Two overlapping problems, one injured ankle

An old ankle injury that still aches years later rarely has a simple explanation. The pain might stem from a small pocket of damaged cartilage and bone — a focal osteochondral defect on the surface of the talus — or from broader, diffuse joint-surface wear beginning to spread across the ankle. Often, it is both, arising from the same original trauma.

This distinction is not academic. A focal defect and early post-traumatic arthritis can feel almost identical to live with, and their appearances on imaging can overlap. But they follow different biological paths and, crucially, they respond to different treatments. Identifying which problem is present — and in what proportion — is what determines whether joint-preserving options are still available.

Unlike the knee, where osteoarthritis more commonly develops through age-related wear, ankle arthritis is predominantly caused by a previous injury: a fracture, a severe sprain, or ligamentous damage that disrupts the joint surface years before symptoms become disabling. That post-traumatic origin is also what creates the window for intervention — and the risk of missing it.

Why ankle arthritis is almost always post-traumatic

For most people who develop ankle arthritis, there is a definable moment of origin — a fracture on the ski slope, a ligament tear during sport, or a succession of ankle rolls that never quite settled afterwards. That is not coincidence. Post-traumatic disease accounts for the overwhelming majority of ankle osteoarthritis cases, a pattern quite unlike the knee, where most arthritis develops through age-related wear without a clear injury trigger.

Risk is not equal across injury types, and it accumulates in a dose-dependent way. Rotational ankle fractures and severe ligamentous sprains are the two most common precursors, but the specific fracture pattern carries weight. A Weber C fracture or a medial malleolus fracture confers substantially higher risk; individuals with three or more such risk factors go on to develop ankle PTOA in around 60–70% of cases. Intra-articular fractures are the most damaging because they break the articular surface and the underlying subchondral bone simultaneously — and then the surgery needed to stabilise them adds a second cellular insult, compounding the biological stress to the cartilage in the weeks that follow.

Repeated sprains without adequate rehabilitation follow a slower but equally real trajectory. Each inadequately healed episode leaves the joint marginally less stable, shifting load unevenly across the cartilage surface. Over years, that asymmetric loading produces the diffuse thinning and subchondral change that imaging typically reveals long before pain becomes disabling — making post-injury rehabilitation a matter of joint protection, not merely functional recovery.

Talar OCD: a focal defect within the bigger picture

Osteochondral lesions of the talus are far more common after ankle trauma than most patients realise — present in roughly 69% of ankle fractures and 70% of lateral ligament sprains. That striking prevalence means both pathologies discussed in this article frequently share the same traumatic origin, yet they diverge significantly in what happens next.

Unlike the diffuse surface thinning of post-traumatic arthritis, an OCD is primarily a focal disorder of the subchondral bone — the dense layer immediately beneath the cartilage. When that layer sustains a crack or area of poor blood supply, the cartilage above loses its structural foundation and breaks down in a contained, localised patch rather than spreading across the whole joint surface.

Location carries real diagnostic weight. On the inner (medial) side of the talar dome, defects tend to sit more posteriorly, run deeper into the bone, and often appear without any clear single-injury trigger — patients may report years of vague ankle ache rather than a recalled twist or fracture. Lateral defects behave differently: they are typically shallower, positioned more centrally or anteriorly, and almost always linked to a specific traumatic event. Lateral lesions are also less likely to resolve spontaneously.

Left untreated, OLT progresses to frank ankle arthritis in roughly one-third of patients — a risk that persists even following bone marrow stimulation. That figure reframes early diagnosis as genuine OA prevention, not merely lesion-specific management. Crucially, a patient may present with a focal defect alone, diffuse early wear alone, or both simultaneously — which is why accurate staging matters before any treatment decision is reached.

How the two conditions are told apart

Assessment begins before any scan is ordered. The conversation between patient and clinician — when the injury happened, whether the pain is sharp and localised or diffuse and aching, whether the ankle ever catches, locks, or gives way — already starts to separate the two pathologies. A clear traumatic antecedent, precise tenderness over the talar dome, and mechanical symptoms such as catching or locking point toward a focal defect. Diffuse morning stiffness, pain that follows activity globally rather than from a single spot, and tenderness spread across the joint line are more consistent with progressive cartilage wear.

Plain X-ray is the usual starting point: it identifies advanced lesions and overall joint space narrowing, but misses early-stage OCD where subchondral changes are often too subtle to register on film. The Berndt & Hardy classification — the standard radiographic framework for talar OCD — grades the degree of lesion displacement, so encountering it on a report indicates a structural description, not a treatment decision.

MRI is the primary tool for distinguishing the two conditions. Focal subchondral oedema, cystic change beneath the cartilage, and signs of fragment instability indicate OCD; diffuse joint space narrowing, global cartilage thinning, and widespread osteophytes indicate advancing PTOA. Importantly, both patterns can coexist in the same joint. Where MRI findings leave fragment size or bony stability in doubt, CT adds the precision needed — the Ferkel & Sgaglione system provides a structured staging framework across CT and MRI findings.

The broader principle matters more than any individual grading system: imaging describes anatomy, not a treatment mandate. An OCD sitting within an otherwise well-preserved joint represents a different clinical problem from an incidental defect found against a background of established arthritis. That distinction — reached through history, examination, and imaging read together — is what determines whether joint preservation remains a realistic option.

The preservation window: what treatment looks like while it is still open

The window stays open for as long as the joint surface retains enough integrity to be worth saving — a period that varies between patients but is defined practically by the absence of established bone-on-bone contact.

Conservative care first

The pathway begins before any intervention. Load management, targeted physiotherapy to rebuild peroneal and calf muscle control, orthotic support, and footwear modification can meaningfully reduce symptoms and slow progression in early-stage disease. For many patients, this is the mainstay of management for months, sometimes longer.

Biologic support at the conservative-to-intervention interface

PRP, hyaluronic acid, and adipose-derived cell therapies (mFat/BMAC) address the joint environment rather than the structural defect itself — reducing inflammation, improving lubrication, and providing a cellular substrate that may slow cartilage breakdown. They are applicable across both focal OCD and early diffuse PTOA, and often precede or accompany more targeted structural work.

Focal repair: defect size sets the approach

When an OCD lesion requires direct structural treatment, technique is guided principally by defect size. Smaller lesions under 10 mm are candidates for bone marrow stimulation (microfracture), which recruits progenitor cells from the underlying bone to lay down fibrocartilage repair tissue. Medium defects in the 10–20 mm range are better served by osteochondral autograft transfer (OATS), transplanting a plug of healthy bone and cartilage from a low-load donor site. Larger or structurally complex defects may require autologous chondrocyte implantation (ACI), a two-stage process using cultured cartilage cells. Injectable collagen scaffold options sit at the less invasive end of this spectrum, aiming to support matrix-induced chondrogenesis without theatre-based surgery — a meaningful distinction for patients who are not yet ready for operative intervention.

When alignment is the driver

If biomechanical malalignment or persistent ligamentous instability is accelerating cartilage wear, realignment osteotomy is considered alongside focal repair rather than instead of it — correcting the mechanical environment so that any repaired surface is not immediately overloaded.

What 'the window closing' means in practice

Once bone-on-bone contact extends across a significant portion of the joint surface, the clinical calculation shifts from preservation to replacement. No consensus threshold — no specific defect size or OA grade — marks that crossover precisely. What changes is the probability that any repair will hold under load; and that probability diminishes steadily as background diffuse arthritis advances alongside the focal lesion.

Getting the right assessment early

Three signals, in particular, warrant a specialist appointment rather than further waiting: ankle pain that persists beyond six to eight weeks after injury without clear improvement; mechanical symptoms — clicking, catching, a sense of the joint giving way; or a structured physiotherapy programme that has run its course without meaningful benefit.

A first consultation is straightforward. The clinician takes a detailed injury history, examines joint range and stability, and reviews any imaging already to hand — or arranges it if none exists. That assessment builds a picture of both the focal and the diffuse components: whether there is an osteochondral lesion, how much background wear is present, and where the joint sits relative to the preservation window.

Timing matters more here than in most joint conditions. The same ankle injury assessed promptly may still offer scope for joint-preserving treatment; the same ankle left unreviewed for several years may have moved past that point. Earlier assessment does not guarantee a simpler solution, but it keeps more options in play.

Liquid Cartilage™ — the ChondroFiller injectable collagen scaffold — is available at the London Cartilage Clinic on Harley Street, where a consultant can determine whether the defect size, lesion stage, and degree of background wear make an image-guided outpatient approach appropriate. The preservation window, in other words, has to be identified before it can be used.

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