Transitional Fractures: Tillaux and Triplane

Transitional fractures are unique pediatric ankle injuries occurring during the 18-month period of asymmetric distal tibial physeal closure.

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Physeal Closure Pattern (CML):

• The distal tibial physis closes asymmetrically over approximately 18 months.
• Central portion closes first (age 12-13).
• Medial portion closes next (age 14-15).
• Lateral (anterolateral) portion closes last (age 15-16).

Hence the name "triplane" - three planes of fracture.

Most triplane fractures are lateral - the epiphyseal fragment is anterolateral, as described above - but two less common variants are examinable because they behave differently and are easy to miss if you assume every triplane exits laterally.

The unifying principle is unchanged: define the fragments and the articular exit on CT, and reduce any step within the weight-bearing plafond to under 2 mm. The reason to recognise the medial variant specifically is that it appears in a slightly younger patient with more growth remaining, so the standard reassurance about growth arrest is less absolute than for the classic late-adolescent lateral Tillaux/triplane.

Differentiation from Adult Ankle Fractures:

• Age is the key factor.
• In adolescents, the physis is weaker than the ligaments.
• Similar mechanisms cause physeal fractures, not ligament sprains.

The anterolateral painful adolescent ankle after a twisting injury has a tight differential. The pivotal discriminator is patient age and physeal status - the same external-rotation force produces a ligament sprain in an adult but a physeal fracture in an adolescent because the open physis is weaker than the AITFL.

Intraoperative Tips:

• Use fluoroscopy liberally to confirm reduction.
• The articular surface should be anatomic (less than 1-2mm step).
• Avoid screw penetration into the joint.

Although growth arrest is usually inconsequential in the late-adolescent Tillaux or lateral triplane, the risk is not zero - and in younger patients (and the medial variants above) a partial physeal bar can produce angular deformity or leg-length discrepancy. Examiners expect you to know how you would detect and manage it, not simply assert that it "rarely matters."

Detection

• Surveillance to skeletal maturity in the younger or higher-risk patient, with comparison radiographs of the contralateral limb.
• Harris (growth-arrest) lines: a transverse sclerotic line laid down after the injury. A line that stays parallel to the physis indicates symmetric resumed growth; a line that is asymmetric or converges toward the physis points to a tethering bar at the point of convergence.
• Cross-sectional bar mapping: CT or MRI to locate and size a suspected physeal bar, expressed as a percentage of the physeal area, which guides treatment.

Management

The practical rule: the closer to skeletal maturity, the less you need to do - the classic late-adolescent Tillaux essentially needs nothing - but a younger patient deserves follow-up because a partial bar is treatable if it is caught early.

Hardware:

• Screws are usually left in situ unless symptomatic.
• No routine removal needed.

Global epidemiology:

• Triplane fractures account for approximately 5-10% of paediatric intra-articular ankle injuries (Schnetzler & Hoernschemeyer 2007); juvenile Tillaux is rarer.
• Peak age 12-15 years, with triplane tending to occur slightly younger than Tillaux because more of the physis remains open.
• Slight male predominance; mechanism is external rotation across a narrow window of asymmetric physeal closure, so true incidence is similar worldwide where physeal maturation is comparable.

Side-by-side guidance (no formal RCT-based guideline exists - recommendations are consensus/textbook-derived):

Counselling points (globally applicable):

• Explain that growth arrest is unlikely to be clinically significant because the patient is near skeletal maturity.
• Emphasise that the goal is articular congruity, and that displacement may be greater on CT than on plain films.
• Consent should cover the small risks of stiffness, superficial peroneal nerve irritation, and the possibility of converting a closed plan to open reduction.