High Ankle Sprain (Syndesmosis Injury)

Patients describe an external rotation or hyperdorsiflexion mechanism (pivot, tackle, ski fall) with anterolateral ankle pain often felt higher than a classic lateral sprain. Weight-bearing and push-off are painful, often disproportionate to the visible swelling. Patients frequently underestimate the injury and present with a slow-to-settle ankle sprain.

Examination:

• •Tenderness over the AITFL (anterolateral, just above the ankle line)
• •Swelling often modest compared with lateral sprains
• •Provocation tests (most useful in combination; no single test is definitive):

- Squeeze test (Hopkinson): proximal calf compression reproduces distal syndesmotic pain (high specificity) - External rotation stress test (Kleiger): pain on foot external rotation, in neutral (stresses the deltoid) and in dorsiflexion (stresses the syndesmosis) - Fibular translation test: anterior or posterior drawer of the fibula assesses mechanical syndesmotic instability - Cotton test: coronal mortise instability

• •Syndesmosis tenderness length (tenderness extending proximally) correlates with injury severity and recovery time
• •Always palpate the proximal fibula, assess the deltoid, and screen the peroneals

Red flags: proximal fibular tenderness (Maisonneuve) or medial tenderness with lateral injury; tense swelling, pallor, or neurovascular deficit (compartment syndrome or vascular compromise); open wound, gross deformity, or dislocation; progressive pain or instability after initial management (suspect missed injury).

Clinical assessment is the starting point. The Ottawa Ankle Rules (NICE CKS Sprains and Strains) are the standard decision tool for whether an ankle X-ray is needed in acute injury - inability to weight-bear 4 steps is one trigger, not a stand-alone red flag.

Plain radiographs (weight-bearing AP, mortise at 15 to 20 degrees internal rotation, and lateral) are first-line. Classic teaching thresholds for diastasis are tibiofibular clear space (TFCS) greater than 6 mm; tibiofibular overlap under 6 mm on AP or under 1 mm on mortise; and medial clear space greater than 4 mm or asymmetry versus the uninjured side (suggesting deep deltoid rupture and mortise instability). Plain-film measurements have anatomical and inter-observer variability, and normal static values do not exclude subtle or dynamic instability.

Weight-bearing or stress views unmask subtle (Grade II) injuries missed on non-weight-bearing films. Bilateral weight-bearing CT is increasingly useful for subtle or occult instability when plain radiographs are inconclusive; access and protocols vary by UK centre. Point-of-care ultrasound allows dynamic AITFL assessment and detection of dynamic diastasis under stress and is a core SEM and MSK competency. MRI is sensitive for AITFL/PITFL/interosseous injury, osteochondral lesions, and bone oedema; it is most useful when surgical decision-making is uncertain or associated soft-tissue or osteochondral injury is suspected.

If proximal fibular tenderness is present, obtain whole-leg radiographs (not ankle films alone) to exclude Maisonneuve. If initial imaging is normal but stability remains uncertain, early specialist follow-up with repeat radiographs (ideally weight-bearing if tolerated) within 2 weeks is appropriate per BOAST 12.

UK practice draws on BOA/BOFAS consensus and BOAST 12. A missed or undertreated syndesmotic injury is a leading cause of persistent pain and chronic syndesmotic instability.

Acute phase (0 to 48 hours) follows the PEACE & LOVE framework (preferred over POLICE in UK practice). PEACE: Protection, Elevation, Avoid anti-inflammatories, Compression, Education. LOVE (after 48 to 72 hours): Load, Optimism, Vascularisation, Exercise. Analgesia: paracetamol; topical NSAID is reasonable per NICE CKS. Avoid oral NSAIDs in the first 48 to 72 hours (may impair the inflammatory phase of ligament healing); consider short courses thereafter. A CAM boot is commonly used where pain, instability concern, or difficulty weight-bearing makes it helpful.

Grade I (stable): non-operative CAM boot with progressive weight-bearing per symptoms (typically 2 to 6 weeks); early structured physiotherapy. Return to sport broadly 6 to 8 weeks (often longer than comparable lateral sprain), criteria-based.

Grade II (intermediate): non-operative trial appropriate in many cases with a CAM boot, structured rehabilitation, and careful review. Threshold for specialist orthopaedic or foot and ankle referral is low for dynamic imaging (weight-bearing CT or stress views) - if dynamic instability is demonstrated, surgical stabilisation is typical. Return to sport broadly 3 to 4 months, highly variable.

Grade III (unstable): orthopaedic referral and surgical stabilisation with syndesmotic screws or dynamic fixation (e.g. suture-button). Suture-button fixation is an accepted option per NICE HTG374 and may reduce reoperation and hardware-related problems compared with screws; evidence for clearly faster recovery or superior return to sport remains less definitive. Return to sport broadly 4 to 6 months, highly variable.

Referral: FCP or advanced practitioner physiotherapist or GP for initial triage; urgent orthopaedic referral for any suspicion of unstable injury, Maisonneuve, mortise widening, neurovascular compromise, or open injury; SEM or foot and ankle clinic for persistent pain or instability beyond 6 to 8 weeks of appropriate non-operative care.

• •Phase 1 (0 to 2 weeks): protection in CAM boot if indicated, pain and swelling control, gentle pain-free ankle ROM
• •Phase 2 (2 to 6 weeks): progressive weight-bearing as tolerated, graded calf and intrinsic foot strengthening, proprioception, neuromuscular control
• •Phase 3 (6 to 12 weeks): sport-specific strengthening, plyometrics, agility, cutting drills
• •Phase 4 (return to sport): criteria-based with pain-free weight-bearing, normal single-leg hop symmetry, sport-specific drill completion, and psychological readiness

Many athletes return to sport with a lace-up brace or ankle tape initially. Re-injury prevention requires progressive neuromuscular training, proprioception, and attention to cutting and landing technique. Incomplete rehabilitation is a strong modifiable driver of persistent pain and chronic instability.

• •BOAST 12 (BOA Standards for Ankle Fracture Management) - syndesmotic principles for mortise stability, dynamic assessment, and surgical timing.
• •NICE HTG374 - dynamic suture-button fixation is an accepted alternative to screw fixation for acute disruption of the distal tibiofibular syndesmosis.
• •PEACE & LOVE consensus (Dubois & Esculier, BJSM 2019) - modern UK acute soft-tissue injury framework; avoid NSAIDs in the first 48 to 72 hours.
• •BJSM consensus on chronic ankle instability - inadequate rehabilitation is a strong modifiable predictor of persistent pain and chronic syndesmotic instability.
• •NICE CKS: Sprains and Strains / Ottawa Ankle Rules - decision tool for whether ankle X-ray is needed in acute injury; inability to weight-bear 4 steps is one trigger, not a sole red flag.

• •Consider high ankle sprain in any bad ankle sprain that is slow to recover or has disproportionate pain on weight-bearing. AITFL is the most commonly injured syndesmotic ligament.
• •Mechanism is external rotation or hyperdorsiflexion with the wider anterior talar dome acting as a wedge to force the tibia and fibula apart.
• •Always palpate the fibula to its head to exclude Maisonneuve; if suspected, obtain whole-leg radiographs, not ankle films alone.
• •Squeeze and external rotation stress tests are most useful in combination; no single bedside test is definitive. The fibular translation test adds mechanical assessment.
• •X-ray thresholds: TFCS over 6 mm; overlap under 6 mm (AP) or under 1 mm (mortise); medial clear space over 4 mm. Normal static films do not exclude dynamic instability - weight-bearing or stress views detect subtle Grade II injuries.
• •Grade I non-operative; Grade III almost always surgical stabilisation; Grade II is the key decision point. PEACE & LOVE is the current UK framework; missed or undertreated syndesmotic injury is a leading cause of persistent pain.