Tillaux (SH-III) & Triplane (SH-IV) — Distal Tibial Transitional Fractures

Overview — Transitional Fractures of the Distal Tibia

Transitional fractures of the distal tibia are a unique group of physeal injuries that occur exclusively during the adolescent period when the distal tibial physis is undergoing asymmetric fusion. Because the medial portion of the distal tibial physis fuses before the lateral and anterolateral portions (the physis fuses from central → medial → anterolateral → posterolateral over approximately 18 months), there exists a critical window of vulnerability during which the unfused anterolateral portion of the physis is exposed to mechanical loading while the medial physis is already fused and therefore protected. This asymmetric fusion creates two specific fracture patterns: the Tillaux fracture (Salter-Harris Type III) and the triplane fracture (Salter-Harris Type IV) — both of which are impossible outside this narrow transition window of physeal closure (approximately ages 12–15 years).

The physeal fusion sequence of the distal tibia: the distal tibial physis does NOT fuse uniformly — it fuses in a specific, predictable sequence over approximately 18 months; the fusion order is: (1) central portion first; (2) medial (anteromedial) portion second; (3) anterolateral portion third (LAST to fuse); the anterolateral portion of the distal tibial physis is therefore the last portion to close; this `open anterolateral physeal window` explains why both Tillaux and triplane fractures involve the anterolateral corner of the distal tibia; the anterior tibiofibular ligament (AITFL) attaches to the anterolateral aspect of the tibial epiphysis — when the rest of the physis is fused but the anterolateral portion remains open, external rotation of the foot causes the AITFL to avulse the anterolateral epiphyseal fragment (Tillaux fracture)
Clinical context: both Tillaux and triplane fractures occur in late adolescence (12–15 years) when the physis is partially (but not fully) fused; they cannot occur before the partial fusion begins (the entire physis would fail uniformly rather than selectively) or after complete fusion (no physis remains); the mechanism for both injuries is typically external rotation of the foot/ankle, often in a sporting injury or a fall

Tillaux Fracture — Salter-Harris Type III

Feature	Detail
Classification	Salter-Harris Type III — the fracture line extends: (1) through the anterolateral portion of the PHYSIS (the only remaining unfused portion); (2) vertically through the epiphysis into the ankle joint (articular surface); the fragment that avulses is a piece of the anterolateral tibial epiphysis — it carries the AITFL attachment; the fracture is INTRA-ARTICULAR (the fracture line exits through the articular surface of the tibial plafond)
Mechanism	External rotation of the foot relative to the tibia; the AITFL is placed under tension; since the medial and central physis are fused but the anterolateral physis is still open, the AITFL avulses the anterolateral epiphyseal fragment at the unfused physeal level; the fragment is pulled anterolaterally by the AITFL
Radiological appearance	AP ankle X-ray: a vertical fracture line through the anterolateral tibial epiphysis is visible; the fragment is displaced anterolaterally; the fracture exits into the ankle joint articular surface; on the lateral view, the fracture may not be well-seen (the vertical fracture line is end-on in the AP plane); CT is the most important investigation for Tillaux fractures — it defines the exact articular displacement, the size of the fragment, and guides surgical planning; MRI can also delineate the cartilaginous component
Displacement assessment	The critical measurement is the articular step-off and gap at the ankle joint surface; >2 mm displacement = surgical indication; <2 mm = non-operative management; CT is the most accurate method for measuring articular displacement (plain X-ray significantly underestimates the true displacement)
Treatment	Undisplaced or <2 mm displacement: non-operative — above-knee cast in plantar flexion and internal rotation (reduces AITFL tension on the fragment) for 4–6 weeks; follow-up CT at 1 week to confirm no loss of position; Displaced (>2 mm articular step-off on CT): closed reduction under general anaesthesia (internal rotation of the foot reduces fragment displacement); if closed reduction achieves <2 mm → above-knee cast; if displacement >2 mm after closed reduction → ORIF; cannulated screw fixation (horizontal screw placed parallel to the tibial plafond, perpendicular to the fracture line, compressing the fragment — typically a 3.5 or 4.0 mm cannulated screw placed in the epiphysis without crossing the physis)

Triplane Fracture — Salter-Harris Type IV

Feature	Detail
Classification	Salter-Harris Type IV — the fracture has THREE components in THREE planes (hence `triplane`): (1) a SAGITTAL (vertical) fracture through the EPIPHYSIS into the ankle joint articular surface (seen on the AP X-ray — resembles a Tillaux); (2) a TRANSVERSE (horizontal) fracture through the PHYSIS (the unfused anterolateral physis); (3) a CORONAL (oblique/posterior-directed) fracture through the METAPHYSIS posteriorly (seen on the lateral X-ray — a posterior metaphyseal spike or fragment); the combination of all three creates a 2-part or 3-part fracture depending on the configuration
2-part vs 3-part triplane	2-part triplane: the entire posterolateral portion of the distal tibia (including epiphysis + posterior metaphyseal spike + lateral physeal component) avulses as a single large fragment; seen on AP view as a vertical epiphyseal fracture line (Tillaux component) and on lateral view as a posterior metaphyseal fragment; 3-part triplane: the fracture produces three separate fragments — the epiphysis (anterolateral), the posterior metaphyseal spike, and the intact medial distal tibia; the anterolateral epiphyseal fragment includes the Tillaux component; understanding 2-part vs 3-part is critical for surgical planning (3-part is more complex and may require separate fixation of the epiphyseal and metaphyseal components)
Radiological appearance	On plain X-ray: AP view — vertical fracture through the tibial epiphysis (Tillaux-like); Lateral view — posterior metaphyseal fragment (the spike or `Thurston-Holland equivalent`); however, the three-dimensional nature of the fracture is poorly appreciated on plain X-ray; CT scan is MANDATORY for all suspected triplane fractures — it precisely defines the fracture components, the degree of articular displacement, and the number of fragments; CT-based planning is essential before surgery
Treatment	Undisplaced or <2 mm articular displacement (on CT): non-operative — above-knee cast in plantar flexion and internal rotation; 4–6 weeks; follow-up CT to confirm position; Displaced (>2 mm articular step-off on CT): closed reduction under GA (internal rotation reduces the epiphyseal component); check residual displacement on CT post-reduction; if <2 mm after closed reduction → cast; if >2 mm → ORIF; surgical approach: the two fracture components (epiphyseal and metaphyseal) may be accessed through separate incisions (anteromedial for the epiphyseal component; posterolateral for the metaphyseal spike); cannulated screws for the epiphyseal component (parallel to the plafond — horizontal); a separate screw or lag screw for the posterior metaphyseal fragment; avoid crossing the physis with any fixation

Comparison — Tillaux vs Triplane

Feature	Tillaux Fracture	Triplane Fracture
Salter-Harris type	Type III (through physis + epiphysis)	Type IV (through metaphysis + physis + epiphysis — all three layers)
Fracture planes	2 planes (sagittal through epiphysis + transverse through physis)	3 planes (sagittal through epiphysis + transverse through physis + coronal through metaphysis)
Metaphyseal component	ABSENT — no metaphyseal fragment	PRESENT — posterior metaphyseal spike visible on lateral X-ray (`Thurston-Holland fragment` equivalent)
Best viewed on X-ray	AP view (vertical epiphyseal fracture line)	AP view (epiphyseal component) AND lateral view (metaphyseal component) — need BOTH views + CT
CT importance	Essential for measuring articular displacement accurately (plain X-ray underestimates)	MANDATORY — the only way to understand the complex 3D anatomy of the fracture; guides surgical planning for 2-part vs 3-part patterns
Age	Slightly OLDER adolescents (12–15 years, closer to skeletal maturity — less physis remaining when the Tillaux avulsion occurs)	Slightly YOUNGER adolescents (10–14 years — more physis still open when triplane occurs, allowing the metaphyseal component to form)
Fixation	Single horizontal cannulated screw in the epiphysis (parallel to the plafond)	Two screws (epiphyseal component horizontally + metaphyseal component separately); 2-part may be reducible with a single screw through the epiphysis that also captures the metaphyseal fragment

Exam Pearls

Distal tibial physis fusion order: central → medial → anterolateral (LAST); the anterolateral physeal `window` is exposed during transitional period → Tillaux (SH-III) and triplane (SH-IV) fractures; only possible during the 18-month transition window of physeal closure (approx. 12–15 years)
Tillaux fracture: SH-III; AITFL avulses the anterolateral epiphyseal fragment; 2 planes (sagittal + transverse); NO metaphyseal component; best on AP view; CT to measure articular displacement; >2 mm = ORIF; horizontal screw in epiphysis
Triplane fracture: SH-IV; 3 planes (sagittal epiphysis + transverse physis + coronal metaphysis); posterior metaphyseal spike on lateral X-ray is the KEY distinguishing feature from Tillaux; CT mandatory; 2-part vs 3-part; >2 mm = ORIF
The distinguishing plain X-ray feature: Tillaux — no metaphyseal fragment (pure epiphyseal + physeal injury); triplane — posterior metaphyseal spike visible on lateral view (`Thurston-Holland equivalent`); if you see a posterior metaphyseal spike on the lateral ankle X-ray in an adolescent → triplane, not Tillaux
Both require CT: plain X-ray UNDERESTIMATES articular displacement in both fracture types; CT is mandatory for all suspected transitional fractures before any management decision; the surgical threshold is >2 mm articular step-off on CT (not plain X-ray)
Reduction technique: internal rotation of the foot reduces both the Tillaux and the epiphyseal component of the triplane; plantar flexion relaxes the AITFL; immobilise in cast in plantar flexion + internal rotation if reduction achieved
Growth disturbance risk: both fractures involve only the residual open anterolateral physis; the central and medial physis are already fused; growth arrest risk is low compared to younger physeal injuries; the primary concern is articular incongruency and post-traumatic ankle OA
Post-traumatic OA: the major long-term risk with articular incongruency (>2 mm step-off); anatomical reduction and fixation minimises this risk; outcome correlates directly with quality of articular restoration

Tillaux (SH-III) & Triplane (SH-IV) — Distal Tibial Transitional Fractures

References

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