Am I a suitable candidate?

Most adults with cartilage damage fall into one of two groups that ChondroFiller injection is designed to help. The first is a focal, contained defect — a discrete area of cartilage loss graded ICRS or Outerbridge III or IV, where damage extends through more than half the cartilage thickness or reaches the underlying bone. The second is more widespread joint degeneration, where the injectable collagen scaffold acts as a viscoelastic cushion across a broader articular surface rather than filling a single bounded lesion.

A common point of confusion is worth correcting early: a 'bone on bone' finding on a plain X-ray does not automatically rule out treatment. Kellgren-Lawrence Grade III–IV presentations — including those labelled bone on bone — may still be suitable via the diffuse osteoarthritis injection track, provided the clinical picture supports it. The X-ray alone is never the deciding factor.

Three lesion types tend to be particularly well matched to this treatment: focal chondral lesions, osteochondritis dissecans, and defects that have developed following meniscal injury or prior ligament reconstruction. Age, on its own, is not a disqualifying criterion on the injection pathway.

MRI is the non-negotiable starting point. It confirms whether the damage is focal or diffuse, measures defect geometry, and identifies any features — such as widespread joint degeneration or subchondral bone pathology — that would redirect care. A consultation without MRI cannot reliably determine which track, if either, applies.

How cartilage grading shapes eligibility

Cartilage damage is graded on a four-point scale — Outerbridge, also expressed as ICRS grading — that describes how far through the cartilage layer the damage extends. Grade I is surface softening or blistering with the cartilage still intact; Grade II is partial-thickness loss reaching less than halfway down. At Grade III, the damage passes beyond the midpoint of the cartilage depth; at Grade IV, the cartilage is gone entirely and the underlying bone is exposed.

The focal-defect track for ChondroFiller injection targets Grade III and IV lesions specifically. The reasoning is straightforward: at these grades, the structural loss is significant enough to warrant regenerative intervention, yet the defect remains bounded. That containment matters because the injectable collagen scaffold relies on intact surrounding cartilage walls to gel in place and hold its shape while host cells migrate into the matrix.

Grades I and II represent real damage — and can be genuinely painful — but they sit below the threshold where the focal-defect pathway applies. Assessment at those stages may point towards other management options.

Stable joint mechanics are just as important as the grade itself. Untreated ligament laxity, significant limb malalignment, or an active meniscal deficit can undermine the biological environment the scaffold depends on. These are relative exclusions, not permanent disqualifiers: addressing instability or alignment before or alongside treatment often brings a patient back into consideration for the injection pathway.

Defect size and where ChondroFiller injection fits

The 6 cm² ceiling on the focal-defect track is clinically meaningful once it is placed alongside the alternatives. Microfracture is generally suited to lesions below 2–4 cm²; beyond that size, outcomes tend to deteriorate. Cell-based procedures such as MACI can handle larger defects but require two-stage surgery — a first procedure to harvest chondrocytes, a culture period, then a second implantation visit. ChondroFiller injection occupies the practical middle ground: a single-stage, ultrasound-guided outpatient procedure across defects up to 6 cm², where microfracture is no longer appropriate but two-stage cell therapy feels disproportionate to the clinical picture.

On the diffuse osteoarthritis track, size works differently. There is no fixed ceiling because the injectable collagen scaffold coats the articular surface broadly rather than filling a discrete lesion — making this pathway accessible to patients with Kellgren-Lawrence Grade III–IV wear who have already been told they are beyond the scope of focal repair.

Defect geometry still matters, though, even where size is not the gate. MRI measurements inform the appropriate syringe volume before treatment — one reason imaging is assessed beforehand rather than estimated in clinic.

Clinical decisions across both tracks draw on four dimensions: joint mechanics; the biological repair environment; tissue chemistry — meaning the joint's inflammatory and metabolic state, including any underlying conditions that may impair healing capacity; and disease timing — how long the damage has been present and whether earlier procedures have already altered the repair environment. Defect size is one input within this framework, not a standalone verdict.

When ChondroFiller injection is not the right option

Three situations place a patient outside ChondroFiller injection candidacy — two are hard contraindications, one is conditional.

A known allergy to collagen of bovine, porcine, or murine origin is an absolute contraindication. The scaffold itself is murine-derived Type I collagen; an immune reaction to the material would compromise both safety and any prospect of integration.

Metabolic arthropathy — including active gout or calcium pyrophosphate disease — is a formal contraindication for the same biological reason. When the joint's chemical environment is driven by crystal deposition or systemic metabolic dysfunction, the conditions progenitor cells require to migrate into and remodel the scaffold cannot reliably be met.

Advanced pan-articular osteoarthritis, where degeneration spans the whole joint surface, lies outside the focal-defect track. The diffuse-OA injection pathway may still be appropriate in some such cases — that depends on individual clinical assessment — but widespread structural loss is not what the contained-defect indication is designed to address.

Joint instability and malalignment were covered in the previous section; where those issues can be corrected, eligibility often changes.

Safety record and realistic outcome expectations

Across manufacturer-sponsored clinical investigations, ChondroFiller injection carries a complication rate of approximately 0% and a reoperation rate of 3–8%. For context, microfracture carries a reoperation rate of up to 41%, and MACI — which involves two surgical procedures — has reported complication rates of up to 17% and reoperation rates of up to 37%. The safety margin here is substantial, not marginal.

The one meaningful technique-specific risk is fibrous tissue formation, identified in the 2025 prospective PMC study by Demmer et al. in 25 wrist cases. The finding was precise: fibrous tissue formed only in defects that had been overfilled. Defects treated with a flush application — material level with the surrounding cartilage surface — showed no fibrous tissue formation at all. This makes delivery accuracy the governing variable rather than the product itself, and it is one reason that the skill and experience of the clinician administering the injection matters.

Functional outcomes in the knee give patients a concrete benchmark. IKDC scores improve by approximately 30 points over one to three years — the Jerosch et al. post-market clinical follow-up study recorded a mean improvement of 32.4 points, sustained at three years, with patients reaching a functional score of 80. The minimum clinically important difference on the IKDC scale is 16.7 points, so these results represent meaningful, measurable gain rather than statistical noise. MOCART imaging scores of 81.6–84.3 at follow-up MRI confirm more than 80% defect fill with good structural integration.

Two evidence gaps are worth naming honestly. Long-term follow-up data beyond three years in the knee remains limited, and head-to-head randomised controlled trials comparing the outpatient injection pathway against surgical alternatives have not yet been published. The evidence to date is consistently positive and continues to grow — the Demmer 2025 wrist study, for example, is the first peer-reviewed report for small joints — but patients should understand this is a developing picture rather than a decades-old dataset.

Getting assessed at the London Cartilage Clinic

Reaching a clear candidacy answer requires reviewing imaging alongside a clinical examination — the two together determine which eligibility track applies and whether defect geometry and joint mechanics support proceeding. That combined assessment is what the initial consultation at the London Cartilage Clinic on Harley Street is built around: MRI is interpreted in context, the focal or diffuse pattern is confirmed, and joint-specific timing is discussed in a way that generic referral pathways rarely allow.

ChondroFiller injection is offered across a range of joints at the clinic — knee, hip, ankle, shoulder, elbow, wrist, thumb, and small hand joints — so patients whose damage falls outside the knee should not assume the pathway does not apply to them.

Professor Paul Y. F. Lee, who leads Liquid Cartilage™ delivery in the UK, places particular emphasis on application precision. As the Demmer 2025 findings make clear, flush delivery — material level with the surrounding cartilage surface — is a meaningful determinant of outcome; the same product can produce different results depending on how it is administered.

Patients who have gathered sufficient information and wish to discuss individual circumstances can book an assessment at londoncartilage.com.