4. Weber Classification of Distal Fibula Fractures
Why the Syndesmosis Is the Reference Line
The Weber classification (also called the Danis–Weber classification) sorts distal fibula fractures by a single geometric question: where does the fracture line sit relative to the distal tibiofibular syndesmosis? The syndesmosis is the fibrous joint between the distal tibia and fibula, anchored by the anterior inferior tibiofibular ligament (AITFL), posterior inferior tibiofibular ligament (PITFL), interosseous ligament, and the transverse ligament. Its distal margin — the level of the tibial plafond — is the practical reference line on radiographs.
The classification matters because it predicts the mechanism and, more importantly, the stability of the ankle mortise. A fracture below the syndesmosis leaves the tibiofibular link intact; a fracture above it implies the syndesmosis has been disrupted (or must be assumed disrupted until proven otherwise). That distinction drives whether the patient needs a syndesmotic screw or tightrope fixation in addition to fibular fixation.
Weber divides fractures into three types:
- Weber A — fracture line below the level of the tibial plafond (infra-syndesmotic). Typically an avulsion of the lateral malleolus by the lateral collateral ligaments, often from an inversion injury. The syndesmosis is intact.
- Weber B — fracture line at the level of the plafond (trans-syndesmotic), usually beginning at the joint line and extending proximally and posteriorly. The syndesmosis may be partially injured; stability depends on the fracture pattern and the integrity of the AITFL.
- Weber C — fracture line above the plafond (supra-syndesmotic). The syndesmosis is disrupted by definition, and the injury is unstable.
Reading the Mortise and Lateral Views Together
Weber classification is a two-view exercise. The mortise view (AP with the leg internally rotated ~15–20°, so the malleoli are seen in profile without overlap) shows the fracture level relative to the plafond and reveals any widening of the medial clear space or tibiofibular clear space. The lateral view confirms the fracture's proximal extent, shows posterior malleolar involvement, and — critically — lets you trace the fracture line's true course, which is often oblique and can appear higher or lower than it does on the mortise view.
Two practical rules keep the classification honest:
- Use the highest point of the fracture line where it crosses the lateral cortex, not the lowest. An oblique Weber B fracture that starts at the joint line and runs proximally is still classified by its relationship to the plafond at the point where it exits the fibula.
- When the fracture straddles the line, classify by the dominant pattern and note the ambiguity. A fracture beginning at the plafond and extending well above it is a Weber B with a high extension; a fracture entirely above the plafond is Weber C. Do not force a borderline case into a type without documenting why.
Worked Classification of a Case Series
Below is a representative teaching series of five distal fibula fractures, each described by its mortise and lateral findings. The classification column shows how the two views combine to assign a Weber type. These are illustrative examples constructed for practice, not measured patient data.
| Case | Mortise view finding | Lateral view finding | Syndesmosis status | Weber type |
|---|---|---|---|---|
| 1 | Transverse fracture of lateral malleolus, line entirely below plafond | Avulsion fragment at tip of fibula | Intact; medial clear space normal | A |
| 2 | Oblique fracture beginning at plafond, extending proximally | Line runs posterosuperiorly, exits above plafond | Clear space 4 mm; equivocal | B (borderline) |
| 3 | Oblique fracture at plafond with 2 mm lateral shift | Posterior malleolus intact; line at joint level | Clear space 3 mm; stable | B |
| 4 | Fracture line above plafond, fibula shortened | Comminuted supra-syndesmotic fracture | Clear space 7 mm; widened | C |
| 5 | High fibular fracture with medial clear space 6 mm | Fracture well above plafond; deltoid ligament injury implied | Disrupted; unstable mortise | C |
Case 2 is the instructive one. On the mortise view alone the fracture appears to start at the plafond, which suggests Weber B. The lateral view shows the line exiting the fibula above the plafond, and the tibiofibular clear space is at the upper limit of normal. The correct call is Weber B with a high extension and a note that syndesmotic injury cannot be excluded — which is exactly the kind of borderline case that changes surgical planning.
Visualizing the Classification Logic
The diagram below maps the decision path from the two radiographic views to the Weber type, including the syndesmotic stability check that separates a stable Weber B from one requiring fixation.
Documenting the Classification
A Weber type alone is not a complete radiographic report. The classification should be paired with the findings that justify it, so a colleague or surgeon can verify the call. A practical documentation template for each case in the series:
| Field | What to record | Example entry |
|---|---|---|
| Fracture level | Below / at / above plafond, with the view used | At plafond on mortise; exits above on lateral |
| Fracture pattern | Transverse, oblique, spiral, comminuted | Oblique, posterosuperior |
| Displacement | Millimeters of lateral shift or shortening | 2 mm lateral shift |
| Tibiofibular clear space | Measured on mortise view | 4 mm (upper limit normal) |
| Medial clear space | Measured on mortise view | 3 mm |
| Posterior malleolus | Intact / involved, size | Intact |
| Weber type | A / B / C, with qualifier if borderline | B, high extension, syndesmosis equivocal |
Common Pitfalls and How to Catch Them
- Classifying by the lowest point of an oblique fracture. An oblique Weber B fracture that begins at the plafond and runs proximally will look "at the plafond" at its distal end but "above" at its proximal end. Use the exit point on the lateral cortex and note the extension.
- Missing a high fibular fracture. A Weber C fracture can sit several centimeters above the plafond and be partially off the bottom of a tightly collimated film. Always include the full fibula on at least one view when a medial clear space widening is present.
- Calling a Weber B stable without measuring. A Weber B with a tibiofibular clear space of 5–6 mm and a medial clear space of 4–5 mm is functionally unstable even though the fracture line is at the plafond. Measure both spaces and document them.
- Ignoring the posterior malleolus. A posterior malleolar fracture fragment larger than ~25–30% of the articular surface changes fixation planning regardless of Weber type; record its size on the lateral view.
The Weber system is deliberately simple — one reference line, three categories — and that simplicity is its strength. Applied consistently across a case series, with the mortise and lateral views read together and the syndesmotic measurements recorded alongside the type, it gives a reproducible, surgically meaningful classification that a trainee can apply and a reviewer can audit.