Two measurements that decide your hip treatment options

When a hip cartilage defect is found, two measurements shape the treatment conversation above everything else: how deep the damage goes, and how large an area it covers. These are not the same question, and answering only one of them leaves the picture incomplete.

Depth is recorded using the ICRS grading scale, which runs from Grade 1 (surface fissuring with no structural breach) through to Grade 4 (damage that has penetrated through the subchondral bone beneath the cartilage). Area is measured in square centimetres, typically confirmed on MRI. Both figures are needed before any treatment decision is made — whether that means a protective injection programme, a procedure to address structural contributors, a biological rebuild, or hip replacement.

This matters because symptoms alone are an unreliable guide. A patient with a small-area, low-grade lesion and a patient with a large-area Grade 4 defect can arrive in clinic reporting a similar level of hip pain and stiffness. Plain X-rays may not distinguish them clearly at early stages. MRI is the tool that resolves the picture — confirming ICRS grade, measuring defect size, and assessing the integrity of the bone beneath.

From those two figures — depth and area — a four-tier pathway follows: protect the joint and slow further wear; fix any structural problem driving the damage; rebuild cartilage tissue where the biology supports it; or replace the joint when preservation options are exhausted. Each tier is unlocked or closed by where a patient sits on those two axes, not by age, pain score, or how the hip looks on a plain radiograph.

Why hip cartilage cannot repair itself

Unlike bone or skin, the hyaline cartilage lining the femoral head and acetabulum has no blood supply and no nerve endings. Both absences carry direct clinical consequences. Without nerves, early cartilage damage produces no pain signal — a Grade 1 or early Grade 2 lesion can be present for years before causing any symptoms, discovered only incidentally on imaging. Without blood vessels, the body cannot mount the repair response it uses elsewhere; instead of regenerating true hyaline cartilage, damaged tissue is patched with fibrocartilage, a structurally weaker substitute prone to breakdown under the load demands of a hip joint.

This biological limitation is why the structural causes of focal hip cartilage damage deserve specific attention in younger adults. Femoroacetabular impingement (FAI) — where a bony abnormality of the femoral head or acetabulum generates abnormal contact forces against the acetabular cartilage — is among the most common drivers of focal chondral lesions in adults under 50. Hip dysplasia, in which the socket does not fully cover the femoral head, concentrates load across a smaller-than-normal surface area, accelerating graded wear. Both conditions are structural and addressable; focal lesions left without intervention tend to enlarge and deepen, progressively narrowing the window in which preservation procedures remain a realistic option.

ICRS grading: what defect depth means for your options

The ICRS scale gives depth a clinical language, translating what a surgeon sees on MRI into four grades that each carry different implications for what intervention — if any — is likely to be needed.

Grade 1 describes surface fissuring: a scratch on the cartilage face with no structural breach below. Grade 2 extends less than halfway through the cartilage layer — damage is present but the deeper architecture remains intact. At both these grades, protective strategies and symptom management take priority; formal cartilage repair is possible but often not yet warranted.

Grade 3 is where clinical decision-making typically shifts. Damage here extends beyond 50% of cartilage depth, with sub-grades (3A through 3D) reaching progressively closer to the subchondral bone beneath. This is the range in which active biological repair or regeneration is most commonly considered — the lesion is deep enough to behave unpredictably if left, but the subchondral bone may still be largely intact and supportive of a repair procedure.

Grade 4 marks full-thickness cartilage loss extending through to or involving the subchondral bone. The window for preservation surgery narrows here, but it does not close automatically. Defect area, the patient's age and activity level, and the condition of the underlying bone all feed into whether a repair or biological procedure remains realistic. Grade 4 opens a conversation about joint replacement — it does not end the conversation about preservation. No single grade should be read as a final verdict before those additional variables have been assessed.

Defect area and which repair techniques it rules in or out

Size — measured in cm² on MRI — is as clinically important as depth, and the two dimensions do not always point in the same direction. A small, deep defect and a large, shallow one require different solutions.

Smaller defects (approximately 1–2 cm²) are well suited to single-stage osteochondral autograft transfer — OATS, or mosaicplasty when multiple plugs are used. A small cylinder of bone-and-cartilage is taken from a lower-load area of the joint and transferred directly into the defect, placing true hyaline cartilage where native tissue has been lost. Donor-site discomfort from the harvest site is a meaningful consideration and forms part of any pre-operative discussion.

Larger defects (roughly 2–10 cm²) are where MACI has its strongest evidence base. The SUMMIT trial demonstrated that for defects of 3 cm² or more, MACI produced significantly better pain and function outcomes than microfracture at both two and five years. MACI is a two-stage procedure: cartilage cells are harvested, cultured in a laboratory, and re-implanted on a collagen membrane at a second operation.

Microfracture — marrow stimulation through the subchondral bone — has a declining role across the size range. The repair tissue it produces is the fibrocartilage substitute described in the previous section, prone to breakdown within two to three years. There is an additional structural concern: the procedure can damage the subchondral bone plate, making any subsequent repair more technically demanding.

For suitable focal defects, a ChondroFiller injection offers a minimally invasive outpatient option. An acellular collagen scaffold is delivered into the defect under ultrasound guidance, gels in situ, and provides a three-dimensional structure that the body's own repair cells can populate and remodel over time — no theatre, no general anaesthetic, no second-stage procedure. That practical difference from cell-based surgery is as relevant to many patients as the biological one. Most size-threshold evidence in cartilage repair originates from knee research; hip-specific data is developing, and imaging-led assessment determines individual suitability for any technique.

The four-stage pathway from protection to replacement

Knowing a lesion's grade and area opens the map — the four-stage pathway places a patient on that map and indicates which direction makes clinical sense.

Stage 1 — Protect applies where damage is early and the priority is buying time for further assessment. Physiotherapy, activity modification, and intra-articular injections form the toolkit: both corticosteroids and high-molecular-weight hyaluronic acid have randomised controlled trial evidence supporting symptom management in hip osteoarthritis.

Stage 2 — Fix addresses the mechanical environment. A cartilage repair carried out while femoroacetabular impingement or labral instability persists is building on unstable ground; the structural problem will re-damage any repair tissue that forms. Hip arthroscopy allows many of these corrections through small incisions, with shorter recovery than open surgery, and is most applicable before widespread joint degeneration has set in.

Stage 3 — Rebuild is where biological regeneration is assessed against what imaging actually shows. Options at this stage include injectable collagen scaffold treatment (ChondroFiller injection, delivered under ultrasound guidance as an outpatient procedure), single-stage surgical approaches such as OATS or AMIC, and cell-based implantation including MACI or ACI. No single ICRS grade or arthritis stage automatically removes a patient from consideration at this rung; examination and MRI findings determine individual suitability.

Stage 4 — Replace is reached when biological options have been exhausted or are not realistic given the extent of bone-on-bone disease. Total hip replacement reliably reduces pain and restores function; approximately 58% of replacements are estimated to remain functioning at 25 years. Even at this threshold, a combination biological review — pairing a regenerative scaffold with a joint-space filling injection — may be appropriate in selected patients before committing to surgery.

The pathway is a decision ladder, not a conveyor belt. Some patients enter at Stage 2 or 3 following an incidental imaging finding; others move back to an earlier rung once a structural problem has been corrected. Where a patient sits at first assessment is not necessarily where they will remain.

Why MRI is the decisive tool, not symptoms or X-rays

Plain radiographs remain useful — they identify joint space narrowing, bony erosion, and subchondral cysts — but they cannot visualise cartilage directly. A hip that appears near-normal on X-ray may already carry a Grade 3 chondral lesion across several square centimetres of the femoral head. That gap between what a plain film shows and what is structurally present is precisely where misclassification risk sits.

MRI resolves this. It is the reference standard for confirming ICRS grade, measuring defect area in cm², assessing subchondral bone integrity, and identifying co-pathologies — most commonly labral tears — that influence both treatment eligibility and surgical planning. A defect that seems clinically manageable may, on imaging, extend through the calcified cartilage layer into subchondral bone, shifting its grade and narrowing the techniques that remain applicable.

The consequence of bypassing MRI runs in both directions. A structurally significant Grade 3 defect in a patient who is still functioning reasonably well may be under-treated, closing the repair window before bone-on-bone disease sets in. Equally, a shallow Grade 1–2 lesion with limited structural significance may be over-treated when the clinical response is to pain levels rather than imaging findings. Neither error is trivial — one accelerates the path to replacement, the other diverts resources from patients with greater structural need.

For patients who cannot tolerate a standard-bore scanner, open MRI alternatives are available; weight-bearing MRI (MAI Motion) can add functional load data where the clinical picture warrants it. Whichever route is used, imaging-confirmed grade and defect area are what place a patient at the correct stage of the pathway — and determine which intervention, if any, is appropriate at that stage.

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