What a focal hip cartilage defect actually is

A scan report showing a 'cartilage defect' is not the same as an arthritis diagnosis — and that distinction drives everything that follows.

Osteoarthritis involves progressive, diffuse thinning of cartilage across a large portion of the joint. A focal chondral defect is different: a discrete, bounded area of damage confined to one region of the femoral head or the acetabular socket, while the surrounding cartilage may remain largely intact. Because the problem is localised rather than widespread, the joint still has structural integrity worth preserving — and that is what keeps regenerative and joint-preserving treatment on the table. Left unmanaged, however, a focal defect can enlarge and trigger the very degenerative cascade it initially stood apart from.

The anatomy of the hip makes early identification both important and difficult. Articular cartilage here is typically only 1–2 mm thick and draped over a curved, ball-and-socket surface — physically thinner and more geometrically complex than cartilage in the knee. Even minor damage can be easy to miss on a standard scan, which is why the imaging pathway used to stage a defect matters as much as identifying that one exists.

How cartilage damage is graded and why depth matters

The grade assigned to a cartilage defect is not simply a label — it is a direct signal about what the tissue can and cannot do on its own, and what kind of intervention is likely to be needed.

The ICRS scale runs from Grade 1 to Grade 4:

• Grade 1 — surface softening. The cartilage layer is intact but has lost some of its normal stiffness. At this stage, conservative management — load modification, physiotherapy, and in some cases a biologic injection — is typically sufficient.
• Grade 2 — partial-thickness loss. Damage extends into the cartilage but involves less than half its depth. The structural layer is still present, and reparative options remain wide open.
• Grade 3 — deep partial-thickness loss. The defect has penetrated more than 50% of the cartilage depth, approaching or reaching the calcified layer immediately above the bone. There are four sub-types (A to D) that reflect exactly how close to — or through — that calcified layer the damage runs, but the clinically significant marker for most patients is simply the 50% threshold: this is the depth at which conservative management alone tends to be insufficient and a reparative or biologic intervention becomes the norm.
• Grade 4 — full-thickness loss. Cartilage is gone entirely, and the underlying subchondral bone is exposed. This shifts the treatment calculus meaningfully: the joint can no longer rely on remaining cartilage tissue for repair, so reconstructive or biologic restoration becomes the focus rather than symptom management alone.

Grades 3 and 4 are the point at which the conversation changes. Neither grade is automatically a path to joint replacement, but both call for a structured treatment plan beyond conservative care. Confirming which grade applies — and mapping the exact dimensions of the defect — is the work of specialist imaging, covered in the next section.

What imaging finds and where it falls short

Most patients arrive at a specialist consultation having already had an MRI — and many are surprised to be referred for further imaging. The reason is specific to how the hip conceals cartilage damage.

The sequence follows a logical clinical order. Weight-bearing X-rays come first: by loading the joint as it is in daily life, they reveal joint-space narrowing and allow the radiologist to assign a Tönnis grade for background osteoarthritis. That grade matters because it gates candidacy for joint-preserving procedures — significant pre-existing OA can close off reparative options before defect depth or size is even considered.

Standard MRI follows, but it carries a documented limitation: preoperative scans consistently underestimate actual defect size when compared with direct arthroscopic measurement, which has real consequences for surgical planning and technique selection. For subtle Grade 1 or Grade 2 lesions, even a 3-Tesla scanner with specialist sequences may miss the finding entirely — the curved ball-and-socket geometry makes thin surface damage genuinely difficult to resolve.

MR arthrography (MRA) addresses much of this. Gadolinium contrast is injected directly into the joint, and the hip is placed under gentle traction to open the joint space, improving visualisation of the cartilage surfaces. In hip preservation surgery patients, traction MRA detects femoral cartilage damage with a sensitivity of 89–95%, making it the gold-standard non-invasive modality for definitive staging.

One specific marker is worth noting: the 'Windshield Wiper Sign', visible on plain radiographs and MRI, identifies instability-related osteochondral lesions on the anterolateral femoral head. When present, it changes the treatment route — indicating that a periacetabular osteotomy may be required alongside any cartilage procedure, rather than arthroscopy alone.

Across all modalities, a structural finding on imaging is not a treatment mandate. Defect dimensions tell one part of the story; pain intensity, functional limitation, and clinical examination are needed to complete it.

How lesion size and location shape treatment decisions

Once a defect has been graded and sized on imaging, area in cm² becomes the principal fork in the treatment algorithm — more so, in practice, than grade alone.

Small defects (≤1.5–2 cm²) are generally the most treatable tier. At this size, conservative management or marrow stimulation (microfracture) is the standard starting point, and outcomes are strengthened considerably by augmenting the marrow clot with a collagen-based scaffold. For some patients in this tier, an ultrasound-guided injectable collagen scaffold — such as ChondroFiller injection, delivered as an outpatient procedure — can serve this augmentation role without the need for an operating theatre, providing a matrix for the patient's own progenitor cells to populate.

The 2–4 cm² range is genuinely contested territory. Both mosaicplasty and matrix-assisted cartilage implantation (MACI) have a place here, and the choice involves surgeon judgement applied to scan findings, joint access, and patient factors. The SUMMIT trial found that defects of 3 cm² or larger had significantly better pain and function scores at both two and five years when treated with MACI rather than microfracture alone — evidence that tilts technique selection toward cell-based approaches as lesion area increases through this range.

Defects larger than 4 cm² typically exceed what augmented microfracture or mosaicplasty can reliably address. ACI or MACI, or in some cases a fresh osteochondral allograft, become the realistic options.

Containment: the factor that overrides size

Defect area is not the whole story. For acetabular lesions specifically, containment — whether the lesion edges are bounded by intact cartilage and labrum — determines whether any scaffold material can physically be retained in the defect. Where the rim is disrupted, gracilis tendon allograft reconstruction of the labrum may be required first to re-create a contained cavity before a reparative technique can be applied. An uncontained defect treated without this step risks early displacement of whatever repair material is placed.

Who is most likely to benefit from joint-preserving treatment

Candidates for joint-preserving hip cartilage treatment share a recognisable profile across techniques, and knowing the typical criteria helps patients judge whether specialist input is the right next step.

Age below 50 is the most consistent selection marker across all repair approaches. Younger patients retain stronger biological capacity for tissue regeneration and sit further from the age range where joint replacement becomes the primary consideration.

Tönnis grade below 2 on weight-bearing X-ray is a structural prerequisite. Established osteoarthritis — where joint-space narrowing and bony change are already evident — substantially reduces the likelihood that cartilage repair of any kind will hold or provide durable relief. Where Tönnis grade 2 or above is confirmed, the pathway more commonly moves toward joint management or replacement planning rather than preservation.

Concurrent FAI must be addressed at the same time as any cartilage repair. Leaving the impingement mechanics unresolved means a treated cartilage surface faces the same abnormal loading that originally caused the damage.

Healthy surrounding cartilage, adequate bone stock, and an active lifestyle complete the picture. Typical candidates are people aiming to return to sport or maintain physically demanding daily activity — not those already managing advanced degenerative change.

Not everyone with a Grade 3 or 4 lesion will meet all these criteria, and being outside them does not close off treatment — it redirects it toward a different, still viable pathway. A specialist assessment establishes which applies: it typically covers clinical history, a review of existing imaging, weight-bearing X-rays if not already taken, and in many cases an MRI arthrogram to stage the cartilage precisely.

Realistic outcomes and next steps

For patients with Grade IV chondromalacia treated with augmented microfracture, published data show that nearly 90% achieve a clinically meaningful improvement in pain and function at two years — a figure that holds only in well-selected candidates. Approximately 11% of patients in the same series progressed to total hip arthroplasty within that window; this belongs in any pre-treatment conversation, not buried in the small print. At five years, recreational athletes treated for full-thickness acetabular lesions reached functional recovery thresholds equivalent to matched controls who had no cartilage damage at all — a useful reference point for what a good outcome can realistically look like.

The evidence base is credible, but it carries real limits. Long-term comparative randomised trial data specific to the hip — rather than extrapolated from knee cohorts — remain sparse. Mid-term series are a reasonable working guide, not a settled verdict, and outcomes data should be read with that in mind.

Where this evidence matters most is in matching the right starting point to the right patient. For those with smaller, contained defects who meet the selection criteria covered earlier, the pathway does not always require an operating theatre. ChondroFiller injection, outlined in the treatment section above, is one available route at this tier — an outpatient procedure rather than a surgical one. Specialist assessments at the London Cartilage Clinic on Harley Street, the UK delivery centre for this approach, can be arranged through londoncartilage.com.

The concrete next step in any case is a structured specialist review: imaging findings, clinical history, and weight-bearing X-rays examined together. Grade, defect size, containment, and background joint health are the four variables that determine which pathway applies — and that determination cannot be made from a scan report alone.

1. [1] Femoral cartilage damage detected on traction MR arthrography in hip preservation surgery patients. (2021). https://doi.org/10.1093/jhps/hnab038 https://doi.org/10.1093/jhps/hnab038
2. [2] Labral Gracilis Tendon Allograft Reconstruction and Cartilage Regeneration Scaffold for an Uncontained Acetabular Cartilage Defect. (2017). https://doi.org/10.1016/j.eats.2017.01.005 https://doi.org/10.1016/j.eats.2017.01.005
3. [3] Preserving Hip Stability Yields Better Cartilage Repair With Microfracture Treatment. (2025). https://doi.org/10.1016/j.asmr.2025.101284 https://doi.org/10.1016/j.asmr.2025.101284
4. [4] The Hip 'Windshield Wiper Sign': Osteochondral Defect of the Anterolateral Femoral Head. (2024). https://doi.org/10.1016/j.arthro.2024.06.003 https://doi.org/10.1016/j.arthro.2024.06.003
5. [5] Return to Sport After Hip Arthroscopy With Full-Thickness Acetabular Chondral Defect Treated With Microfracture. (2025). https://doi.org/10.1177/03635465251381784 https://doi.org/10.1177/03635465251381784
6. [6] Rates of Achieving Meaningful Outcomes 2-Year After Microfracture Augmented with Allograft Cartilage and Autologous PRP for Hip Chondral Defects. (2025). https://doi.org/10.1093/jhps/hnaf011.072 https://doi.org/10.1093/jhps/hnaf011.072