What a cartilage grade on your scan report actually means

Receiving a scan report that mentions "Grade 2" or "Grade 3" cartilage change can feel alarming — but the grade is a structural description, not a forecast for your joint. It tells a clinician how far into the cartilage layer the damage reaches, not how much pain you are having or whether surgery is inevitable.

That distinction matters. Two patients with identical grades can have very different day-to-day experiences; equally, some people with significant structural change remain largely symptom-free. The scan is read alongside your symptoms and clinical history, not in isolation.

Grade also works alongside defect surface area — how wide the damaged zone is, measured in square centimetres — and your activity demands. These three factors together form the basis for treatment planning; no single number from a report settles the question on its own. A specialist assessment is what converts scan measurements into a clinical recommendation.

The sections below map each cartilage grade to the anatomy it describes and the pathways typically considered at that stage.

The ICRS grading scale: Grades 1 to 4 explained

Four grades define the ICRS system, each anchored to a specific depth of tissue loss within the cartilage layer.

Grade 1 marks the earliest structural change: the surface is softened or shows superficial fissuring, but the overall thickness of the cartilage is preserved. Under the Outerbridge classification — the predecessor system widely used in both arthroscopic and MRI reporting — this corresponds to Grade I. Clinicians and radiologists may use either system; the criteria map closely enough that they are treated as interchangeable in most clinical settings.

Grade 2 means partial-thickness loss involving less than 50% of the cartilage depth. The damage extends into the middle layers but does not yet reach the deeper zone approaching bone. Think of it as the cartilage being worn partway down rather than thinned through.

Grade 3 is the most clinically consequential tier because it is where most treatment-pathway decisions branch. Loss extends beyond 50% of cartilage depth, and the grade is further divided into four subgrades that track exactly how far toward — but not yet through — the subchondral bone the damage reaches: 3A sits above the calcified cartilage layer; 3B reaches the calcified layer; 3C penetrates it without breaching the subchondral bone beneath; 3D describes surface blistering over an underlying lesion of greater-than-50% depth. The distinction matters because it signals how much structural support remains between the defect and the bone.

Grade 4 is full-thickness loss: cartilage is gone and subchondral bone is exposed. This is the deepest category in the classification and the one most likely to require surgical assessment, particularly if the exposed area is wide.

Across all four grades, depth is only part of the picture — surface area and joint location remain co-determinants of what comes next, as set out in the sections that follow.

Why the shoulder's thin cartilage makes grading more demanding

Shoulder articular cartilage is notably thin — the humeral head carries roughly 1 to 2 mm, while the glenoid surface measures less than 1 mm, comparable in scale to the edge of a fingernail. For context, knee cartilage in the medial compartment can reach 4 to 6 mm. At shoulder depths, half a millimetre separates one subgrade from the next.

At a standard 1.5 Tesla field strength, resolving that distinction reliably is difficult. Differentiating Grade 3A from Grade 3C on a routine shoulder MRI sequence — where the signal from a sub-millimetre sliver of calcified cartilage must be distinguished from adjacent tissue — requires imaging conditions that a standard protocol may not provide. Three Tesla (3T) MRI with a dedicated surface coil is generally required to achieve the spatial resolution needed for accurate grading in this joint; it is not an upgraded option but the appropriate baseline for this anatomy.

The glenoid surface compounds the challenge further. Its extreme thinness and the complex geometry of the glenohumeral joint mean that focal lesions here are particularly easy to miss or under-characterise on lower-resolution scans.

Patients who report significant pain but whose report returns a 'normal' or low-grade finding may have had a technically insufficient scan. A specialist review of the images — not only the written radiology report — can identify lesions or subgrade distinctions that a standard read misses, and may change the clinical pathway that follows.

Defect size: the second axis that shapes treatment choice

Alongside depth, the other number that shapes every treatment conversation is lesion area — measured in square centimetres on MRI as the surface footprint of the damaged zone.

Three broad bands capture how area influences clinical thinking:

• Under roughly 2 cm² — small, contained focal defects — are the best candidates for conservative and minimally invasive approaches, including injectable scaffold treatments such as ChondroFiller injection. There is enough surrounding healthy cartilage to support a scaffold as new tissue forms.
• Between approximately 2 and 4 cm², treatment choice becomes more nuanced. Microfracture, osteochondral autograft transfer (mosaicplasty), and cell-based repair are all considered, with the final selection depending on grade, location, and individual patient factors.
• Above roughly 4 cm², or where damage is multi-focal rather than discrete, surgical reconstruction is more likely to be required. Diffuse involvement across the glenohumeral joint may bring arthroplasty into the conversation.

Area and grade interact in both directions: a small but deep lesion and a large but shallower one can point toward quite different treatments even when their grade numbers look similar.

One important caveat applies across all three bands: the thresholds derive primarily from knee trials. The SUMMIT trial — which found MACI to be superior to microfracture for defects of 3 cm² or larger — studied the knee, not the shoulder. No equivalent shoulder-specific head-to-head data exist, so these numbers serve as a working clinical framework rather than a fixed rule, and individual assessment remains essential to determine which band applies and what it means for a particular patient.

Treatment pathways by grade and defect size

Cartilage repair practice organises shoulder management around four sequential goals — preserve, repair, regenerate, replace — with the appropriate tier determined by grade and lesion area working together.

Grades 1 and 2: preservation

Small, contained defects at these grades sit within intact cartilage margins and are well suited to a preservation-first approach. Physiotherapy and activity modification form the foundation. Where the biological environment needs support, orthobiologic injections — platelet-rich plasma (PRP) or bone marrow aspirate concentrate (BMAC) — may reduce inflammation and promote tissue health. For focal contained lesions, an injectable collagen scaffold such as ChondroFiller injection provides a further option: delivered as an ultrasound-guided outpatient procedure, the scaffold gels within the defect and supports matrix-induced chondrogenesis, recruiting the patient's own progenitor cells to produce new tissue. Suitability is confirmed on imaging review and physical examination, not on the severity of symptoms alone.

Grade 3: repair and regeneration

Once depth exceeds half the cartilage thickness and the lesion area approaches or exceeds 2 cm², management moves toward operative repair. Marrow stimulation (microfracture) is an established first-line surgical option for smaller defects. For appropriate defect sizes, osteochondral autograft transfer — mosaicplasty — has shown superior long-term clinical scores compared with microfracture alone. Larger Grade 3 lesions may require cell-based approaches such as ACI, MACI, or NanoACi. The treatment area thresholds applied here are largely extrapolated from knee trial data, as shoulder-specific head-to-head outcome evidence remains limited.

Grade 4: reconstruction and replacement

Full-thickness loss with exposed subchondral bone requires surgical reconstruction. Osteochondral autograft, osteochondral allograft, or cell-based repair (ACI/MACI) are the principal options for isolated focal Grade 4 findings. Total or hemi-shoulder arthroplasty is reserved for diffuse disease or when earlier repair has failed; it is not the default response to a single focal lesion.

For patients who have had focal cartilage repair — a materially different population from those requiring reconstruction or arthroplasty — return to full activity broadly follows a six-month horizon, with ballistic or high-load sport requiring longer. Progress is criteria-based: functional testing, symmetry, and graded load reintroduction take precedence over a fixed date.

Across all tiers, grade and area determine eligibility; the final decision also weighs patient age, activity level, associated joint pathology, and prior treatment history.

Getting the right assessment in London

Translating a scan report into a treatment decision requires more than reading the grade — it requires integrating it with how the joint actually moves, where symptoms localise, and what the patient needs to return to. That clinical synthesis is what a specialist assessment delivers, and it cannot be replicated from a report alone.

In practice, an initial consultation at this level covers three things: a structured clinical examination of shoulder biomechanics and provocation patterns; a detailed review of existing imaging, with repeat 3T MRI requested where the current scan is insufficient resolution for the glenoid surface; and a frank conversation about which pathway — preservation, repair, regeneration, or reconstruction — fits the defect characteristics established in earlier sections alongside the patient's activity goals and timeline.

For patients whose imaging shows a focal, contained lesion that may be suitable for a ChondroFiller injection, the precision of placement is a direct determinant of outcome. Professor Paul Y. F. Lee, who leads Liquid Cartilage™ delivery in the UK, performs assessments and procedures at the London Cartilage Clinic on Harley Street — an ICRS Teaching Centre of Excellence and the UK's certified delivery centre for the treatment.

Appointments can be arranged at londoncartilage.com.

1. [1] Articular cartilage repair. https://en.wikipedia.org/?curid=19042351 https://en.wikipedia.org/?curid=19042351
2. [2] Hyaline cartilage. https://en.wikipedia.org/?curid=1130627 https://en.wikipedia.org/?curid=1130627