What an OLT actually is

A scan report showing a 'talar osteochondral defect' — also labelled 'osteochondral lesion of the talus' or 'OCD of the talus' in some letters and journal articles — describes the same thing: damage to both the smooth cartilage surface of the talus and the layer of bone directly beneath it. The talus is the bone that sits at the very base of your ankle, forming the joint between the lower leg and the foot.

Three overlapping mechanisms produce this injury: a single significant trauma such as an ankle fracture or severe sprain; repeated smaller stresses that accumulate over time (common in impact sports); and impaired blood supply to the bone itself, sometimes called ischaemia. In practice, more than one factor is usually at work.

The talus is structurally vulnerable in a specific way. Unlike most other bones, it has no muscle attachments and no blood vessels entering the bone directly — it relies entirely on vessels arriving from surrounding soft tissue. Certain zones of the dome receive a comparatively poor supply, and after injury these watershed areas can develop bone cell death (osteonecrosis) rather than healing normally.

Covering roughly 70% of the talar surface, articular cartilage also has limited capacity for self-repair, so when both the cartilage and the underlying bone are affected, the consequences for ankle mechanics can be significant.

OLTs are not rare findings: they are identified alongside approximately 69% of ankle fractures and 70% of ankle sprains, and around one in ten cases affects both ankles.

Symptoms and what they feel like day to day

For many people, the first sign is a deep, aching pain inside the ankle joint — not on the outer surface, but felt through the joint itself, particularly when standing, walking, or pushing off during sport. Swelling that appears after activity and settles with rest is common, as is a sense of stiffness that is worst after periods of inactivity.

Mechanical symptoms — a click, catch, or a brief locking sensation mid-movement — are a more specific warning sign. They suggest a fragment of bone or cartilage has become partially or fully detached and is intermittently catching within the joint. When this happens, the ankle may briefly feel as though it is jamming or giving way, which patients sometimes confuse with ligament instability.

One pattern that often surprises people is that lateral (outer dome) lesions frequently cause more pain than medial ones, even though they tend to be smaller and shallower. The reasons are not fully understood, but the consistent clinical observation is that lesion size on imaging does not reliably predict symptom severity.

That disconnect runs in the other direction too. Some OLTs are found purely by chance — on a scan ordered after an unrelated ankle injury — and cause no symptoms whatsoever. A structural finding on imaging is one piece of clinical information, not an automatic verdict that treatment is required. What prompts specialist assessment is the combination of persistent pain, typically lasting more than three months despite rest and conservative measures, alongside a scan finding that fits the clinical picture.

The Berndt and Harty grading system

Clinical letters and radiology reports routinely quote a stage number from the Berndt and Harty classification, a system first published in 1959 that remains the reference framework for grading OLTs on plain X-rays. Understanding the four stages — and a fifth added later — makes that shorthand meaningful.

Stage I is a subchondral impaction fracture: the bone beneath the cartilage has been compressed, but the surface is intact and no fragment is visible. On a standard X-ray, Stage I lesions are almost always invisible.

Stage II describes a partially detached osteochondral fragment — bone and cartilage have begun to separate, but the fragment still has some attachment. Again, this is frequently missed on plain radiographs.

Stage III means the fragment is completely detached but has not moved from its crater. It sits undisplaced within the defect, which is why it can still be easy to overlook without cross-sectional imaging.

Stage IV is the stage most readily visible on X-ray: the fragment has displaced and is moving freely inside the joint as a loose body.

Stage V — added in a later modification — refers to subchondral cyst formation beneath the lesion, a finding that requires CT or MRI to detect.

Because Stages I–III are commonly invisible on plain film, a normal-looking X-ray does not exclude significant damage, which is why MRI or CT is almost always requested next. Berndt and Harty staging provides the starting framework for a clinical conversation, but the grade alone does not determine treatment — symptom severity, lesion size, and bone involvement all feed into that decision.

What MRI adds: the Hepple staging system

Plain X-rays establish the starting framework, but most of what matters clinically about an OLT lies beneath the cartilage surface — territory that only cross-sectional imaging can map.

MRI at 1.5 Tesla is the current gold standard for staging. A single scan can show cartilage signal change, bone marrow oedema, haemorrhage, and fragment stability simultaneously, picking up lesions that are entirely invisible on plain film. The Hepple MRI staging system — five stages, developed specifically for this modality — gives clinicians a language for what the scan shows:

• Stage 1 Cartilage signal change only; the underlying bone is normal.
• Stage 2a Cartilage damage with a subchondral fracture line and surrounding bone marrow oedema, indicating active bone injury.
• Stage 2b The same cartilage and fracture findings, but without bone marrow oedema — suggesting a more chronic or quiescent process.
• Stage 3 The fragment is completely detached but still sitting in its crater, undisplaced.
• Stage 4 The fragment has moved and is loose within the joint.
• Stage 5 Subchondral cyst formation beneath the defect.

In practice, Hepple and Berndt and Harty are used together rather than as alternatives. Berndt and Harty provides the surgical decision threshold; the Hepple system adds detail about bone marrow involvement and cartilage status that the X-ray system simply cannot capture. Patients who receive a report referencing both sets of stages can therefore expect to see two stage numbers — they describe the same lesion, read through different lenses.

CT contributes at the preoperative planning stage: it defines bony defect dimensions, lesion depth, and articular morphology in multiple planes, and scanning with the ankle in maximum plantarflexion can help assess arthroscopic accessibility. However, CT cannot visualise cartilaginous or non-displaced lesions and adds little to early diagnostic staging.

For cases where precise cartilage grading is needed, cone-beam CT arthrography (CBCT-A) is an emerging specialist option. Its superior spatial resolution outperforms standard 1.5T MRI for assessing thin articular cartilage, though it remains a specialist-level rather than routine investigation.

How your grade shapes treatment

Grading is not an academic exercise — it directly determines what happens next in the clinic.

For Stages I and II, the default starting point is conservative management: a period of relative rest, targeted physiotherapy to offload the ankle, and activity modification. Joint-support injections are sometimes used alongside rehabilitation to reduce inflammation and support the joint environment while the lesion is given time to settle. Many lower-grade lesions do not progress, and some improve without any further intervention.

Lesion size and depth sit alongside stage as treatment determinants. A stable Stage II lesion under 15 mm across and less than 7 mm deep tends to behave differently from one that is larger or involves a cystic component beneath it — even if both carry the same stage number. These dimensions, read from the MRI or CT report, feed directly into the escalation decision.

When Stage III or IV lesions remain symptomatic — or when a lower-grade lesion fails to improve with conservative care — surgical intervention becomes a realistic next step. For smaller, contained defects, bone marrow stimulation (microfracture or drilling) is the standard first-line surgical approach, disrupting the subchondral plate to recruit repair cells into the defect. Larger lesions, deeper cysts, or cases where stimulation has not achieved adequate repair typically require reconstruction: osteochondral autograft transfer, mosaicplasty, or allograft transplantation, with the choice depending on defect dimensions and donor-tissue availability.

Between conservative management and formal surgical reconstruction, injectable collagen scaffolds delivered as an ultrasound-guided outpatient procedure represent a newer minimally invasive option for selected focal defects. These work by providing a structural matrix that supports the body's own progenitor cells in forming replacement cartilage — sitting on the treatment ladder between rehabilitation-led care and theatre-based surgery.

Getting an assessment in London

Ankle pain that persists for more than six to eight weeks after a sprain or fracture — or symptoms such as locking, catching, or giving way — warrants a specialist opinion rather than continued observation. These features suggest the joint is not simply healing on its own timescale, and earlier assessment allows staging to happen while treatment options remain at their broadest.

A specialist consultation typically covers clinical history, physical examination of the ankle, and review of any imaging already obtained. Where imaging has not yet been done, MRI is usually the first investigation requested. CT or cone-beam CT arthrography may follow later if the clinical picture points towards surgical planning — not as a routine first step, but to resolve specific questions about defect geometry or arthroscopic access.

The assessment outcome determines whether conservative physiotherapy-led care, an injection-based approach, or surgical referral best fits the lesion's grade and the patient's circumstances. That answer depends on the full clinical and imaging picture — not on a stage number alone.

Specialist ankle cartilage assessment, including evaluation for the ChondroFiller injection as an outpatient option for eligible focal defects, is available in London at the London Cartilage Clinic on Harley Street. Liquid Cartilage™ is delivered in the UK at the London Cartilage Clinic; assessments can be booked via londoncartilage.com.

1. [1] Fresh osteochondral allograft transplantation (FOCAT) for definitive management of a large OLT: A case report. (2019). https://doi.org/10.1016/j.foot.2019.09.001 https://doi.org/10.1016/j.foot.2019.09.001
2. [2] Treatment of Osteochondral Lesions of the Talus in Athletes. (2017). https://doi.org/10.5763/KJSM.2017.35.2.77 https://doi.org/10.5763/KJSM.2017.35.2.77
3. [3] Treatment of talar osteochondral defect with peroneus longus tendon autograft. (2022). https://doi.org/10.47482/acmr.1095702 https://doi.org/10.47482/acmr.1095702
4. [4] Staging of Osteochondral Lesions of the Talus: MRI and Cone Beam CT. (2017). https://doi.org/10.5334/jbr-btr.1377 https://doi.org/10.5334/jbr-btr.1377