Paediatric Ankle Fractures and Transitional Injuries

Paediatric ankle fractures account for about 5% of all paediatric fractures, and the distal tibial physis is one of the most important lower-limb growth plates injured in children. Management is high-stakes because the same injury can affect the joint surface, the physis or both.

Presentation. The typical patient is a child or adolescent with ankle pain, swelling and inability to weight bear after a twisting injury, a fall, a sports injury or higher-energy trauma.

Not an adult ankle. In children the ligament may remain intact while the physis or epiphysis fails. In adolescents, asymmetric closure of the distal tibial physis creates transitional injuries, the Tillaux and triplane fractures.

Work through the same questions in the same order for every injured paediatric ankle, safety first and follow-up last.

The distal tibial physis. It contributes meaningfully to tibial growth and closes asymmetrically: centrally first, then medially, laterally last. During this transition the partially closed physis cannot dissipate rotational force evenly.

Where the transitional fractures come from. The anterior inferior tibiofibular ligament (AITFL) attaches to the anterolateral distal tibial epiphysis. When the medial physis is closing and the lateral physis remains open, external rotation can avulse that anterolateral epiphyseal fragment, which is the Tillaux pattern. If the fracture propagates through the epiphysis, physis and metaphysis in different planes, the result is a triplane fracture.

The distal tibia and fibula. The distal tibia carries both a physis and a joint surface, so reduction must protect growth and articular congruity together. The distal fibula is often lower-risk, but do not miss a syndesmotic injury, physeal displacement or an associated distal tibial injury.

The medial malleolus. SH-III and SH-IV fractures here cross the epiphysis and physis and can damage the germinal layer. These medial injuries carry meaningful physeal-bar risk and need longer surveillance. Because the medial distal tibial physis can form a physeal bar, even small residual displacement may matter, and "small" here means smaller than the usual 2 mm rule. The numbers are set out under Investigations.

The injury pattern depends on the child's age, the mechanism and the stage of physeal closure.

Anchor the whole topic to a date. The distal tibial physis typically closes at about age 14 in girls and 16 in boys, and transitional fractures occur in the roughly 18-month window immediately before that closure completes. The window is therefore approximately 12.5 to 14 years in girls and 14.5 to 16 in boys.

Why the age matters. The same external-rotation force produces a physeal separation in a younger child, a Tillaux or triplane fracture in this narrow band, and an adult ankle fracture afterwards. That is why a "sprain" in a 13-year-old girl or a 15-year-old boy deserves more scepticism than the same story at 9 or at 19.

These ages are population averages rather than rules. Skeletal maturity varies by roughly two years either side of chronological age, so use the radiograph in front of you to judge how much physis is still open.

Salter-Harris. The classification relates the fracture line to the physis, metaphysis and epiphysis. In the distal tibia, types III and IV cross the articular surface, and type V, a compression injury, may only become evident when growth disturbance develops.

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Tillaux and triplane fractures are described by their fragments, and the Dias-Tachdjian system by the mechanism of injury.

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History. Establish the mechanism and energy, the ability to weight bear, the exact site of pain and the time since injury. Ask about any reduction attempt, an open wound, skin tenting, paraesthesia and a previous ankle injury. Sporting adolescents with external rotation mechanisms are the classic group for transitional fractures.

Examination. Look, feel and move, then check the neurovascular status and the compartments.

The differential. The trap in children is the radiographically subtle injury. A tender physis with a "normal" film is a fracture until proven otherwise, and a presumed sprain in a skeletally immature ankle should be treated with suspicion.

What to request. Start with AP, mortise and true lateral ankle radiographs, and add further studies when the findings call for them:

• Tibia/fibula views if proximal fibular pain, a high-energy mechanism, syndesmotic concern or a Maisonneuve-type pattern is possible
• Foot radiographs if there is midfoot, base of fifth metatarsal or talar tenderness
• CT for a suspected Tillaux, triplane or SH-III/IV fracture, intra-articular displacement, unclear fracture geometry or pre-operative planning

MRI is not routine for clear fractures, but may help when radiographs are negative and symptoms remain disproportionate, or when occult physeal injury is a concern.

The Tillaux on film and on CT. The plain-film clue is a subtle vertical lucency in the anterolateral epiphysis. CT is needed when the fracture line or displacement is uncertain; measure displacement in orthogonal planes and map the fragment before choosing casting or fixation.

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Assess the mortise, the physis, the articular surface and each named fragment in turn.

Periosteal interposition. Suspect it when a displaced SH-II fracture retains a physeal gap after a careful reduction attempt.

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Where the 2 mm figure comes from. The threshold is not arbitrary, but it is narrower than its everyday use suggests. It derives from Ertl 1988 (23 triplane fractures, Level IV), which found that residual displacement of 2 mm or more after reduction was associated with a less than optimum result, "unless the epiphyseal fracture was outside the primary weight-bearing area of the ankle".

The rule was always about where the step is as well as how big it is, so state the location with the measurement. A 3 mm step in the anterolateral corner outside the loaded zone is a different problem from a 2 mm step in the plafond.

Two caveats that pull in opposite directions. A later CT-based series (Choudhry, 78 transitional fractures) found no functional penalty up to 2.4 mm at a minimum of two years. Ertl's results, on the other hand, got worse with time: 20 of 23 patients were asymptomatic at 18-36 months, but only 8 of 15 remained asymptomatic when reviewed at 38 months to 13 years.

Short follow-up flatters these injuries, and a good two-year result is not proof of a good outcome at twenty. Treat 2 mm as a deliberately conservative working threshold in the weight-bearing plafond, and do not let a reassuring early review close the case.

The medial malleolus exception. Here the 2 mm test is the wrong instrument. In a series where every patient was reduced to within 2 mm, mean residual displacement was 1.2 mm in those who went on to form a bar and 0.8 mm in those who did not (P = 0.03). At this fracture the useful question is how close to zero the reduction is, so aim for anatomical rather than merely acceptable.

First steps. Control pain, elevate and splint, which reduces swelling and allows safe reassessment. Skin tenting or severe deformity needs urgent reduction and an open injury needs urgent theatre, to prevent skin compromise and contamination complications.

Around every reduction. Document pulses, capillary refill and sensation before and after reduction, which identifies injury-related or iatrogenic deterioration. Repeat AP, mortise and lateral films after any reduction to confirm alignment and residual displacement.

The decision turns on displacement and stability, pattern by pattern.

Implants. Implant choice does not replace the essential endpoints: restored alignment, stable fixation and a protected articular surface and physis. In SH-IV fractures the construct must follow the CT-defined fracture geometry while restoring the joint surface and limiting additional physeal injury.

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Principles. The operation should reduce the joint surface, respect the physis, avoid repeated traumatic manipulation and provide enough stability for safe healing. In Tillaux and triplane injuries CT determines the approach and the screw trajectory.

Positioning for arthroscopy-assisted reduction. The patient lies supine and fully draped, with the ankle accessible to imaging and instrumentation. The set-up must preserve fluoroscopic AP, mortise and lateral views and permit conversion to an open approach if the reduction remains unacceptable.

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Checking the reduction. Confirm the clamp path and the reduction in orthogonal views, then verify articular congruity before definitive fixation. Check wire trajectory, stability and proximity to the physis in both planes.

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What union cannot exclude. Early fracture union cannot exclude growth arrest: a partial physeal arrest may only show itself as asymmetric growth and progressive angular change.

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Detecting and Treating a Physeal Bar

Harris lines. Harris (Park) lines are transverse radiodense lines in the metaphysis that form when growth slows and then resumes, after injury, illness or chemotherapy. They are a useful early sign of how the physis is behaving.

A line parallel and symmetric to the physis indicates uniform resumed growth and is reassuring. A line that is asymmetric and converges towards, or is tethered to, the physis points to a focal area that has stopped growing, an early physeal bar. Looking at the orientation of the Harris line on surveillance films can flag a developing bar before frank deformity appears.

Beyond union. Children with intra-articular displacement, high-energy trauma, a medial malleolus injury or meaningful remaining growth should not disappear after fracture union. They need a surveillance plan until the risk of growth arrest is acceptably low.

Global epidemiology

Paediatric ankle fractures account for about 5% of all paediatric fractures, and distal tibial physeal injuries make up roughly 15-20% of all physeal injuries, making the distal tibia the most commonly injured lower-limb physis in children. Transitional fractures (Tillaux and triplane) cluster in the roughly 18-month window before physeal closure, which completes at about 14 years in girls and 16 years in boys. Boys are affected more often overall; girls sustain transitional fractures at a younger age than boys.

Side-by-side guidance

There is no single global ankle-specific paediatric guideline; practice is built from major-society principles plus the paediatric trauma literature. The points below describe how the relevant bodies frame the same problem.

Registries

Unlike arthroplasty, paediatric ankle fractures are not tracked by implant registries; the evidence base is observational cohorts and systematic reviews (for example the 2025 triplane review pooling 34 studies). National paediatric trauma networks and major-trauma audits, rather than implant registries, are the closest surveillance structures.

High-resource versus limited-resource practice

Examiners reward a candidate who can hold a clear default position while acknowledging genuine debate. The honest answer to most of these is anatomical reduction of the displaced joint, with the nuance below.