The short answer: what ChondroFiller is designed to treat

Not everyone with joint pain will be suitable for ChondroFiller injection — but the range of patients who may qualify is broader than many expect, and it does not map neatly onto pain severity alone.

ChondroFiller (also marketed as Liquid Cartilage) is an acellular collagen scaffold administered as an outpatient ultrasound-guided injection, not a surgical or arthroscopic procedure. Once placed, it gels in situ and recruits the body's own progenitor cells to support endogenous repair — a process known as acellular matrix-induced chondrogenesis. The practical starting point for any assessment is structural, not symptomatic: MRI-confirmed cartilage damage and documented failure of conservative management are the two gateway criteria that open the door to more detailed triage.

Beyond those prerequisites, candidacy follows one of two distinct clinical tracks. Where damage is contained within a discrete, bounded area, the focal defect pathway applies. Where degeneration is more widespread — including Kellgren-Lawrence Grade III or IV osteoarthritis — a separate diffuse OA logic governs whether injection is appropriate. These tracks are not interchangeable, and the section below unpacks each in turn.

Age, on its own, is not a barrier. Suitability turns on the grade and geometry of cartilage loss and the mechanical condition of the joint, not on how many years a patient has had symptoms.

Cartilage damage criteria: grading and the two clinical tracks

Damage grade sits at the centre of ChondroFiller candidacy — and for good reason. The Outerbridge (ICRS) scale runs from Grade I (surface softening only) through to Grade IV (full-thickness loss exposing the underlying bone). ChondroFiller injection is indicated from Grade III upwards: partial-thickness damage penetrating more than half the cartilage depth, or the full-thickness loss of Grade IV where subchondral bone is directly visible on MRI. Grades I and II, where the cartilage surface remains relatively intact, fall below the treatment threshold.

The focal defect track

Grade III or IV damage that is discrete and spatially contained — a bounded patch with identifiable edges and healthy surrounding cartilage — is assessed on the focal defect pathway. Here, the scaffold is placed to fill the lesion directly. The standard published indication covers defects up to 3 cm²; the CE mark extends eligibility to focal lesions up to 6 cm². Post-traumatic injuries and osteochondritis dissecans often produce exactly this pattern.

The diffuse osteoarthritis track

Where degeneration is more widespread — Kellgren-Lawrence Grade III or IV, including bone-on-bone presentations — the clinical logic changes. Surgery may have been declined or judged non-viable, yet injection can still be appropriate. In this setting the scaffold is not filling a discrete hole; it functions as a viscoelastic coating across the articular surface, providing a protective layer rather than structural restoration.

MRI is non-negotiable for track assignment. Symptom pattern and X-ray appearances alone cannot determine defect geometry or confirm which pathway applies — that mapping requires cross-sectional imaging before any treatment decision is made.

What must be tried first: the prerequisite hurdles

Before defect-specific triage begins, two criteria must be satisfied — and neither is about how severe the pain feels on a given day.

The first is documented failure of conservative management. A clinician will want to see that standard treatments have been tried and found insufficient: a structured physiotherapy programme, load modification, and at least one prior injection such as hyaluronic acid or a corticosteroid. This is not a bureaucratic hurdle; it reflects sound clinical logic. ChondroFiller is most likely to benefit patients for whom those measures have genuinely been exhausted, not bypassed.

The second is MRI-confirmed structural damage. Weight-bearing X-rays and symptom scoring are useful, but imaging is the only reliable way to confirm defect grade, map lesion geometry, and flag structural contraindications — including malalignment or ligament instability — that would need addressing before any scaffold injection could succeed.

The interplay between these two criteria catches a common misconception: that severity of pain should be the primary yardstick. Clinically, it is not. A patient with moderate, manageable discomfort may fully satisfy the structural entry criteria; a patient in significant daily pain may not, if the underlying cartilage picture falls outside the treatable window. Structural assessment drives the decision — not the symptom score.

Presentations that respond best

The presentations that respond most clearly share a common thread: a definable cause, mechanically sound surrounding joint, and a patient with something specific to protect.

Post-traumatic chondral lesions sit at the top of the list. A sports injury, a direct impact, or a shear force that creates a discrete defect in an otherwise stable joint is close to the archetypal focal-pathway indication — the lesion has edges, the surrounding cartilage is relatively intact, and mechanics are addressable. Osteochondritis dissecans produces a structurally similar picture and is equally well-matched to this approach.

The broader archetype is the active adult who wants to preserve joint function and delay — or entirely avoid — a joint replacement. No strict upper age limit applies; suitability turns on joint integrity, defect character, and general health rather than chronological age. A motivated 65-year-old with a focal Grade IV lesion and stable ligaments may be a stronger candidate than a younger patient with diffuse wear and unaddressed malalignment.

Patients with Kellgren-Lawrence Grade III or IV osteoarthritis who have been advised against surgery, or who have made an informed decision to pursue non-surgical management, may also be suitable via the diffuse OA track. This pathway is specifically for patients outside the surgical window — it is not a fallback route for anyone with joint pain and a normal X-ray. The clinical distinction between a scaffold placed as a targeted fill and one applied as a viscoelastic surface coating is meaningful, and it shapes both the assessment process and what a realistic outcome looks like.

Contraindications and structural exclusions

Several categories of patient fall outside the ChondroFiller indication, and these are worth understanding clearly — both for those self-referring and for GPs or physiotherapists making a referral.

Absolute contraindications

• Hypersensitivity to murine proteins or collagen. ChondroFiller is a murine-derived (rat-origin) Type I collagen scaffold. Any known or suspected allergy to rat-derived proteins or collagen components is an absolute bar to treatment.
• Active infection. This covers both local infection in or around the target joint and active systemic infection. Introducing a scaffold into an infected environment carries serious risk and is not appropriate.
• Active inflammatory joint disease flare. A rheumatoid arthritis flare or acute gout attack excludes injection at that time. Stable, well-controlled inflammatory arthritis is a different situation and can be assessed on a case-by-case basis — the key distinction is disease activity at the point of treatment, not diagnosis alone.
• Periarticular tumours or malignancies. Any confirmed or suspected tumour in or around the joint is a contraindication.

General health exclusions

Pregnancy and breastfeeding exclude treatment. Active haematological disorders or uncontrolled clotting abnormalities are also grounds for exclusion.

Structural and mechanical exclusions

Three joint-level problems preclude ChondroFiller injection unless addressed first:

• Uncorrected malalignment greater than 5°. The scaffold cannot compensate for abnormal load distribution. If the joint is mechanically misaligned, the repair environment is compromised and the injection is unlikely to hold its therapeutic benefit.
• Unresolved ligament instability. A ruptured ACL or MCL that has not been treated creates ongoing mechanical disruption that undermines scaffold integration.
• Severe arthrofibrosis. Significant intra-articular fibrosis restricts joint movement and limits the fluid environment the scaffold requires to gel and function correctly.

In some cases these structural issues can be addressed before or alongside ChondroFiller; in others they are a definitive barrier. A formal clinical assessment — including MRI, weight-bearing X-rays, and direct examination — is what determines which applies to any individual presentation.

What happens after you are assessed as a candidate

Confirming candidacy is the beginning of the clinical process, not the end of it. Once assessment establishes that the structural, mechanical, and health criteria align, the next step is triage into a treatment track suited to the specific presentation.

For most patients with a focal or moderate defect, the pathway centres on ChondroFiller as the primary scaffold injection — placed under ultrasound guidance in an outpatient setting, with the goal of supporting the joint's own repair processes through acellular matrix-induced chondrogenesis. The track chosen at assessment — broadly described as Prevention, Regeneration, Combination, or Support — reflects how much damage is present, how widely it is distributed, and how much structural reserve the joint retains.

More advanced presentations, including Kellgren-Lawrence Grade III or IV disease that has already been discussed in the section above, may require combination therapy. In that context, ChondroFiller serves as the regenerative scaffold element, while a co-administered agent such as Arthrosamid — a permanent polyacrylamide hydrogel — is used for a mechanically distinct purpose: synovial cushioning rather than tissue repair. These are different treatments working through different mechanisms, and they are not interchangeable components of a single combined 'filler'.

Formal assessment at London Cartilage Clinic, based on Harley Street, is the starting point for mapping which track applies. Patients outside London may be directed to affiliated MSK Doctors sites. To arrange an initial consultation, visit londoncartilage.com.