What a cartilage MRI report actually tells you

Receiving an MRI report before your clinic appointment is increasingly common, and making sense of it is a reasonable thing to want. The difficulty is that a radiology report describes what the scanner saw — signal characteristics, tissue boundaries, apparent depth of change — not what those findings mean for your knee specifically, or what, if anything, should be done about them.

Two terms worth spotting immediately: if your report refers to MOAKS (MRI Osteoarthritis Knee Score) or WORMS, it is using a whole-joint osteoarthritis staging framework, developed for research and OA surveillance. That is a different clinical picture from a report centred on a discrete, focal cartilage defect. Both may describe cartilage damage, but the language, the grading scales, and the treatment pathways they feed into are not the same.

For a focal defect report, four parameters carry most of the practical weight: depth grade, surface area, subchondral bone status, and lesion location. The sections that follow explain each in plain terms. The aim is to help you arrive at your consultation able to ask the right questions — not to substitute for the specialist review, imaging, and clinical examination that any treatment decision will still require.

The MRI sequences behind your cartilage report

Somewhere near the top of your MRI report, you may find a list of sequences — names such as PD FS, DESS, or T2 map. These are not different scans of different parts of your knee; they are different measurement modes run during the same session, each calibrated to reveal a particular tissue property.

The sequences most reports rely on are morphological ones — proton-density fat-saturated (PD FS) and three-dimensional DESS (double-echo steady-state) being the most common. Think of these as the scanner measuring shape: depth of any defect, surface contour, and how the signal looks compared to healthy cartilage beside it. A standard morphological report is sufficient for most initial clinical decisions, and MRI of this type is the gold standard for detecting focal cartilage problems; plain X-ray and CT contribute mainly in severe or advanced cases, or when surgical planning requires bone geometry data.

High-resolution 3D DESS in particular can now achieve sub-millimetre spatial resolution, which improves how accurately a lesion's boundaries and depth can be read — though the most advanced implementations (such as 7 Tesla scanners combined with deep-learning reconstruction) remain confined to specialist research centres.

Compositional sequences — T2 mapping, T1 rho (T1ρ), and dGEMRIC (delayed gadolinium-enhanced MRI of cartilage) — go a step further. Rather than mapping shape, they probe the biochemical fabric of the cartilage: proteoglycan content and collagen organisation. The analogy is the difference between noting a pothole (morphological) and testing whether the surrounding road surface is beginning to crumble (compositional). These sequences appear on research or specialist protocols; their absence from a routine NHS or private report is normal, not a shortfall in your care.

What the depth grade on your report means

The depth grade is usually the first number that catches the eye on a cartilage MRI report. In UK clinical practice it is most commonly expressed using the ICRS scale (International Cartilage Repair Society) — a four-step system originally developed for arthroscopic assessment that has since become standard shorthand on MRI reports.

The four grades, briefly:

• Grade 1 — Surface intact; a change in the MRI signal suggests early softening within the tissue but no visible thinning.
• Grade 2 — Partial-thickness loss involving less than 50% of cartilage depth. The surface is disrupted, but more than half the thickness remains.
• Grade 3 — Loss exceeding 50% of depth. Sub-grades 3A to 3D describe how far down the damage reaches: 3A stops above the calcified cartilage layer that anchors cartilage to bone; 3B reaches that layer; 3C passes through it but stops short of subchondral bone. Grade 3D is distinct in pattern — a blistered or delaminated surface overlying deep damage — and carries its own prognostic implications.
• Grade 4 — Full-thickness defect, with subchondral bone exposed at the base of the crater.

The 3A–3D sub-grades rarely appear explained on routine reports, yet they bear on which repair strategy, if any, is appropriate — making them worth raising explicitly at your appointment.

A practical caveat: studies measuring ICRS agreement between different readers have found only poor-to-moderate reliability, meaning the same lesion can attract different grades from different assessors. Treat the grade as useful orientation rather than a fixed measurement, and bear in mind that the treating clinician needs to review the actual image sequences — not the report summary alone — before drawing firm conclusions.

Some specialist-centre reports also reference an AMADEUS score, an MRI-native system designed specifically for untreated focal defects that shows moderate correlation with ICRS grading. Its presence signals a more granular assessment of what the images show; ask your consultant to translate the specific sub-scores into plain terms relevant to your situation.

Why lesion size often matters more than the grade

Grade alone does not determine treatment. Two patients can each carry a Grade 3 finding on their report, yet face entirely different clinical conversations — because one defect measures 1.5 cm² and the other 4 cm². Surface area, expressed in square centimetres, is arguably the more treatment-determinative figure on a cartilage MRI report, yet it is frequently absent as a number, replaced by descriptors such as 'small', 'moderate', or 'significant'.

Clinicians work with a practical size boundary that sits somewhere between 2 and 4 cm². Below that range, procedures that stimulate the bone marrow or transfer small plugs of bone and cartilage from elsewhere in the joint are generally considered proportionate. Above it, cell-based approaches — which culture the patient's own cartilage cells before reimplantation — tend to become the preferred option. The boundary is a clinical zone, not a hard line, and other factors (bone involvement, location, alignment) shift it in either direction.

The SUMMIT trial gives the 3 cm² threshold its sharpest clinical definition. In that study, patients with cartilage injuries of 3 cm² or more achieved meaningfully better KOOS pain and function scores with MACI (matrix-induced autologous chondrocyte implantation) compared with microfracture — a difference that held at both two and five years.

For smaller defects, size still matters. Evidence suggests that lesions exceeding roughly 1 cm in diameter may continue to enlarge over time if left untreated, carrying a longer-term risk of wider joint deterioration. This is not a reason to panic over a small finding, but it is a reason not to defer discussion indefinitely.

If your report does not state a measured area — only a prose description — that is a specific question worth raising with your consultant before any treatment pathway is agreed.

Four parameters that make a cartilage report actionable

Before your appointment, it is worth checking whether your report contains four specific items. Depth grade and lesion area — covered in the preceding sections — are two of them. The other two are less often explained to patients, yet they carry equal weight in determining what comes next.

Subchondral bone status. The subchondral bone is the layer of bone directly beneath the cartilage. Bone marrow oedema — inflammation within that bone — signals that damage extends beyond the cartilage itself and into the underlying structure. Subchondral cysts or a breach of the subchondral plate indicate more advanced involvement and materially affect both prognosis and the choice of repair technique.

Anatomical location. Where in the joint the defect sits changes its clinical meaning. The medial and lateral femoral condyles are weight-bearing surfaces; defects there are exposed to the full load of walking and running. The patellofemoral surface (the kneecap and the groove it moves in) loads differently and responds differently to repair. The tibial plateau presents its own biomechanical considerations. A report that says only 'medial compartment' without specifying the surface zone leaves part of the picture incomplete.

If any of the four parameters — grade, area, subchondral bone status, location — is absent from the written report, that is a precise question to raise before the consultation rather than during it. Knowing what to ask makes that conversation considerably more productive.

From report to consultation: what happens next

The written report captures what was visible on the scanner — but it cannot capture how your knee moves under load, how stable it feels in examination, or how your symptoms fit the imaging picture. These are the gaps a specialist appointment is designed to close.

A clinical review that goes beyond the report text typically adds three things: direct examination of the full image sequences rather than the radiologist's prose summary, a physical assessment of joint range of motion, stability, and patellar tracking, and, where appropriate, weight-bearing standing X-rays to evaluate alignment and the distribution of any joint-space narrowing. Expert review of the images themselves can also refine or, occasionally, revise an initial grade — the radiologist reading a screening scan and the specialist who has examined you may reach subtly different conclusions when looking at the same sequences together.

Arriving with the four parameters — depth grade, measured area, subchondral bone status, and anatomical location — clearly noted means the consultation can move quickly to the questions that matter: what the finding implies for your activity level, what a treatment pathway would involve, and what factors would change the recommendation in either direction.

For patients in London, specialist cartilage assessment combining image review, clinical examination, and standing X-ray evaluation is available at the London Cartilage Clinic on Harley Street (londoncartilage.com).

1. [1] Can the MRI based AMADEUS score accurately assess pre-surgery chondral defect severity according to the ICRS arthroscopic classification system?. (2022). https://doi.org/10.1186/s40634-022-00511-w https://doi.org/10.1186/s40634-022-00511-w
2. [2] Arthroscopic International Cartilage Repair Society Classification System Has Only Moderate Reliability in a Porcine Cartilage Repair Model. (2021). https://doi.org/10.1177/0363546521998006 https://doi.org/10.1177/0363546521998006
3. [3] Correlation of Arthroscopic Grading and Optical Coherence Tomography as Markers of Early Repair and Predictors of Later Healing Evident on MRI. (2023). https://doi.org/10.1177/19476035231154508 https://doi.org/10.1177/19476035231154508
4. [4] Hyaline cartilage. https://en.wikipedia.org/?curid=1130627 https://en.wikipedia.org/?curid=1130627