The 6 cm² limit — what it means for your eligibility

The single most practical filter for ChondroFiller injection candidacy is defect area: the treatment is indicated for focal articular cartilage defects up to 6 cm². If your scan or clinical assessment shows a defect within that range, you are likely within the treatable window — subject to other criteria covered below.

That 6 cm² ceiling is not an insurance rule or an arbitrary administrative line. It reflects the biological capacity of the collagen scaffold itself — specifically, the area across which the gel can reliably retain position, recruit your own progenitor cells, and support new cartilage formation. The figure is drawn from the CE-marked clinical evidence base underpinning ChondroFiller's Class III device authorisation.

Defects measured above 6 cm² typically indicate diffuse or multi-compartmental joint damage. At that scale, the problem is generally no longer a focal repair candidate — and a different clinical conversation, focused on joint preservation or replacement, becomes more appropriate.

One practical point worth knowing early: MRI-derived defect measurements tend to run smaller than the true area confirmed under image guidance at the time of assessment. If your MRI report describes a defect close to but not quite at the 6 cm² threshold, it is worth discussing with your clinician before drawing conclusions about eligibility.

Area is only half the picture. How deep the defect runs — its ICRS grade — is the parallel criterion, and that is addressed in the next section.

How ChondroFiller's size range compares to other treatments

Cartilage repair treatments have historically been grouped by defect size, with each option covering a different part of the spectrum.

Microfracture and mosaicplasty are typically suited to smaller defects — generally below 2–4 cm². Both are delivered arthroscopically in a theatre setting. Microfracture stimulates marrow bleeding to produce repair tissue, while mosaicplasty transfers small plugs of healthy cartilage from a donor site. Neither is designed for medium-to-large defects.

ACI and MACI — the only other strategies that aim to produce hyaline-like repair tissue — are generally reserved for defects above the 2–4 cm² mark. They require two separate theatre procedures: a first stage to harvest cartilage cells or biopsy tissue, and a second stage weeks later for implantation.

ChondroFiller injection, delivered as an ultrasound-guided outpatient procedure, is indicated up to 6 cm². That range spans both bands: it covers the smaller defects that microfracture typically addresses and extends into the medium-to-large territory that has previously required two-stage cell-based surgery.

| Treatment | Typical size range | Procedure type | |---|---|---| | Microfracture / Mosaicplasty | < 2–4 cm² | Single-stage, theatre | | ACI / MACI | > 2–4 cm² | Two-stage, theatre | | ChondroFiller injection | Up to 6 cm² | Single-stage, outpatient |

For patients with defects in the 2–6 cm² range, ChondroFiller injection offers a single-stage, image-guided option that sits in a lane the field had not previously filled. That said, individual suitability depends on more than size alone — defect depth, joint condition, and overall health all factor into whether any one approach is appropriate.

Defect depth: why ICRS grade runs alongside area

Area tells you how wide a defect is; grade tells you how deep it goes. Think of it like a pothole: the diameter matters, but so does whether it has worn through the tarmac into the substrate beneath. ChondroFiller injection is designed for defects that have done exactly that — penetrated beyond the halfway point of the cartilage layer.

In clinical terms, this means ICRS Grade III or Grade IV lesions. Grade III defects extend more than 50% of the cartilage's full thickness, sometimes reaching the calcified base layer without fully breaching it. Grade IV lesions go further still, exposing the subchondral bone beneath. The scaffold is engineered for this level of structural loss — surface irregularities or partial-thickness wear (Grade I–II) generally fall outside the indicated range, because the gel needs substantial depth to retain position and allow cell recruitment to proceed correctly.

One additional criterion matters at all depths: the cartilage surrounding the defect should be healthy and intact. The scaffold anchors against those borders; without them, reliable integration is harder to achieve.

Grade IV bone involvement may affect how your assessment is planned — whether any preparatory step is needed before the injection — but this is determined individually and should not be a source of alarm. Your clinician will establish both grade and area together, using high-resolution MRI and, where needed, image-guided assessment. Knowing your ICRS grade, not just the size figure, gives a fuller picture of where you stand.

The 3–6 cm² zone: where the treatment decision gets interesting

Research from the SUMMIT randomised controlled trial introduced a secondary benchmark that reshapes how medium-to-large defects are managed: 3 cm². Above this threshold, MACI produced significantly better KOOS pain and function scores than microfracture at both two and five years — making the 3–6 cm² band, by default, MACI territory.

For patients in this range, the question has therefore not just been "which material?" but "how much am I taking on?" MACI's evidence is substantial, yet the pathway requires two separate hospital visits: an initial biopsy stage, a cell-culture waiting period, then a second procedure for implantation.

ChondroFiller injection covers this entire 3–6 cm² band in a single outpatient session under image guidance. The distinction matters not because outcomes are guaranteed to match, but because treatment burden and access are real components of any decision. Fewer hospital visits, no interim waiting stage, and an outpatient setting rather than a theatre list are considerations that carry weight — particularly for patients who are working, caring for others, or facing extended waiting times.

Suitability within this zone still depends on a full individual assessment. Defect grade, surrounding cartilage quality, and overall joint condition all factor into what a consultant will recommend.

MRI measurements and what your scan result actually tells you

The gap between what a scan shows and what is confirmed at clinical assessment tends to run between 10 and 30%. In practical terms, a lesion reported as 5.5 cm² on MRI could measure closer to 4 cm² — well within the indicated range for ChondroFiller injection — once assessed directly.

This matters most for patients sitting near the 6 cm² ceiling. A radiology report that reads borderline should not prompt self-exclusion; it should prompt a clinical conversation. The threshold applied at the time of assessment uses confirmed measurements, not estimates from a scan taken weeks earlier.

MRI remains essential at every stage — it characterises how deep the lesion goes, evaluates the subchondral bone beneath, and maps the health of the surrounding cartilage. Those contributions to treatment planning are significant. Defect area is simply where MRI is at its least precise, and it happens to be the number patients focus on most.

If your scan puts you close to a size boundary in either direction, a specialist review — not the radiology letter — is what determines next steps.

What the outcomes data shows — and where evidence is still developing

Published imaging data provides the clearest picture of what ChondroFiller injection achieves structurally. MOCART scores — a validated MRI measure of repair tissue quality — averaged 81.6 at one year, indicating that more than 80% of the treated defect area had filled with new repair tissue. That figure held across the indicated size range, not only in smaller lesions. Functional outcomes followed a similar pattern: IKDC scores improved by approximately 30 points from baseline across clinical studies, a gain that substantially exceeds the minimum clinically important difference of 16.7 points.

What the evidence has not yet established is whether outcomes vary within the 6 cm² range. No published sub-group data currently stratifies results by defect size — comparing, for instance, lesions below 2 cm² against those in the 4–6 cm² band. Finer-grained size comparisons remain a research frontier rather than answered questions.

The data that exists does not point to an efficacy cliff at the upper end of the indicated range. The 6 cm² ceiling appears to reflect the scaffold's biological capacity — the point beyond which a different repair strategy is warranted — rather than a zone where performance begins to decline. For patients and clinicians working with medium-to-large defects, that distinction matters: the current evidence base is developing, but it is not equivocal.