The short answer on candidacy

Most patients asking about ChondroFiller® injection want a direct answer to one question: am I likely to be a candidate? The short answer is that the injection pathway is designed for people with focal cartilage damage — a distinct, localised defect rather than widespread joint degeneration — and it carries no published upper age limit and no fixed ceiling on defect size.

The three principal lesion types suited to assessment are focal chondral lesions, osteochondral defects (OCD), and defects that have developed following meniscal injury. Crucially, joint mechanics need to be stable: untreated ligament instability or significant malalignment can undermine outcomes, and a specialist will consider both when reviewing your imaging.

Being described as 'bone on bone' on a plain X-ray does not automatically close the door. Clinical assessment weighs biology, defect morphology, and joint loading pattern alongside any imaging label — so whether the injection pathway is appropriate is a question for a formal consultation, not a self-screen.

The procedure itself is an ultrasound-guided outpatient injection, performed without general anaesthetic or surgical incision. If you have a focal cartilage defect and want to understand where you sit within that picture, the sections below set out the specific criteria in more detail.

What 'focal cartilage defect' means in practice

The distinction matters clinically. A focal cartilage defect is a bounded, localised crater — an area of cartilage loss within a joint where the surrounding tissue remains largely intact. On the ICRS grading scale, these defects typically sit at Grade 2 (affecting less than half of cartilage depth) or Grade 3 (extending beyond 50% of depth, with sub-grades reaching to the calcified layer). Grade 4, where loss runs through the subchondral bone across multiple joint compartments, describes a different clinical picture — closer to pan-articular degeneration than to the contained defect profile that the injection addresses.

ChondroFiller® works through acellular matrix-induced chondrogenesis. Once the collagen scaffold is placed within the defect, it recruits the patient's own progenitor cells — drawn from the surrounding synovium and subchondral bone — into the damaged zone. An ex vivo osteochondral model recorded a 2.4-fold increase in DNA content by day 14 compared with untreated defects, confirming this cell-migration mechanism. The scaffold promotes endogenous repair within the defect itself; it does not treat a joint surface that has deteriorated broadly across multiple compartments.

Published evidence spans three joints. A prospective hip cohort (n=26) examined acetabular lesions exceeding 2 cm²; a randomised multicentre study enrolled patients with small-to-medium focal knee defects; and a 2025 wrist study applied the scaffold to residual chondral defects of 0.5–2 mm depth following intra-articular fracture. In each case, the treated site was a discrete, bounded lesion rather than widespread degenerative change.

How MRI maps your defect before treatment

Before an injection is planned, a specialist will review MRI images of the affected joint. The scan reveals the defect's precise location, depth, and boundaries — detail that plain X-rays and clinical examination alone cannot provide. That information then drives the treatment plan directly.

One box of ChondroFiller® is standard for most presentations. Where imaging shows a larger lesion or defects spanning more than one compartment, two or three boxes may be prescribed. The scan helps the specialist plan exactly how much scaffold to place and where.

Precision here is clinically meaningful. A 2025 wrist study found that overfilling chondral defects with the scaffold led to fibrous tissue formation, whereas flush application — filling the defect to the level of the surrounding cartilage surface — did not. That distinction explains why accurate sizing from imaging matters, not simply as a planning formality but because the volume placed shapes the quality of the tissue response.

Defect morphology also matters: whether the lesion is well-contained and bounded influences both the dose and the expected repair process. MRI findings are reviewed alongside the full clinical picture during consultation — the scan is one essential input into candidacy, not a standalone decision tool.

Joint stability and alignment as candidacy factors

The scaffold needs a stable mechanical environment to work in. When a joint carries untreated ligament instability, abnormal kinematics generate shear forces across the repair site that can disrupt early tissue ingrowth. For this reason, unresolved ligament instability is listed as a relative contraindication to ChondroFiller® injection — as is significant malalignment, such as pronounced varus or valgus, which places asymmetric load on the treated compartment.

Neither factor is an automatic exclusion. Both are relative contraindications, meaning clinical judgement determines whether the joint's mechanical environment is compatible with scaffold regeneration in a given patient. Someone whose instability has been corrected surgically, or whose alignment is being managed through bracing or physiotherapy, may still be assessed as a candidate. Patients should not self-exclude on the basis of a previous ligament repair or a mild alignment concern.

There is a separate, practical loading consideration that follows on from the same mechanical logic. An in-vitro biomechanical study found that the ChondroFiller scaffold is initially soft and cannot fully protect the opposing cartilage surface under cyclic loading. A graduated post-injection loading protocol is therefore part of the clinical plan — not because the treatment is inherently fragile, but because giving the scaffold time to achieve stable defect filling improves the quality of the subsequent repair.

When advanced OA is the principal reason for exclusion

Published clinical outcome data provides the clearest indication of where the injection is unlikely to help. In a hip arthroscopy cohort followed over three to five years, patients who had pre-existing osteoarthritis graded Tönnis 2–3 — indicating moderate-to-severe joint-wide degeneration — showed poor results, in contrast to the 81% good or excellent outcomes recorded across the broader cohort. That distinction maps directly to mechanism: ChondroFiller® supports repair within a discrete, bounded defect by recruiting the patient's own cells into the collagen scaffold, but it cannot reverse degeneration spread across the whole joint surface.

The phrase 'bone on bone', commonly used by patients to describe their own condition, does not translate to a specific clinical grade. It is a colloquial description that may reflect end-stage pan-articular OA or, in some cases, a joint that still has focal areas of remaining cartilage alongside generalised narrowing. A specialist reviewing imaging and clinical history can distinguish between these presentations — and the London Cartilage Clinic notes explicitly that a 'bone on bone' appearance on plain radiograph does not automatically exclude someone from assessment.

Patients for whom this injection pathway is not appropriate are not without further options. Surgical cartilage restoration and, where appropriate, joint replacement remain established pathways, and a specialist assessment is the right starting point for understanding which route fits the individual joint and clinical picture.

What the candidacy assessment actually involves

Candidacy for ChondroFiller® injection is not determined by any single criterion. Specialists evaluate each case across four overlapping dimensions: the physics of the joint (mechanics, alignment, and loading pattern); the chemistry (the scaffold's local environment, including bone quality and prior injections); the patient's biology (age, regenerative capacity, and systemic health); and the timing of the defect (how long the damage has been present and whether the repair window is still open). These four lenses explain why no online self-screen tool, however well structured, can replace a consultation.

A formal assessment draws together MRI images, clinical history, prior treatment, and the specialist's direct evaluation of joint function. The weight given to each factor shifts depending on the joint, the defect, and the patient — which is why two people with superficially similar imaging findings may receive different recommendations.

Search MSK lists specialists across the UK who offer ChondroFiller injection. Use the region and specialty filters to find one who can review your imaging and clinical picture.