What the candidacy question actually comes down to

Most patients researching ChondroFiller injection arrive expecting a straightforward yes or no. The clinic assessment does not work that way — it is a routing conversation, not a binary pass/fail screen.

ChondroFiller injection is an ultrasound-guided outpatient treatment that delivers an injectable collagen scaffold into the damaged joint. Once in place, the scaffold gels and recruits the patient's own progenitor cells to promote new cartilage formation through a process called acellular matrix-induced chondrogenesis. Because the assessment is about matching the right protocol to the joint rather than disqualifying patients outright, a much wider range of presentations falls within scope than many patients expect — including those with advanced osteoarthritis who have been told surgery is their only remaining option.

Candidacy turns on four filters: defect size, Kellgren-Lawrence (KL) grade, joint alignment and stability, and prior treatment history. None of these filters carries the blanket exclusions found in surgical cartilage repair programmes such as ACI or microfracture. Instead, each filter routes the patient to the appropriate treatment tier. The sections that follow examine each filter in turn.

Does defect size change your options

There is no defect size that automatically rules a patient out of ChondroFiller injection. As an ultrasound-guided injectable, the collagen scaffold can be delivered to coat the full articular surface in a single session — dosing scales by volume rather than by measured defect area, with most patients treated using one box and larger or multi-compartment presentations addressed with two or three.

At assessment, the clinical team will use ICRS grading to describe the defect's depth (Grade 2 through 4, from partial to full-thickness loss) and may reference area benchmarks — commonly 2–4 cm² — that patients sometimes encounter in research or referral letters. These figures are worth understanding, because they define the thresholds that govern surgical options: microfracture is typically indicated for defects below 2–4 cm², whilst ACI and MACI are directed at larger lesions above that range. Each carries a fixed area constraint that leaves some patients outside the eligibility window of either procedure.

ChondroFiller injection sits outside that surgical framework. The threshold that shaped those operative techniques does not apply to an injectable scaffold.

What defect burden does influence is treatment planning. A particularly large or multifocal pattern may prompt discussion of additional units or, in advanced presentations, a combination approach. Size informs dosing and protocol; it does not determine eligibility.

OA grade and KL stage — where each patient sits in the protocol

Kellgren-Lawrence grade does not disqualify a patient from ChondroFiller injection — it routes them to the right protocol tier.

That distinction matters because many patients arrive having been assessed under a different framework. Surgical cartilage repair programmes such as ACI and microfracture carry hard OA grade ceilings, and patients with KL III–IV disease are often turned away as a result. ChondroFiller injection operates differently: presentations across KL 0–IV each map to a specific treatment approach rather than a pass/fail verdict.

Early-to-moderate wear (KL 0–II, focal defect): a standalone ChondroFiller injection is the standard starting point. The injectable collagen scaffold is placed under ultrasound guidance and supports the body's own repair processes through acellular matrix-induced chondrogenesis — recruiting the patient's progenitor cells rather than delivering external cells or tissue.

Moderate-to-advanced OA (KL III–IV): a dual-injection protocol combining ChondroFiller injection with Arthrosamid may be recommended. The two products address different problems in the same joint. ChondroFiller injection is the regenerative scaffold component; Arthrosamid is a separate, non-regenerative polyacrylamide hydrogel used for joint cushioning. They work through different mechanisms and are not a single blended treatment.

Extreme end-stage presentations: a Tri-Active combination — ChondroFiller injection, Arthrosamid, and autologous mesenchymal stem cells (MSCs) — may be considered to address structural, mechanical, and cellular demands simultaneously.

This tiered model replaces the binary suitable/not-suitable verdict found in surgical cartilage repair trials. OA grade is a routing variable, not a ceiling.

Joint alignment — why mechanics must be stable first

Stable joint mechanics are the one structural factor the assessment team weighs most carefully before proceeding with ChondroFiller injection. The collagen scaffold recruits the patient's own progenitor cells and matures over time — a process that depends on a mechanically sound environment. Without it, the forces acting on the treated surface can disrupt the scaffold before repair is established.

Untreated coronal malalignment, active ligament instability, and meniscal deficits that are directly driving wear are each assessed on this basis. Where any of these is identified, the clinical team determines whether correction can be arranged prior to or concurrent with the ChondroFiller injection — making malalignment a modifiable factor rather than a permanent barrier to treatment. The evidence base does not specify a universal varus or valgus degree threshold that triggers deferral rather than concurrent correction; how much deformity is present, and what correction is feasible, is a clinical judgement made at assessment.

Patients who have already had ligament reconstruction or meniscal repair are not excluded on those grounds. Provided the joint is now structurally stable following that surgery, the prior procedure is a neutral or even positive indicator — the structural environment has already been addressed. The distinction is between an unstable joint that remains untreated and a repaired one that has since been stabilised.

Prior treatments — what your surgical or injection history means

Previous surgery on the affected joint — whether meniscal repair, ligament reconstruction, or treatment for osteochondritis dissecans (OCD) — is generally read as a positive contextual indicator at ChondroFiller injection assessment, not a reason for concern. What matters is the structural condition of the joint after that surgery, not the fact that it took place. If the repair has stabilised the joint, the mechanical environment ChondroFiller injection requires is already in place.

Patients who have previously undergone microfracture are not automatically excluded. This distinguishes ChondroFiller injection from many surgical cartilage repair trials, which routinely disqualify revision cases; no such revision-exclusion rule applies here, making the pathway accessible to a broader group.

Prior injection history — hyaluronic acid, PRP, or corticosteroid — does not disqualify a patient from assessment either. Each of those treatments works through a different mechanism and at a different stage of the joint-health pathway, and their use does not affect ChondroFiller injection candidacy.

The single mandatory deferral is active infection, whether localised to the joint or systemic. ChondroFiller injection is not administered until infection has been fully treated and the patient has been formally reassessed. The deferral is temporary: clearance, confirmed at review, reopens the assessment pathway.

Getting a formal assessment at the London Cartilage Clinic

The assessment at the London Cartilage Clinic brings together imaging review, physical examination, and clinical history to determine which protocol tier fits each patient — not to produce a binary accept or decline. MRI confirms the nature and depth of cartilage damage; weight-bearing X-rays allow Kellgren-Lawrence grading of joint space; and clinical examination tests alignment and ligamentous stability in the same appointment. Symptom duration, functional impact, and prior treatment history complete the picture. The four filters — defect extent, OA grade, joint alignment, and treatment background — are evaluated together, and the outcome is a personalised protocol recommendation rather than a pass-or-fail verdict.

Liquid Cartilage™ is delivered in the UK at the London Cartilage Clinic on Harley Street, the UK's certified centre for ChondroFiller injection. Book an assessment via londoncartilage.com.