The ankle sprain that refuses to settle

An ankle sprain is one of the most common injuries there is — and one of the most commonly dismissed. The standard advice is rest, ice, compression, and elevation, and for most people that approach works well. Symptoms settle within six to twelve weeks, and life resumes. But for a meaningful number of patients, something else is happening beneath the surface, and no amount of physiotherapy or time seems to shift it.

The hallmarks are recognisable once you know what to look for: swelling that persists long after the bruising has gone, a deep aching inside the joint rather than soreness along the outer ankle, stiffness first thing in the morning or after sitting, and an occasional clicking or giving way that did not feature in the original injury. Patients often describe it as 'a sprain that never healed'. That description, heard frequently in specialist practice, is usually accurate — because in many cases the sprain was not the whole story.

An osteochondral lesion of the talus (OLT) involves damage to the cartilage surface on top of the ankle bone and to the layer of bone directly beneath it. Published data suggest these lesions occur in an estimated 50–70% of significant ankle sprains — not as an occasional complication, but as a frequent one. That figure is striking, yet most people who sustain a sprain are never assessed for one.

The gap between injury and diagnosis is often measured in months or years, not days. That delay is not inevitable; it is largely a consequence of routine imaging that is not sensitive enough to detect the lesion at the outset. Recognising the pattern of persistent, activity-related joint pain — distinct from simple ligament soreness — is the first step towards getting the right answer.

What actually gets damaged inside the ankle joint

The talus sits at the top of the ankle, cradled in a bony socket — the mortise — formed by the lower ends of the tibia and fibula. Its domed upper surface is covered by cartilage, which distributes load across the joint with every step. When an OLT forms, both that cartilage layer and the subchondral bone immediately beneath it are disrupted — a detail that distinguishes these injuries from a simple surface scratch and helps explain why they can be so slow to resolve.

Location matters considerably. Around 83% of talar osteochondral lesions arise on the medial (inner) side of the dome, with lateral lesions accounting for the remaining 17%. This is not random: varus lower-limb alignment — where the leg bows slightly inward — concentrates load on the medial talar surface and is independently associated with medial lesions. A history of recurrent lateral sprains, which allows chronic instability to develop, further raises the risk of medial lesion formation. Lateral lesions tend to follow a different biomechanical pattern and are more often linked to a single traumatic event.

Where exactly on the dome a lesion sits has consequences beyond size alone. Biomechanical modelling shows that lesions in the posteromedial and mid-posterior zones cause the greatest loss of joint stiffness — in some cases a more powerful determinant than lesion diameter — which is why location is weighed alongside measurements when treatment decisions are made.

Why standard X-rays miss the injury

The Ottawa Ankle Rules are a well-validated triage tool, and rightly so — they help clinicians decide quickly which patients need an X-ray to exclude a bony fracture. What they were never designed to do is detect damage to cartilage or the subchondral bone layer beneath it. That design limitation is at the heart of the diagnostic gap.

Plain radiographs cannot resolve cartilage — it is invisible to X-ray — and undisplaced osteochondral fractures often produce no obvious bony step that would flag on a standard film. Published estimates suggest up to 50% of OLTs are missed on initial X-ray for exactly this reason. The injury is there; the imaging simply cannot see it.

CT scanning offers better bony detail and has a role in pre-operative planning once a lesion is confirmed, but it shares the same fundamental limitation for initial diagnosis: cartilaginous lesions and non-displaced injuries remain invisible, and CT adds radiation exposure without resolving the core diagnostic question.

MRI is the investigation that closes the gap. It detects subchondral oedema, haemorrhage, and cartilage disruption that neither X-ray nor CT can visualise, and it does so in the acute phase — before a lesion has had the opportunity to enlarge or destabilise. A 2025 imaging review confirmed that early MRI also identifies co-existing soft-tissue injuries and bone contusions that directly shape treatment planning and rehabilitation goals. At MSK Doctors, AI-assisted MRI analysis through onMRI™ supports this interpretation, helping to characterise lesions with greater precision.

What happens when the diagnosis is delayed

Treating a persistent ankle injury as 'just a sprain' carries a cost that becomes apparent only later — and by then the clinical picture may have changed significantly.

For acute, non-displaced OLTs, conservative management — bracing, physiotherapy, protected weight-bearing, and anti-inflammatory measures — achieves a satisfactory outcome in roughly 50% of cases. That is a meaningful success rate, and it is the reason conservative care remains the appropriate first step. The difficulty is that, without imaging, there is no reliable way at the bedside to identify which patients fall into that 50% and which do not.

The lesions that do not resolve do not simply stay the same. Over months, an unrecognised injury can enlarge, develop subchondral cysts, or become mechanically unstable. The endpoint of that trajectory is tibiotalar — ankle — osteoarthritis, a condition that is predominantly post-traumatic in origin and that disproportionately affects younger, active adults. Unlike hip or knee OA, which tends to present in later decades, post-traumatic ankle OA is a leading source of chronic disability in people who are still decades from retirement.

Delay is not a neutral default. A lesion identified at six weeks — when it may still be small, stable, and amenable to the least invasive approaches — is a different clinical problem from the same lesion found eighteen months later, by which point the range of surgical options may have narrowed and outcomes become less predictable.

No randomised trial has directly compared early-imaging with delayed-imaging pathways on patient outcomes; that evidence gap is real. It is, however, a reason for specialist judgement rather than inaction. Early MRI serves as a decision-support tool: it identifies which lesions are unlikely to settle with conservative care before they enlarge, allowing a supervised watchful-waiting plan to be distinguished from a case that warrants prompt intervention.

What a proper ankle assessment involves

The first thing a specialist will want is the story: how the ankle twisted, whether there was immediate swelling or bruising deep in the joint, how symptoms have evolved since, and what treatments — if any — have already been tried. That narrative matters clinically because it shapes the probability of an underlying osteochondral lesion before a single image is obtained.

Examination follows. The consultant assesses ligament stability through stress tests, measures range of motion, palpates along the joint line for focal tenderness, and looks for signs of impingement — deep anterior pain at end-range dorsiflexion, for instance. These findings triage imaging urgency rather than confirm a diagnosis; physical examination alone cannot characterise cartilage or subchondral bone.

MRI is requested when symptoms persist beyond six to eight weeks without clear resolution, or earlier if the original injury was a high-grade sprain, if there is deep joint pain, or if haemarthrosis was evident acutely. That is the investigation that characterises lesion size, stability, and any co-existing soft-tissue or tendon damage — detail that guides the management plan from the outset.

Where lower-limb alignment or chronic instability forms part of the picture — as it frequently does in medial talar lesions — objective biomechanical assessment of load distribution and gait can add measurable data that static imaging does not capture, particularly when a return-to-sport decision is in question.

In younger and adolescent patients the threshold for MRI is lower still. Research has documented osteochondral avulsion of the distal fibula in 6–28% of children presenting with a suspected ankle sprain, making a high index of suspicion appropriate in this group even when initial X-rays appear normal.

Treatment options and realistic expectations

Smaller, stable, non-displaced OLTs detected at an early stage are generally offered a supervised course of conservative care first: a structured physiotherapy programme addressing strength and proprioception, load management, bracing during activity, and — where inflammation is a limiting factor — targeted injection support. That pathway is appropriate and often sufficient for lesions with favourable characteristics.

Where symptoms persist after three to six months of supervised conservative management, or where lesion size, cystic change, or displacement makes spontaneous healing unlikely, a surgical conversation becomes reasonable. The decision rests on the full clinical picture — lesion characteristics on MRI, the patient's activity goals, and biomechanical factors such as lower-limb alignment.

Arthroscopic bone marrow stimulation (microfracture) is the standard first-line surgical option for lesions under approximately 10 mm in diameter. Larger, cystic, or previously treated lesions typically require a cartilage restoration procedure — most commonly OATS (osteochondral autograft transfer), AMIC (autologous matrix-induced chondrogenesis), or osteochondral allograft. Each technique has a distinct indication and evidence base; the cartilage repair section of this site covers them in full.

Long-term outcome data from a series of 156 surgically treated patients report approximately 75% overall satisfaction, with OATS reaching 90% satisfaction and around 85% of patients returning to sport. Where chronic lateral ankle instability coexists, combined arthroscopic OLT treatment and ligament repair can achieve comparable functional recovery to sprain repair alone — but advanced-stage lesions carry a significantly higher risk of residual pain, a finding that forms an important part of any pre-operative discussion.

1. [1] Results of the AMIC® method in patients operated on for an osteochondral lesion of the talar dome at mean follow-up of 34 months. (2024). https://doi.org/10.1016/j.otsr.2024.104020 https://doi.org/10.1016/j.otsr.2024.104020
2. [2] Simultaneous Treatment of Osteochondral Lesion Does Not Affect Mid- to Long-Term Outcomes of Ligament Repair for Acute Ankle Sprain. (2022). https://doi.org/10.3389/fsurg.2022.816669 https://doi.org/10.3389/fsurg.2022.816669