Residency · Residency · Orthopedic Surgery
Ankle Fractures: Weber Classification and Syndesmotic Injury
Introduction
Ankle fractures are among the most common injuries treated by orthopedic surgeons, with an incidence of approximately 187 per 100,000 persons per year. Accurate classification, recognition of associated ligamentous injuries (particularly syndesmotic disruption), and appropriate treatment selection are essential for restoring ankle stability and preventing post-traumatic arthritis.
Anatomy
The ankle mortise is formed by the tibial plafond, medial malleolus, and lateral malleolus (distal fibula). Stability depends on the bony architecture and three ligament complexes. The lateral collateral ligaments consist of the anterior talofibular ligament (ATFL), calcaneofibular ligament (CFL), and posterior talofibular ligament (PTFL). The deltoid ligament on the medial side has superficial and deep components, with the deep deltoid serving as the primary restraint to lateral talar shift. The syndesmosis comprises the anterior inferior tibiofibular ligament (AITFL), posterior inferior tibiofibular ligament (PITFL), interosseous ligament (IOL), and interosseous membrane. The fibula bears approximately 6 to 16% of axial load and is critical for maintaining ankle stability.
Classification Systems
Danis-Weber Classification
| Type | Fibula Fracture Level | Syndesmosis | Stability | Typical Treatment |
|---|---|---|---|---|
| A | Below syndesmosis (infrasyndesmotic) | Intact | Stable | Nonoperative (unless unstable variant) |
| B | At syndesmosis (transsyndesmotic) | Partial disruption possible | Variable (depends on deltoid) | Stress test to determine; ORIF if unstable |
| C | Above syndesmosis (suprasyndesmotic) | Disrupted | Unstable | ORIF + syndesmotic fixation |
The Danis-Weber classification is based on the level of the fibular fracture relative to the syndesmosis. Type A fractures occur below the syndesmosis (infrasyndesmotic), typically representing an avulsion of the lateral malleolus tip from a supination-adduction mechanism. The syndesmosis is intact and the ankle is inherently stable, so treatment is usually nonoperative unless there is a vertical medial malleolus fracture creating an unstable variant.
Type B fractures occur at the level of the syndesmosis (transsyndesmotic) and are the most common type, comprising approximately 60 to 70% of ankle fractures. The AITFL may be partially disrupted while the interosseous membrane remains intact. Stability depends on the integrity of the deltoid ligament and the syndesmosis, with stable patterns treated nonoperatively and unstable patterns requiring fixation.
Type C fractures occur above the syndesmosis (suprasyndesmotic). The syndesmosis is disrupted and the interosseous membrane is torn to the level of the fracture, making these inherently unstable and requiring surgical fixation. This category includes the Maisonneuve fracture, a proximal fibula fracture with complete syndesmotic and interosseous membrane disruption.
Lauge-Hansen Classification
The Lauge-Hansen classification describes the mechanism of injury based on foot position (first word) and direction of force (second word). Supination-adduction injuries produce a lateral ligament injury or transverse fibula fracture below the syndesmosis, followed by a vertical medial malleolus fracture. Supination-external rotation is the most common mechanism and causes sequential injury to the AITFL, a spiral fibula fracture at the syndesmosis, the PITFL or posterior malleolus, and then the deltoid. Pronation-abduction results in deltoid injury followed by a comminuted fibula fracture at or above the syndesmosis. Pronation-external rotation produces deltoid injury, AITFL disruption, a spiral fibula fracture above the syndesmosis, and then PITFL disruption.
Clinical Assessment
Evaluation includes assessment of swelling, deformity, skin tenting, and open wounds. The proximal fibula must be palpated to exclude a Maisonneuve injury, and the entire length of the fibula should be examined. The deltoid ligament region is assessed for tenderness and ecchymosis indicating medial clear space widening. A neurovascular examination of the dorsalis pedis and posterior tibial pulses along with sensation is performed. Compartment syndrome of the foot or leg should be considered in high-energy injuries.
Imaging
Radiography
AP, lateral, and mortise (15 to 20 degrees internal rotation) views of the ankle are standard. On the mortise view, the medial clear space (distance between the medial malleolus and talus) should be less than 4 mm, as widening indicates deltoid injury. The tibiofibular clear space, measured 1 cm above the plafond on the AP view, should be less than 6 mm. The tibiofibular overlap should be greater than 6 mm on the AP view or greater than 1 mm on the mortise view. Talar tilt, defined as asymmetry of the superior joint space, indicates instability. Full-length tibia and fibula radiographs are obtained if a Maisonneuve injury is suspected. Gravity or external rotation stress views assess deltoid competence in isolated Weber B fractures without obvious medial injury.
Advanced Imaging
CT scanning is useful for posterior malleolus fractures to assess size and articular involvement, for complex fracture patterns, and for syndesmotic assessment. MRI evaluates ligamentous integrity of the deltoid and syndesmosis when clinical and radiographic findings are equivocal. Weightbearing CT is an emerging modality for assessing syndesmotic stability and reduction quality.
Syndesmotic Injury
Importance
Syndesmotic disruption leads to widening of the ankle mortise and lateral talar shift. Even 1 mm of talar lateral shift reduces tibiotalar contact area by 42%, dramatically increasing contact pressures and arthritis risk. Syndesmotic injury must be suspected in all Weber B and C fractures.
Intraoperative Assessment
The Cotton test applies lateral traction on the fibula with a bone hook under fluoroscopy, with greater than 3 to 4 mm of widening indicating instability. The external rotation stress test applies external rotation torque under fluoroscopy to assess for medial clear space widening.
Fixation Techniques
Syndesmotic screws of 3.5 or 4.5 mm are placed 2 to 4 cm above the plafond engaging 3 or 4 cortices, with 1 to 2 screws typically used. Suture button devices such as the TightRope allow physiologic motion at the syndesmosis and may offer advantages in maintaining reduction while eliminating the need for screw removal. Screws are either removed at 3 to 4 months or left in place if asymptomatic, though routine removal remains debated. Anatomic reduction of the fibula in the incisura is critical, as malreduction of the syndesmosis is a common cause of poor outcomes.
Treatment
Nonoperative
Nonoperative management is indicated for stable fracture patterns, including isolated lateral malleolus fractures without medial tenderness or mortise widening, and isolated medial malleolus fractures with intact lateral structures. Treatment involves a short leg cast or functional brace (CAM boot) with progressive weight-bearing and close radiographic follow-up to ensure no displacement occurs.
Operative
Lateral malleolus fixation is performed with a one-third tubular plate, anatomic plate, or lag screw. Medial malleolus fixation uses two partially threaded cancellous screws or tension band wiring. Posterior malleolus fixation is recommended if the fragment involves greater than 25 to 33% of the articular surface or if it contributes to syndesmotic instability, and it can be fixed with anterior-to-posterior screws or a posterior antiglide plate. The syndesmosis is fixed as described above after all malleolar fractures are stabilized.
Posterior Malleolus Considerations
Recent evidence suggests that direct fixation of the posterior malleolus via a posterolateral approach may restore syndesmotic stability and eliminate the need for separate syndesmotic fixation in many cases. CT scanning is essential for preoperative planning of posterior malleolus fractures.
Clinical Pearls
The proximal fibula should always be palpated in any ankle injury, as a Maisonneuve fracture (proximal fibula fracture with complete syndesmotic disruption) is commonly missed and requires syndesmotic fixation. Even 1 mm of persistent lateral talar shift significantly increases contact pressures and the risk of post-traumatic arthritis, making anatomic reduction of the mortise the single most important goal. Stress radiographs are essential to assess deltoid competence in Weber B fractures without obvious medial injury, with medial clear space widening greater than 4 mm indicating instability requiring surgery. Anatomic reduction of the fibula within the incisura is critical during syndesmotic fixation, as malreduction is a leading cause of poor outcomes and is best assessed with intraoperative CT when available.
References
- Ramsey PL, Hamilton W. Changes in tibiotalar area of contact caused by lateral talar shift. J Bone Joint Surg Am. 1976;58(3):356-357.
- Michelson JD. Ankle fractures resulting from rotational injuries. J Am Acad Orthop Surg. 2003;11(6):403-412.
- Sagi HC, Shah AR, Sanders RW. The functional consequence of syndesmotic joint malreduction at a minimum 2-year follow-up. J Orthop Trauma. 2012;26(7):439-443.
- Tornetta P III, Axelrad TW, Sibai TA, Creevy WR. Treatment of the stress positive ligamentous SE4 ankle fracture: incidence of syndesmotic trans-fixation and a clinical decision rule. J Orthop Trauma. 2012;26(11):659-661.