The short answer to candidacy

For many patients arriving at this question, the worry is the same: 'My cartilage damage is severe — have I already missed the window?' The straightforward answer is that ChondroFiller® (also marketed as Liquid Cartilage™) is specifically designed for significant cartilage damage. Candidacy opens at ICRS Grade III, where more than half the cartilage depth has been lost, and extends to Grade IV, where the cartilage is gone entirely and bone is exposed. That severity is the target, not a barrier to treatment.

Age is not an exclusion criterion. Even patients who have been told they are 'bone on bone' may still be suitable — what matters is the pattern and location of the damage, the state of the surrounding joint, and whether certain structural and health criteria are met.

The treatment itself is delivered as an ultrasound-guided outpatient injection — a collagen scaffold placed precisely into the defect under imaging guidance, without surgical admission.

Candidacy is criteria-based, however, and cannot be confirmed without an MRI scan and a clinical specialist assessment. The sections below set out what those criteria actually involve.

How cartilage damage is assessed for eligibility

Confirming eligibility requires two things that clinical examination alone cannot provide: an MRI scan and a structured grading of the damage it reveals.

MRI and ICRS grading

MRI maps defect location, depth, area, and — critically — the quality of the cartilage tissue immediately surrounding the lesion. That surrounding tissue is not incidental: the collagen scaffold works by recruiting the patient's own progenitor cells, and those cells migrate from adjacent healthy or viable cartilage and subchondral bone. Thin, degraded borders reduce the scaffold's ability to initiate that repair process.

The ICRS (Outerbridge) grading scale is the clinical framework used to interpret what the MRI shows. Grades I and II — surface softening or partial-depth fissuring — generally represent damage that is too mild to warrant ChondroFiller at this stage. Grades III and IV, as noted by specialists using the product, mark the threshold where the scaffold becomes clinically relevant. Grade I–II changes are typically managed through other conservative or palliative routes first.

Defect size and the injectable route

Once ICRS grade is established, defect size shapes which delivery approach is appropriate. For the injectable outpatient pathway — ultrasound-guided placement without surgical admission — a focal 'pothole' lesion, typically in the region of 1.5–3 cm², is the primary indication. Scaffold volume is matched to defect dimensions using a sizing guide rather than a fixed dose.

It is worth being clear that an exact universally published upper size limit for the injectable route does not appear in current clinical documentation. The specific threshold for any individual patient is part of the specialist assessment conversation, not a number to confirm in advance.

When damage is more diffuse

Not every patient presents with a single contained defect. In cases of more widespread joint degeneration — Kellgren-Lawrence Grade III or IV osteoarthritis — the clinical picture shifts. Here the scaffold may be used less as a focal patch and more as a surface-coating cushion, supporting the remaining joint structures across a broader area rather than filling one discrete void. This is a meaningfully different clinical mode, and the assessment criteria applied to it differ accordingly. Patients in this category should expect their specialist to discuss whether focal repair, the cushioning approach, or a combination pathway is most appropriate for their imaging findings.

Structural and lifestyle prerequisites

Even when the cartilage damage qualifies on imaging, the joint housing it must be in adequate mechanical order. Think of an unstable joint as a leaky bucket: placing a scaffold into a space that shifts unpredictably under load gives the repair material little chance to integrate properly before it is dislodged or deformed.

In practical terms, this means intact ligament support — including the ACL and MCL in the knee — and joint alignment that falls within approximately 5° of neutral. Malalignment beyond that range places asymmetric load on the repair site throughout every step the patient takes. Where significant meniscal damage is also present, this is typically addressed at the same time or before the injection: untreated meniscal instability creates the same undermining effect as ligament laxity.

A period of conservative care is the second structural prerequisite. Physiotherapy, analgesic medication, and other non-surgical interventions should have been tried and found insufficient before ChondroFiller injection is considered. This is not a gatekeeping formality — it ensures that patients are at a stage where an active repair intervention is genuinely the appropriate next step.

Body weight is a consistent factor in published outcome data: patients who maintain a healthy weight reduce the mechanical stress on the repair environment, which is associated with more favourable results.

Finally, recovery from a ChondroFiller injection requires a structured non-weight-bearing period followed by guided rehabilitation. Patients who are unable or unwilling to follow this protocol are unlikely to achieve the benefit the scaffold can offer — an important clinical consideration that a specialist will discuss openly at assessment.

Absolute contraindications

Several conditions rule out ChondroFiller regardless of how severe the cartilage damage is or how otherwise suitable the patient might appear. Checking these before a specialist appointment saves time and sets realistic expectations.

• Hypersensitivity to Type I collagen or murine (rat) proteins. The scaffold is derived from murine sources, so any known allergy to these proteins is an absolute bar. Allergy history should be declared at the earliest opportunity.
• Active joint infection. Placing any implanted scaffold into an infected environment risks seeding and worsening the infection. The joint must be free of active infection before treatment can be considered.
• Inflammatory arthritis — including rheumatoid arthritis. Where the joint is being damaged by an ongoing inflammatory process, the scaffold cannot integrate as intended. The underlying disease would continue to erode the repair environment.
• Haematopoietic (blood) disorders. Conditions that impair normal cell production or clotting affect the biological environment the scaffold depends on.
• Active malignancy. Cancer in any active phase is a contraindication, consistent with standard practice for implanted medical devices.
• Metabolic arthropathy — for example, gout during an active phase. Crystal-driven joint damage represents the same problem as inflammatory arthritis: the joint environment is hostile to scaffold integration.
• Pregnancy and breastfeeding. Safety data in these groups has not been established, making them absolute contraindications.

These are standard clinical safety checks rather than unusual restrictions. Any patient with a relevant history should discuss it at their initial assessment; in most cases the specialist can clarify quickly whether it applies.

Which joints and body regions ChondroFiller injection covers

The scaffold's reach extends across a wide range of joints, though the depth of supporting evidence varies considerably by region.

Knee is where the clinical record is most mature. Published European studies report IKDC score improvements of approximately 30 points and MOCART structural regeneration scores in the 81–84 range, with more than 19,000 cases performed globally. For patients with knee cartilage damage, this volume of real-world use means that outcome expectations can be grounded in robust data.

Hip has solid peer-reviewed backing. Mazek et al. (2021) published a study of ChondroFiller gel used during hip arthroscopy — including cases related to femoroacetabular impingement (FAI) — and reported Harris Hip Score improvements of approximately 33 points. That study used arthroscopic delivery; in the current injectable pathway, the hip represents an established clinical target with outcomes data supporting its use for suitable focal lesions.

Ankle is a recognised and growing application with established clinical use, though published outcome series are less extensive than for the knee.

Shoulder, elbow, wrist, thumb base (CMC joint/rhizarthrosis), and foot are all recorded application sites. Wrist use includes residual cartilage defects following distal radius fractures, where post-treatment imaging has shown joint space widening and reduced bone marrow oedema. Shoulder outcomes have been measured using NRS pain scores and the DASH questionnaire. Across these smaller joints, the evidence base is more case-series in nature and less mature than the knee and hip data.

In every region, the underlying mechanism — acellular matrix-induced chondrogenesis, in which the scaffold recruits the patient's own progenitor cells — remains the same. What differs is the accessibility of the target site and how much published data sits behind that particular application.

Getting assessed for ChondroFiller injection

Getting started does not require a GP referral, though many patients arrive through one. Self-referral to a specialist MSK or orthopaedic clinic is a straightforward option, and the initial process is less complicated than most patients expect.

If you already have an MRI scan of the affected joint, bring it — or arrange for images to be transferred before your appointment. Recent imaging often allows the specialist to move directly to a clinical assessment rather than repeating a scan unnecessarily, which speeds up the candidacy review.

The assessment itself typically covers three areas: review of any existing MRI findings against the ICRS grading criteria, a physical examination of joint stability and alignment, and a structured conversation about which conservative treatments have already been tried and to what effect. That clinical picture — not an online checklist — is the basis on which suitability is confirmed.

For patients found to be suitable, the injectable pathway is an outpatient appointment rather than a surgical admission. No theatre booking or overnight stay is involved.

Patients looking for a specialist who offers ChondroFiller or Liquid Cartilage injection in their area can use the Search MSK directory, which covers clinicians across the UK and can be filtered by region, joint, and treatment type.