The ICRS scale at a glance

Your scan report or clinic letter may carry a phrase such as 'ICRS Grade 3B focal chondral defect, medial femoral condyle.' The International Cartilage Repair Society (ICRS) scale is simply a five-step depth chart — a shared language surgeons and radiologists use so that everyone reading the report knows exactly how far through the cartilage the damage goes.

| Grade | Plain description | What it means structurally | |-------|------------------|---------------------------| | 0 | Normal | Cartilage intact; surface smooth and firm | | 1 | Nearly normal | Surface softening or very shallow fissures; deeper layers unaffected | | 2 | Abnormal | Damage reaches less than half the cartilage thickness | | 3 | Severely abnormal | Damage extends more than halfway through, approaching but not breaching the bone beneath | | 4 | Severely abnormal | Full-thickness loss; underlying bone exposed |

Why the Grade 3 sub-divisions matter

Grade 3 is split into sub-grades A through D depending on the precise depth and character of the lesion — for example, whether it has reached the thin calcified layer just above the bone, or whether the surface shows a blister-like swelling (a 'blistering' pattern). To a patient these sub-labels may look like fine print, but to a surgeon planning repair they influence which technique is structurally feasible, so it is worth noting your letter if you have one.

Grade measures depth — not pain

One thing the scale does not measure is how much your knee hurts. Cartilage contains no nerve endings, so the depth of damage and the severity of symptoms can move quite independently of each other. That disconnect is worth holding in mind as you read further: a Grade 4 finding does not automatically mean a Grade 4 experience, and the histological evidence confirms these grades reflect genuine tissue loss rather than imaging artefact (correlation with laboratory scoring: r = 0.811). The practical implications of that pain–grade gap are explored in the next section.

Why a high grade doesn't always mean severe pain

Scan grades and symptom levels measure different things — and the gap between them is wider than most patients expect.

Cartilage tissue contains no nerve endings. Damage confined to the cartilage layer itself cannot be felt directly; pain tends to arise when load transfers onto the exposed subchondral bone beneath, or when the joint responds to injury with inflammation. This means a relatively shallow Grade 2 lesion sitting in a mechanically loaded spot can sometimes produce more discomfort than a larger full-thickness Grade 4 defect in a less-loaded area. The grade tells a surgeon how deep the damage goes — it does not transmit the experience of living with it.

This matters clinically. A 2026 cross-sectional study of 57 patients with MRI-confirmed focal chondral lesions found that WOMAC pain scores and functional scores were moderate and statistically comparable between Grade 3 and Grade 4 groups. In other words, symptom severity alone could not reliably distinguish between the two highest grades. The study is a single small sample, and larger work is needed to confirm the finding, but it supports what clinicians already observe day to day: pain is a real and important signal, yet it is not a dependable proxy for structural depth.

One clinical test did show a meaningful association with Grade 4 severity — McMurray's test, which was positive in 86% of Grade 4 cases versus 30% of Grade 3 cases. The likely explanation is not that deeper cartilage damage produces a distinct pattern of pain, but that Grade 4 lesions were far more often accompanied by meniscal tears (86% versus 30%). It is the meniscal co-pathology that drives the positive McMurray finding, not cartilage depth itself — a reminder that a high ICRS grade rarely exists in isolation.

For anyone processing a scan result: your pain is real, and the grade on your report is also real. They are simply measuring two separate things, which is why treatment planning draws on both — and why neither one alone is enough.

Why grade is only half the picture: size, anatomy, and patient factors

The grade on your scan report answers one question: how deep is the damage? Surgeons need at least two more answers before settling on a repair strategy — how wide is the defect, and what is the broader clinical picture of the person in front of them?

Defect area: the second axis of the decision

Surface area, measured in cm², runs alongside grade as a joint determinant of which technique is feasible. The approximate clinical thresholds sit around 2–3 cm² and ≥3 cm²: a Grade 3 defect of 1.5 cm² and a Grade 3 defect of 4 cm² may carry the same letter on a scan report yet follow very different treatment paths — microfracture or mosaicplasty for the smaller lesion, MACI or osteochondral allograft for the larger.

One practical caveat: MRI systematically underestimates defect size compared with direct arthroscopic measurement. The figure on a scan report is better read as a floor than a ceiling, which is one reason some treatment decisions can only be confirmed at formal assessment.

What else your assessment measures

Concomitant pathology — meniscal tears, ligament instability, malalignment, patellofemoral loading patterns — affects whether a repair is likely to hold over time. Patient factors carry equal weight in concrete ways: a patient over 45 with a higher BMI is often steered away from microfracture even for a small defect, because the marrow-derived cell quality it depends on tends to decline with age and metabolic load — and longer-term outcomes data reflect this. Activity level and symptom duration shift the calculus further still. Trial data rarely disaggregate all of these variables simultaneously, but no clinician ignores them — integrating them into a personalised recommendation is the purpose of specialist assessment.

Grade 1–2: the conservative pathway first

Grades 1 and 2 carry an important clinical message: the damage has not yet breached the halfway point of the cartilage layer, and the priority at this stage is active rehabilitation, not the operating list.

What conservative care actually involves

Physiotherapy is the backbone of Grade 1–2 management — and the focus is specific rather than generic. Quadriceps strengthening is central because the quadriceps absorbs load through the joint and, when weak, shifts mechanical stress directly onto the articular surface. Alongside this, activity modification and graduated load management protect the lesion from repetitive provocation while capacity is rebuilt. For patients carrying excess weight, even modest reduction meaningfully decreases the compressive forces the cartilage is being asked to tolerate on every step.

Injection support can run in parallel when inflammation or pain is limiting progress. Corticosteroid injections offer relatively fast symptom relief to create a window for rehabilitation to take hold. Hyaluronic acid (HA) and platelet-rich plasma (PRP) are used to support joint environment and function; evidence for PRP in early chondral damage is growing, though it is best discussed in terms of what it may do rather than what it guarantees.

For lower-grade focal defects — where the cartilage borders are largely intact — an injectable collagen scaffold such as ChondroFiller injection may also be considered. Delivered as an ultrasound-guided outpatient procedure, it works by placing a matrix into the defect that recruits the patient's own progenitor cells to support repair tissue formation. At Grade 1–2, where there is still healthy surrounding cartilage to build against, this sits as one option in the conversation rather than a last resort.

When escalation becomes appropriate

Conservative management deserves a genuine trial — typically around three to six months of structured physiotherapy, with injection support where indicated. Persistent pain and functional limitation beyond that window, despite adherence to the programme, is the primary escalation signal. A second indicator is imaging progression: if a follow-up scan shows the defect deepening or widening, waiting is no longer the lower-risk option. Either of these — sustained symptoms after an adequate conservative trial, or documented structural deterioration on imaging — warrants specialist reassessment to determine whether the pathway needs to change.

Grade 3–4: matching the repair to the defect

Once a defect reaches Grade 3 or 4, the treatment menu expands — but so does the role of defect size in steering the choice. Rather than a single recommended technique, what exists is a ladder of options matched roughly to three size bands.

Smaller defects (under ~2 cm²)

Arthroscopic debridement and chondroplasty — smoothing frayed cartilage edges — is the least invasive surgical step and reliably reduces mechanical catching or locking symptoms. It does not regenerate tissue, so it is best reserved for cases where mechanical symptom relief is the primary aim rather than structural repair.

Microfracture drills fine channels into the exposed subchondral bone to recruit marrow stromal cells, which then produce a fibrocartilage fill. It remains an option for lesions under roughly 2 cm², though its attractiveness has declined: a 15-to-17-year randomised study shows outcomes no better than debridement alone, alongside added risks of subchondral fracture and intralesional osteophyte formation.

Moderate defects (~2–3 cm²)

Mosaicplasty transfers osteochondral plugs from a low-load area of the same knee to fill the defect, implanting hyaline cartilage and bone in place of fibrocartilage. The same long-term randomised trial places mosaicplasty ahead of microfracture at this size range. Grade-4-specific randomised data are limited — most trials aggregate Grades 3 and 4 — but the 15-to-17-year comparative evidence favours mosaicplasty over microfracture, and published cohort data in higher-grade defects show meaningful functional improvements.

Larger defects (≥3 cm²) and beyond

For defects at or above 3 cm², matrix-associated autologous chondrocyte implantation (MACI) is the preferred biological reconstruction. The SUMMIT trial demonstrated significantly improved KOOS pain and function scores at two and five years compared with microfracture for lesions in this range. Where the defect is too large for autograft, osteochondral allograft — donor bone and cartilage — provides the necessary volume.

Across all these options, sub-grade-level evidence is limited; most published trials do not separate Grade 3 from Grade 4. A specialist will weigh defect size, border integrity, and patient factors together rather than applying a single algorithm.

For smaller focal lesions where healthy cartilage margins remain intact — as described in the previous section — an injectable scaffold such as ChondroFiller injection represents an earlier pathway option, delivered as an outpatient procedure rather than a theatre-based reconstruction.

Getting a specialist read on your grade

Reading through the options mapped in this article, patients often expect their ICRS grade to translate cleanly into a recommended treatment. In practice, it rarely does — and that is not a limitation of the grading system. It reflects the fact that depth of damage is one variable among several: how wide the defect runs, whether the cartilage borders are intact, what the patient's activity demands are, and whether the joint carries alignment or meniscal issues alongside the chondral lesion. Depth, size, and patient context together determine which technique is feasible — and which the evidence actually supports at that combination.

The grade is where the clinical conversation starts. A specialist assessment draws on the scan, a physical examination, and a direct discussion of what function and activity the patient wants to recover — and it is that combination which produces a realistic, individual pathway.

For patients in London exploring whether an image-guided injectable option — including a ChondroFiller injection — may be appropriate for their grade and defect, assessments are available at the London Cartilage Clinic on Harley Street, the UK delivery centre for Liquid Cartilage™. Book via londoncartilage.com.

1. [1] Arthroscopic-Assisted Mosaicplasty for ICRS Grade 4 Osteochondral Defect: A Case Report of Two Patients. (2026). https://doi.org/10.1155/cro/1667776 https://doi.org/10.1155/cro/1667776
2. [2] Editorial Commentary: Hip Chondral Defect Treatment Requires Cells, Signal, and Scaffold. (2022). https://doi.org/10.1016/j.arthro.2022.06.007 https://doi.org/10.1016/j.arthro.2022.06.007
3. [3] Assessment of the Correlation between Macroscopic ICRS Grading and Histopathological OARSI Scoring in Osteoarthritic Cartilage. (2026). https://doi.org/10.1177/19476035251393150 https://doi.org/10.1177/19476035251393150