Danis–Weber Classification — Ankle (Fibula Level)

Overview — Ankle Fracture Classification

The Danis-Weber classification (described by Robert Danis in 1949 and refined by Bernhard Georg Weber in 1966) is the most widely used system for classifying ankle fractures in clinical practice. It is based solely on the LEVEL of the fibular fracture relative to the ankle mortise (the syndesmosis level), which correlates with the degree of instability, the likelihood of syndesmotic injury, and the indication for operative versus non-operative management. Although it does not address the medial side or the posterior malleolus, its simplicity, reproducibility, and direct treatment implications make it the most practical ankle fracture classification in clinical use. It is complementary to the Lauge-Hansen classification (which describes mechanism).

The ankle mortise: the tibiotalar articulation is a mortise-and-tenon joint; the mortise is formed by the distal tibia (the `plafond`) superiorly and the medial malleolus medially + the lateral malleolus (distal fibula) laterally; the talus fits precisely within this mortise; the entire ankle joint depends on the integrity of the mortise — even 1 mm of talar shift dramatically increases tibiotalar contact stress; the tibiofibular syndesmosis (the strong ligamentous complex connecting the distal tibia and fibula — consisting of the anterior inferior tibiofibular ligament [AITFL], posterior inferior tibiofibular ligament [PITFL], and the interosseous ligament/membrane) maintains the fibula in its proper lateral position within the mortise
Why fibular fracture level matters: the level of the fibular fracture relative to the syndesmosis determines whether the syndesmotic ligaments are intact; a fracture BELOW the syndesmosis (Weber A) typically does not disrupt the syndesmosis; a fracture AT the level of the syndesmosis (Weber B) may or may not disrupt it; a fracture ABOVE the syndesmosis (Weber C) by definition disrupts the entire syndesmotic complex; syndesmotic disruption = ankle mortise widening = talar instability = surgical indication

Danis-Weber Classification

Weber Type	Fibular Fracture Level	Syndesmosis Status	Mechanism (Lauge-Hansen)	Stability	Treatment
Weber A — Infrasyndesmotic	Below the level of the syndesmosis — the fibular fracture is BELOW (distal to) the tibial plafond / the joint line of the ankle; the fracture is within or below the ankle mortise level; typically a transverse avulsion fracture of the tip of the lateral malleolus	INTACT — the syndesmotic ligaments (AITFL, PITFL, interosseous membrane) are completely INTACT; the fibular fracture is below the level at which the syndesmosis attaches; no tibiofibular diastasis possible	Supination-Adduction (SA) — Type 1 (Lauge-Hansen): the foot supinates and the talus adducts; the lateral malleolus is avulsed transversely by the lateral collateral ligament	STABLE — no syndesmotic disruption; the ankle mortise is stable; the talus cannot shift laterally because the syndesmosis and the tibiofibular relationship are intact; even if the medial side is also injured, the lateral stabiliser (fibula) is not compromised above the joint level	Non-operative in the vast majority — below-knee cast or walking boot for 4–6 weeks; weight-bearing as tolerated; the vast majority of Weber A fractures are stable and do NOT require ORIF; ORIF only if: (1) associated medial malleolus fracture with significant displacement (bimalleolar equivalent), (2) large fragment with intra-articular step, or (3) rare cases of very active patients needing early return to sport
Weber B — Transsyndesmotic	AT the level of the syndesmosis — the fibular fracture runs obliquely or spirally at or through the level of the tibial plafond / ankle joint line; the fracture typically begins at the level of the joint line anteriorly and runs proximally and posteriorly (the classic supination-external rotation oblique fracture of the fibula)	VARIABLE — may be intact or disrupted depending on the injury severity; the fibular fracture is at the level of the AITFL attachment; in lower-energy injuries (SER Type 2), the AITFL may be intact (or avulse a small bony fragment from the fibula — the `Chaput` fragment or from the tibia — the `Wagstaffe` fragment); in higher-energy injuries (SER Type 3-4), the AITFL is torn and the syndesmosis is disrupted; STABILITY ASSESSMENT IS MANDATORY for all Weber B fractures	Supination-External Rotation (SER) — the most common ankle fracture mechanism; the foot is in supination, the talus externally rotates within the mortise; progressive ligamentous injury from anterior to posterior	VARIABLE — may be stable (AITFL intact) or unstable (AITFL torn + deltoid/medial malleolus disrupted = `bimalleolar` or `bimalleolar equivalent`); the isolated lateral malleolus Weber B fracture with intact medial structures = STABLE = non-operative; the same fracture with disrupted medial side = UNSTABLE = operative; clinical assessment of medial side + stress examination (manual stress or gravity stress test) determines stability	Depends on stability assessment: STABLE Weber B (isolated lateral malleolus, intact medial side, <3 mm displacement) → non-operative (below-knee cast or boot for 6 weeks); UNSTABLE Weber B (bimalleolar, medial tenderness + stress positive, >3 mm displacement) → ORIF (fibular plate + lag screw + medial malleolus screw); syndesmosis assessment and fixation if positive intraoperative stress testing (Cotton test or external rotation stress test under fluoroscopy)
Weber C — Suprasyndesmotic	ABOVE the level of the syndesmosis — the fibular fracture is ABOVE (proximal to) the tibial plafond; the fracture is above the ankle joint level; the fibula may fracture anywhere from just above the syndesmosis (distal Weber C) to the fibular neck (Maisonneuve fracture — the most proximal variant)	DISRUPTED — by definition, a fibular fracture above the syndesmosis has torn the ENTIRE interosseous membrane from the ankle level up to the fibular fracture; the syndesmosis is completely disrupted; the AITFL, interosseous ligament, and PITFL are all torn; the tibiofibular relationship is lost; this always produces a widened ankle mortise if the medial side also fails	Pronation-Abduction (PA) or Pronation-External Rotation (PER) — the foot pronates; the talus abducts or externally rotates; the medial side fails first, then the syndesmosis tears from distal to proximal, finally fracturing the fibula above the syndesmosis	UNSTABLE — the syndesmosis is always disrupted; the fibula is fractured above the mortise; without fixation, the talus will shift laterally within the mortise (talar shift); however, whether the ankle mortise is CURRENTLY WIDENED depends on the medial side: if the deltoid ligament/medial malleolus is also disrupted, the mortise is widened; if the medial side is intact (rare), the mortise may still be concentrically reduced but is at risk	OPERATIVE — fibular fixation (plate and screws for fibular fracture) + syndesmotic fixation (one or two syndesmotic screws or suture-button [TightRope] device through 3 or 4 cortices) + medial malleolus fixation if fractured; Maisonneuve fractures (proximal fibular fracture — the fibula need NOT be plated) → medial malleolus/deltoid fixation + syndesmotic screws; the Maisonneuve is the most commonly missed variant (proximal fibular fracture + medial ankle injury + widened ankle mortise)

Stability Assessment for Weber B Fractures

The medial side assessment: the single most important determinant of Weber B ankle fracture stability is the MEDIAL SIDE; if the medial structures (deltoid ligament + medial malleolus) are intact, an isolated fibular Weber B fracture is STABLE and can be treated non-operatively; if the medial side is disrupted (either medial malleolus fracture or deltoid ligament tear), the ankle mortise is rotationally unstable → operative fixation; clinical assessment: medial ankle tenderness over the deltoid ligament (or the medial malleolus) in a Weber B fracture with no visible medial fracture = bimalleolar equivalent = unstable = treat operatively
Gravity stress test: the single most practical test for medial stability in an isolated Weber B fracture; the patient is positioned laterally (injured side up) with the ankle hanging free; a standard mortise ankle X-ray is taken WITHOUT manual stress applied; if the medial clear space widens >4 mm (or >1 mm more than the superior clear space on the mortise view) under gravity alone → positive → deltoid disruption → unstable ankle → operative; a non-widened medial clear space under gravity stress confirms intact deltoid → stable → non-operative management is appropriate
The `Sorbonne criteria` for non-operative Weber B: (1) isolated lateral malleolus fracture; (2) medial clear space ≤4 mm on gravity stress views; (3) less than 3 mm fibular displacement; (4) no articular step-off; all four criteria met = stable = non-operative management is appropriate and outcomes are equivalent to operative management

Maisonneuve Fracture — The Important Special Case

Maisonneuve fracture: a proximal fibular fracture (at or near the fibular neck — the highest Weber C variant) combined with ankle mortise disruption from below; the entire interosseous membrane is torn from the ankle mortise level up to the proximal fibular fracture level; clinically: the patient presents with ankle pain (medial > lateral) and a wide mortise on X-ray — but no fibular fracture is visible on the ankle X-rays (because the fracture is at the fibular neck, not included in ankle views); examination: proximal fibular tenderness in a patient with ankle injury = Maisonneuve until proven otherwise; management: the proximal fibular fracture itself does NOT require fixation (the fibula heals readily in this location); treatment = medial malleolus fixation (if fractured) OR deltoid repair + syndesmotic fixation (one or two syndesmotic screws or TightRope)

Exam Pearls

Danis-Weber: A = below syndesmosis (stable, non-op); B = at syndesmosis (variable stability — assess medial side); C = above syndesmosis (syndesmosis disrupted, operative); based solely on fibular fracture level relative to ankle joint/syndesmosis
Weber B stability = medial side: intact medial structures = stable = non-op; disrupted medial (fracture or deltoid tear) = bimalleolar equivalent = unstable = operative; gravity stress test is the key investigation; medial clear space >4 mm = positive = unstable
Weber C = always disrupted syndesmosis: fibula above joint = entire interosseous membrane torn to the level of the fracture; syndesmotic fixation mandatory (syndesmotic screw or TightRope through 3 or 4 cortices); the fibula must be plated for distal/mid-fibular Weber C; Maisonneuve (proximal) need NOT plate the fibula
Maisonneuve fracture: proximal fibular fracture + ankle disruption; easily missed (fibula not on ankle views); examine the whole fibula in all ankle injuries; treat medial + syndesmosis, NOT the proximal fibula
Talar shift: even 1 mm lateral talar shift reduces tibiotalar contact area dramatically (by ~42%) → rapidly increases contact stress → post-traumatic ankle OA; this is why anatomical reduction of the ankle mortise is mandatory; the goal of ankle fracture fixation is to maintain a concentrically reduced mortise
Bimalleolar equivalent fracture: Weber B fibular fracture + medial clear space widening (no medial bony fracture, but deltoid is torn); the medial injury is ligamentous, not bony; the ankle is as unstable as a true bimalleolar fracture; requires ORIF (lateral plate + syndesmotic fixation if positive stress test)
Operative vs non-op for isolated Weber B: the AIRCAST trial and UKFOOT trial demonstrated that functional bracing gives equivalent 6-week outcomes to operative fixation for isolated Weber B fractures in appropriately selected stable ankles; gravity stress test is the key selection tool; unstable ankles still require ORIF

Danis–Weber Classification — Ankle (Fibula Level)

References

Share Wiki