identify a consultant with specific experience in this pathway.