The short answer on eligibility

Three conditions need to be met for a hip cartilage defect to qualify for ChondroFiller. The lesion must be classified as ICRS Grade III or IV — meaning the damage extends more than halfway through the cartilage layer or reaches the bone beneath. It must be focal and isolated, no larger than 6 cm², with healthy cartilage still intact around its edges to hold the injected scaffold in place. And the hip joint as a whole must not show significant background wear: patients whose overall joint health falls within Tönnis Grade 0 or 1 tend to be the strongest candidates.

Diffuse osteoarthritis affecting the whole joint does not meet these criteria. ChondroFiller is designed for a discrete, well-contained gap in otherwise viable cartilage — not for widespread, pan-articular degeneration.

Size, grade, containment geometry, and background joint condition all feed into that eligibility decision. Confirming whether a specific defect falls within these parameters requires MRI and a clinical assessment — imaging alone rarely tells the whole story.

What ICRS Grade III and IV actually mean

Cartilage damage in the hip is graded by depth, not by pain level alone — and that distinction matters when interpreting an MRI or arthroscopy report.

Imagine the cartilage surface as a road. A Grade I or early Grade II lesion is a scuff or shallow crack: the surface is disrupted, but most of the material beneath it remains sound. These changes sit below ChondroFiller's treatment threshold because the scaffold needs a structurally significant void into which the patient's own progenitor cells can migrate. Minor surface damage does not create that environment.

Grade III is where the depth criterion is met. The lesion extends more than 50% of the way through the cartilage layer — a deep pothole that has eaten through most of the road surface but has not yet broken through to the base beneath.

Grade IV means the full thickness of cartilage has been lost, exposing the subchondral bone below. That level of damage sounds severe, and it is — but it does not automatically indicate joint replacement. When the lesion remains focal and the surrounding joint is in reasonable condition (Tönnis 0 or 1), a scaffold-based injectable pathway remains a viable preservation option.

One point worth noting: symptoms and structural grade do not always align. A patient may experience significant hip pain at Grade II without meeting the depth criterion, while another may have a Grade IV lesion with comparatively manageable discomfort. Structural grading, typically confirmed on 3T MRI with arthroscopic assessment adding precision where needed, is what determines eligibility — not pain score alone.

Defect size, geometry, and the 6 cm² boundary

Size matters, but shape matters just as much — and that pairing is what the 6 cm² ceiling really means in practice.

The CE-mark upper boundary for a single ChondroFiller treatment is 6 cm². Lesions exceeding that fall outside the indicated range. In clinical practice, however, the sweet spot sits considerably lower: the ideal single defect is 1.0–3.0 cm², with a practical diameter of no more than roughly 2.5 cm. That diameter figure is useful for patients who have been given a measurement at imaging — it translates the area number into a rough physical size most people can visualise.

Below approximately 2–4 cm², microfracture remains a reasonable option for many patients. Where a defect approaches or exceeds 3 cm², the injectable collagen scaffold pathway tends to offer better results — and in the overlap zone around 2–3 cm², containment geometry often becomes the deciding factor. A well-bordered defect with stable surrounding cartilage is a stronger ChondroFiller candidate than a similarly sized lesion with irregular or confluent edges, because the scaffold needs walls to hold it in place; without containment, the hydrogel cannot be reliably retained within the defect.

Uncontained or confluent lesions represent a functional contraindication regardless of measured area. Where multiple smaller defects are present, suitability depends on the overall joint picture and their individual geometry — a question that imaging review and clinical assessment together are best placed to answer.

The hip-specific check: background joint health and Tönnis grading

Qualifying on grade and size is necessary — but not sufficient. The hip demands one further check that does not apply in the same way to other joints: an assessment of the overall cartilage environment surrounding the focal defect, classified using the Tönnis grading system.

Tönnis grading, derived from weight-bearing hip X-ray and cross-referenced with MRI findings, rates the degree of generalised osteoarthritis in the hip joint as a whole — separate from the focal lesion itself. Tönnis Grades 0 and 1 indicate minimal to no background OA, meaning the cartilage around the defect is largely intact. That surrounding tissue is what the repair process depends on: the scaffold recruits progenitor cells from the local joint environment, so if that environment is reasonably healthy, conditions for endogenous healing are far more favourable.

A useful analogy: a patch adheres reliably when the surface around it is sound. If the surrounding material has itself degraded, the patch has nothing stable to bond to.

Tönnis Grades 2 and 3 — moderate to severe generalised OA — indicate a joint environment too compromised to support structural repair. The Mazek 2021 surgical cohort specifically excluded Tönnis 2–3 patients on this basis. That does not mean there are no management options at this stage; it means the goal shifts from structural defect repair towards symptom management and joint-function support. The two aims call for different clinical conversations.

The most common hip lesion: FAI and why the cause must be addressed

The most common focal defect pattern that qualifies for ChondroFiller in the hip occurs on the anterosuperior acetabular surface — the leading edge of the hip socket. In younger, active patients, this damage is typically driven by cam-type femoroacetabular impingement (FAI): an abnormal bony prominence on the femoral head that catches against the acetabular rim during hip flexion, progressively stripping cartilage from that leading edge with each repetition.

Understanding the mechanism matters, because treating the cartilage defect alone is not sufficient when FAI is the underlying cause. If the bony prominence responsible for the damage remains in place, it will continue to impinge against the repaired tissue — working against the scaffold and, in time, re-creating the same injury.

Bony correction in cam-type FAI typically involves reshaping that prominent area of the femoral head. This step addresses the structural cause of the damage; ChondroFiller addresses the resulting cartilage defect. The two elements are complementary — neither alone resolves both problems. Bony correction is planned as part of the overall hip preservation pathway, separately from the injectable scaffold appointment itself, and the timing and method depend on the individual's anatomy, symptoms, and clinical picture.

Per the Perez-Carro 2021 cohort study (PMC8322278), ChondroFiller has been used successfully for full-thickness acetabular defects of this type, with early outcomes described as promising in treated patients.

Where ChondroFiller fits among other cartilage options

Three treatment approaches divide the focal cartilage repair landscape by defect size, and where a lesion sits on that scale is one of the clearest signals guiding which option a hip specialist is likely to recommend.

Microfracture is suited to smaller defects, typically below 2–4 cm². It is technically straightforward and widely available, but the tissue it produces is fibrocartilage — mechanically softer and less durable than native hyaline cartilage, which limits its long-term performance in an active hip.

At the other end of the scale, autologous chondrocyte implantation (ACI) and its membrane-based variant MACI are generally reserved for larger or previously treated defects above roughly 2–4 cm². Both are two-stage procedures: cells must first be harvested, cultured in a laboratory over several weeks, then reimplanted in a second operation. That timeline and complexity are appropriate for the largest or most demanding lesions, but they represent a significant commitment.

ChondroFiller occupies the space between these two options — above the microfracture ceiling, below the ACI/MACI entry point — and is delivered as a single outpatient appointment under ultrasound guidance, without cell harvest or a second procedure.

Published cohort data indicate that approximately 70–85% of treated patients achieve meaningful symptom relief, with hip function scores improving by roughly 30 points (mHHS) and MOCART 2.0 scores of 81–84 indicating good defect fill and scaffold integration. These are cohort-level findings rather than long-term randomised trial data, and outcomes should be understood as promising rather than definitive — a distinction that a pre-treatment consultation can address in relation to any individual's specific lesion.