The candidacy question most patients ask first

"Am I suitable for ChondroFiller?" is the question most patients bring to their first cartilage consultation — and it has a clear, structured answer. Suitability rests on three interlocking criteria: the size of the cartilage defect, the grade of wear or osteoarthritis across the joint, and whether the joint's alignment and mechanics are stable. Meet those criteria, and either the injectable scaffold pathway or the surgical liquid cartilage route — or both — may be appropriate. Miss one, and a different treatment or a preparatory step is likely needed first.

The injectable collagen scaffold pathway is delivered as an ultrasound-guided outpatient injection, placing it within reach of patients who are not surgical candidates. There is no upper age limit on the injection route; it is used in active patients in their 60s, 70s, and beyond as a joint-preservation option before any consideration of replacement.

No single criterion settles the question alone. Defect size and OA grade interact, and alignment status can alter what is — or is not — appropriate to treat. A structured specialist assessment is the only reliable way to map those factors against the available pathways and confirm which one fits a given patient's joint.

How defect size affects suitability

Defect size shapes the candidacy conversation differently depending on which pathway is under consideration. For conventional options described in the literature, it functions as a hard selector: microfracture is generally reserved for lesions below 2–4 cm², while cell-based therapies such as ACI or MACI become the preferred option above that range. The SUMMIT trial clarified the clinical significance of that divide — patients with defects of ≥3 cm² achieved superior KOOS outcomes with MACI over microfracture at both two- and five-year follow-up, which is why the field distinguishes smaller focal lesions from larger ones so carefully.

The injectable ChondroFiller scaffold pathway does not carry an equivalent size ceiling. The collagen matrix is introduced as a liquid that gels in situ, so it can be placed across a contained focal lesion or distributed across a wider articular surface area within a single clinical appointment. That characteristic means patients who fall outside the defect-area range where marrow stimulation is considered adequate — or who are not candidates for a cell-based procedure — remain eligible for the injectable route on defect-size grounds alone. Size, in other words, does not disqualify a patient from this pathway in the way it limits the alternatives.

Absolute area is not, however, the only geometric variable that matters. Defect location — whether the lesion sits in the weight-bearing zone of the medial condyle, the trochlea, or a less-loaded region — and containment by intact, healthy cartilage borders on all sides both influence whether the repair scaffold can integrate properly. An uncontained lesion, or one in a high-shear zone without stable surrounding tissue, warrants careful assessment even when the measured area sits comfortably within a treatable range.

OA grade and where ChondroFiller fits on the severity scale

Cartilage grading tells a different story from defect area — it describes how severely the tissue itself has deteriorated, not how large the affected zone is. On the ICRS scale, Grade III lesions penetrate more than 50% of cartilage depth; Grade IV extends through the full thickness to subchondral bone. The Kellgren-Lawrence (KL) radiographic system maps that same progression on plain X-ray, with Grade III and IV representing moderately and severely reduced joint space — the latter commonly described as 'bone on bone'.

The injectable ChondroFiller scaffold pathway covers this full range. For isolated focal ICRS Grade III–IV defects with structurally intact surrounding borders — where the scaffold can integrate into well-contained tissue — the injectable route addresses the lesion directly. Where damage has progressed to KL Grade III or IV osteoarthritis, with more diffuse surface wear, the pathway remains available and the clinical protocol adapts rather than the door closing.

For KL Grade III/IV OA, a dual-injection approach may be employed: ChondroFiller — the acellular collagen scaffold that recruits the patient's own progenitor cells via matrix-induced chondrogenesis — alongside Arthrosamid, a permanent hydrogel that acts as a cushioning agent within the joint space. The two products serve mechanistically distinct roles and should not be conflated: ChondroFiller is the regenerative scaffold component; Arthrosamid is not. In the most advanced end-stage cases, a tri-active protocol adds autologous mesenchymal stem cells to that combination. For patients with progressive OA who are not yet surgical candidates or who decline replacement, a bi-annual ChondroFiller top-up is offered as part of a longer-term joint-preservation programme.

Clinical outcomes across this spectrum are grounded in published data. In the prospective PMCF study by Jerosch et al., the scaffold achieved a mean IKDC improvement of 32.4 points sustained to three-year follow-up — comfortably above the recognised 16.7-point minimum clinically important difference. MRI-based MOCART scores in European studies range from 81.6 to 84.3, indicating consistent structural integration of repair tissue across treated joints.

Why joint alignment must be addressed before treatment

Before the scaffold can do its work, the mechanical environment it is placed into must be sound. Joint alignment is assessed as part of every ChondroFiller candidacy evaluation — not as a scored threshold with a published degree cut-off, but as a biomechanical prerequisite that determines whether the repair environment is viable.

The rationale is straightforward: ChondroFiller addresses the cartilage defect itself, not the force distribution driving it. Placing a collagen scaffold into a compartment carrying asymmetric load — from uncorrected varus or valgus — would expose the repair tissue to the same mechanical stress that accelerated cartilage loss in the first place. The scaffold gels and integrates in situ; it cannot correct the forces acting on it.

What a specialist is weighing in practice is whether the patient's alignment is changing where load falls across the defect site — whether, for this patient's gait, weight, and defect location, the repair zone will be protected or persistently over-stressed. That assessment draws on clinical examination, gait observation, and imaging together; it resists reduction to a single angle measurement, which is why the suitability criterion is framed as 'no significant malalignment' rather than a specific degree threshold.

Where meaningful malalignment is identified, corrective osteotomy or stabilisation is typically addressed before or alongside treatment — making this a staging consideration rather than a permanent exclusion. Untreated ligament instability and meniscal deficit driving the wear carry the same logic as parallel prerequisites: each represents a mechanical cause that ChondroFiller is not designed to resolve, and each should be corrected so that the regenerative scaffold has a stable, appropriately loaded environment in which to work.

Age, joint type, and underlying cause of damage

Age is not a barrier on the injectable pathway — as the opening section noted — and the range of treatable joints is correspondingly broad: hip, ankle, shoulder, elbow, wrist, foot, and hand all sit within scope alongside the knee.

The underlying cause of cartilage damage carries more weight in the candidacy conversation than age does. Post-traumatic chondral lesions, osteochondritis dissecans (OCD), and damage arising secondary to meniscal tear or ligament reconstruction are recognised indications, provided the primary structural problem has already been addressed. A joint that has undergone ligament reconstruction, for instance, may still carry a residual focal chondral lesion that ChondroFiller® can target — so long as the reconstructed joint is otherwise stable and mechanically sound. The operative question is whether the wider joint environment, after accounting for any prior injury or repair, will support regenerative treatment.

Formal contraindications — collagen sensitivity and active infection are two examples — are confirmed individually at clinical assessment rather than through a standardised public checklist.

Getting a candidacy assessment at the London Cartilage Clinic

What a formal assessment adds to the picture is something an article cannot provide: a verdict for a specific joint. Imaging — MRI to characterise the lesion, X-ray to establish OA grade and alignment — is reviewed alongside clinical examination and a conversation about activity goals, so that each candidacy gate is applied to the patient's actual anatomy rather than to a generalised profile.

In practice, alignment is the gate that most often generates surprise in consultation. Patients who expect defect size or OA grade to be the deciding factor sometimes discover that a correctable mechanical issue — varus drift, a residual ligament deficit — is what needs to be addressed first. That is a staging consideration, not a permanent exclusion, and identifying it early is part of what a structured assessment is for.

Professor Paul Y. F. Lee leads ChondroFiller® candidacy assessment at the London Cartilage Clinic's Harley Street practice, with experience spanning the full range of defect profiles, OA grades, and joint types described in this article. To find out whether ChondroFiller® is suitable for your joint, book a consultation at londoncartilage.com.