What the MRI grade is actually telling your surgeon

Patients leaving an MRI appointment often come away with a phrase like 'Grade II OCD' written in their report — a number that can feel both specific and oddly uninformative at the same time. What the grade is actually communicating is a shorthand for lesion stability, and it is stability — not the grade number itself — that sits at the fork in the treatment road.

The most widely used framework is the ICRS (International Cartilage Repair Society) scale, which runs from Grade I (cartilage surface intact, underlying bone affected but stable) through to Grade IV (the fragment has broken entirely free and floats loose inside the joint). Grades I and II are classed as stable; Grades III and IV as unstable. It is worth knowing, though, that a 2022 systematic review counted 33 competing OCD classification systems across radiology, MRI, and arthroscopic practice — so the grade number on a report may come from a slightly different framework depending on where the scan was read.

The real clinical work happens on T2-weighted sequences, where radiologists look for four specific signs that indicate a fragment is becoming unstable: a bright-signal rim running along the boundary between the fragment and the surrounding bone; a fluid-filled cyst sitting behind the lesion; disruption signal cutting through the overlying articular cartilage; and any displacement or free movement of the fragment itself. Together, these signs produce the binary verdict — stable or unstable — that the surgeon needs before choosing a pathway.

Here lies a practical gap worth knowing about. A 2016 study published in Academic Radiology found that only 56% of real-world MRI reports explicitly labelled a lesion as stable or unstable. That means a significant proportion of patients receive a grade number without the stability conclusion that gives the number its clinical meaning. If a report lists a grade but does not state whether the lesion is stable or unstable, that is a specific question worth raising with the specialist before any treatment discussion begins.

Why skeletal maturity changes the meaning of the same grade

Grade alone, then, does not complete the clinical picture. A second factor — skeletal maturity — determines what that grade is actually worth, and it can point two patients with identical MRI findings in entirely opposite directions.

The dividing line is whether the growth plates (physes) are still open. In younger patients whose physes remain open, juvenile OCD carries a genuine capacity for spontaneous healing; with activity restriction and careful monitoring, over half of Grade I–II cases in this group resolve fully within 6 to 18 months. In a skeletally mature adult whose physes have closed, the same Grade II lesion is unlikely to heal without intervention regardless of how long conservative measures are pursued.

This creates a clear decision point at Grade II specifically. A 14-year-old with open physes and a stable Grade II lesion may be a reasonable candidate for a structured period of conservative management and serial MRI review. A 28-year-old with closed physes and the same grade would typically be considered for surgery from the outset, because the biological conditions for spontaneous repair are no longer present.

Physeal status can be confirmed on MRI or a plain radiograph, and patients are entitled to ask their specialist which category applies to them. It is one of several variables — alongside grade, lesion size, and symptoms — that the specialist must integrate before any treatment decision is made.

Conservative management: who it works for and what it involves

For those who meet the criteria — Grade I or II, skeletally immature, with open physes — conservative management is a structured clinical commitment rather than passive waiting. It typically involves genuine activity restriction, bracing or casting, and a period of non-weight-bearing that runs to three to six months, all tracked by serial MRI at agreed intervals. The imaging follow-up is not incidental: it is the mechanism by which the clinician confirms that subchondral bone is remodelling in the right direction before any decision is made to progress.

The evidence supports this pathway with reasonable confidence at the stable end of the scale. Published data suggest conservative treatment succeeds in approximately 78% of Grade I–II lesions — a meaningful figure, though one that depends on patients maintaining the required level of unloading throughout. This is not a protocol that tolerates early return to running or impact sport; partial adherence tends to compromise the result.

The Grade III–IV picture is materially different. Studies indicate a fivefold increase in conservative failure risk once a lesion crosses into unstable territory, which is the evidence-based reason the stable/unstable threshold carries so much weight in the treatment algorithm. For unstable lesions, extended conservative management typically delays rather than avoids surgery, and the specialist will usually say so clearly.

When conservative care is appropriate, the accepted signal to escalate is the absence of measurable MRI improvement after four to six months. Continued pain alongside static or worsening imaging at that point is grounds for a surgical discussion — not because conservative management has failed the patient, but because the biological window has been given a fair trial and the lesion has not responded.

The surgical threshold and what tips the decision

Surgery is not triggered by grade alone. The specialist integrates four distinct criteria, and any one of them — not necessarily a combination — may be sufficient to cross the threshold.

• Grade III or IV on MRI — a partially or fully detached fragment is unlikely to stabilise without surgical intervention; the mechanical environment of a loose or displaced fragment prevents the biological repair process from taking hold
• Skeletal maturity — closed physes change the calculus entirely; adult OCD is almost always managed surgically regardless of grade, a point the preceding section covers in detail
• Lesion area exceeding 2 cm² — a practical size threshold beyond which the fragment's mechanical load on the joint surface increases substantially; this is a clinical guide, not an absolute rule, and must be weighed alongside fragment location, viability, and patient age
• Failure of structured conservative management — where serial imaging has shown no measurable improvement, as outlined above

The size threshold is worth emphasising because it is sometimes overlooked in the conversation about grades. A larger Grade II lesion in a skeletally mature adult may cross the surgical line on size alone, even if the cartilage surface appears nominally intact on T2 sequences.

At a specialist appointment, the most useful question is not simply 'what grade am I?' but which of these four criteria applies — and whether more than one is in play. That combination determines not only whether surgery is indicated, but what form it should take.

Surgical technique depends on what is left of the fragment

Once the decision to operate is made, the surgeon's next question is simpler but no less consequential: is there still something worth saving?

Fragment viability — assessed during the procedure itself — is the first fork in the surgical decision tree. Where the detached or partially separated fragment remains viable, the preferred approach is refixation: the fragment is held in place with internal fixation and allowed to heal back to the parent bone. This is not simply a matter of clinical preference. A 14-year follow-up study by Bangert (2023), covering 37 surgically treated patients, recorded mean IKDC and Lysholm scores of 91.3 and 91.7 respectively; the best outcomes in the series were consistently associated with refixation.

For Grade II lesions where the cartilage surface is still intact, a less invasive option exists: retrograde drilling, which creates vascular channels through the underlying bone to stimulate healing without disturbing the articular surface itself.

Where the fragment is non-viable or has already been removed, the surgeon is left with an open defect. Three broad repair strategies then apply, chosen primarily by defect size — and naming them up front makes the terminology easier to follow. Smaller defects (under roughly 2–4 cm²) are typically addressed with microfracture (marrow stimulation) or mosaicplasty (transfer of healthy osteochondral plugs); long-term data favour mosaicplasty at this size range. For larger defects of 3 cm² or more, MACI — matrix-induced autologous chondrocyte implantation — has demonstrated superior KOOS pain and function scores compared with microfracture in the SUMMIT trial.

The Bangert dataset, widely cited as the most robust long-term evidence available, followed 37 patients. The outcomes are genuinely encouraging, but the evidence base remains limited in scale and patients should weigh the numbers with that in mind. This is one more reason why the initial MRI reading matters: the stability grade it assigns shapes which of these surgical paths remains open.

Practical questions to raise at your specialist appointment

Three questions are worth writing down before your specialist appointment.

The first: 'Does my MRI report explicitly say stable or unstable?' A 2016 study found that only 56% of clinical MRI reports included this label — meaning a grade number, without the accompanying stability interpretation, leaves the treatment decision without its entry point. If your report does not state it, ask.

The second: 'How does my skeletal maturity change what this grade means?' As the earlier sections set out, the same Grade II finding carries different implications depending on whether physes are open or closed — and a specialist can confirm which category applies.

The third: 'How large is the lesion, and does that affect the options if conservative management fails?' Size influences both the surgical threshold and the techniques that remain available, so knowing the defect area is useful early, not only if escalation becomes necessary.

For stable or early Grade II lesions where observation is continuing but surgical refixation is not yet indicated, it is also worth asking whether an injectable collagen scaffold — ChondroFiller injection — belongs in the biological support pathway for your lesion profile. A specialist assessment is needed to determine whether the size, stability, and location make it relevant to your case.

Patients in London can book an assessment at the London Cartilage Clinic on Harley Street (londoncartilage.com).

The reason all of these questions carry weight is the same: untreated or inadequately managed OCD at Grade III–IV carries a recognised risk of premature osteoarthritis. The grade on an MRI report is not just a descriptor — it is the point at which timing, maturity, and lesion biology converge into a decision that has long-term consequences for the joint.

1. [1] Osteochondritis dissecans — Wikipedia. https://en.wikipedia.org/?curid=3762029 https://en.wikipedia.org/?curid=3762029