Lateral Ankle Sprain (ATFL/CFL)

Who: Anyone, any sport, any uneven footpath. Highest rates in indoor and court sports, and — a detail worth knowing — higher in females and in children than adults.
What: Sudden inversion, lateral ankle pain, swelling and bruising. Difficulty weight-bearing.
How it behaves: Acutely traumatic, then mechanical. Settles fast in the first fortnight, then plateaus.

The illness script in one line: a sudden inversion injury with lateral swelling and tenderness, where your first job is to rule out fracture, your second is to check it isn't a high ankle sprain, and your third is to stop treating it as trivial.

The numbers that matter:

([1], 181 prospective studies. No confidence intervals reported. Lateral ankle sprain was the most common type.)

Ankle sprain is roughly 14% of all sport-related injury, and about 80% of those are ligamentous inversion sprains ([2], narrative review — treat that figure as reported, not pooled).

⚠️ No Australian management guideline exists for this presentation; for the X-ray decision, NSW's emergency care protocol uses the Ottawa Ankle Rules. Anchored to the JOSPT Ankle Stability and Movement Coordination Impairments CPG [3], with the Dutch multidisciplinary guideline (Vuurberg 2018) and the ROAST assessment consensus (Delahunt 2018) alongside. The closest Australian material is primary research, not guidance.

Pattern > Label. ATFL versus CFL is not the decision. The decisions are: fracture or not, syndesmosis or not, and how hard are you going to load this.

Traumatic onset, so run the UniSA order for trauma: MAIN PROBLEM → BODY CHART → HISTORY → BEHAVIOUR. The mechanism is the story here, so get it before anything else.

MAIN PROBLEM

"What's the main problem today?" — then the two that follow it everywhere in this pattern: can you walk on it, and what do you need to get back to.

BODY CHART

• Lateral ankle, over and anterior to the lateral malleolus — the ATFL. Pain over the CFL sits lower and slightly posterior.
• Map it above the joint line too. Pain proximal to the ankle joint, up the shin, is the syndesmosis question (§3).
• Clear the base of the fifth metatarsal, the navicular, the whole fibula to the head, and the medial malleolus. The proximal fibula is a separate associated-injury assessment, outside the Ottawa ankle/foot rule sites. The chart is a symptom map, not a fracture-screening diagram.

HISTORY — the mechanism does most of the work

• Inversion and plantarflexion → lateral ligaments. This is the common one.
• Dorsiflexion plus external rotation → syndesmosis. Different injury, different timeline, different conversation.
• Ask about the noise, the swelling speed, and whether they kept playing. Immediate marked swelling and an inability to continue is a more severe injury until proven otherwise.
• Previous sprains — this is the single strongest risk factor and the whole reason you're going to bother with rehab [4].
• What footwear, what surface, and had they done anything different that week.

The mechanism worth understanding, because it changes what you tell them — and it is worth saying out loud to the patient, because it reframes blame and builds trust: the injuring motion happens in roughly 50 ms. Peroneal reaction time is 60–90 ms (Fong 2009). The muscle cannot get there in time. So "you should have caught it" and "your ankle is weak" are both wrong — what training changes is what happens before the foot lands, and what happens on the next thousand landings.

BEHAVIOUR

• Aggs: weight-bearing, push-off, uneven ground, inversion, end-range plantarflexion, stairs.
• Eases: rest, elevation, compression, non-weight-bearing.
• Severity and irritability: vigour, severity, time to settle. It sets how much you do today.

SPECIAL / SCREENING QUESTIONS

General health, diabetes, previous ankle surgery, medications, and any neurological symptoms in the foot.

Top competing patterns, one discriminating feature each. Rule out the dangerous one first.

The base rates that should change your index of suspicion

It's tempting to treat syndesmosis and osteochondral lesions as edge cases. On 3-T MRI within 10 days of an acute ligamentous ankle injury in 171 injuries [5]:

• Anterior syndesmosis injury in 38%
• Cartilage or osteochondral lesion in 14% (85% of them cartilage rather than osteochondral)
• Lateral ligament injury in 73%

Those are much higher numbers than students expect. A "simple sprain" frequently has something else in it. That doesn't mean scanning everyone — it means the ankle that isn't following the expected recovery curve deserves a second look rather than a longer stretch.

Jones' hypothesis categories that change your plan here: precautions (fracture first, always), sources of symptoms (which structure, and is there more than one), and prognosis (recurrence risk drives your whole plan).

Swelling out of proportion to pain is a lateral sprain. Pain out of proportion to swelling is a syndesmosis until you've checked.