The Weber system describes three types of ankle fracture. Danis and Weber based their classification on the involvement of the fibula, which they regarded as being the key to ankle stabilty:
- type A - the fibula is fractured below the tibio-fibular syndesmosis, as a result of abduction or adduction. The medial malleolus may be fractured or the deltoid ligament torn; however these fractures are stable after reduction.
- type B - fractures result from external rotation, and are oblique fractures running upwards from the joint line. The syndesmosis is intact and the mortise not disturbed. The medial structures usually are disturbed.
- type C - unstable fractures above the syndesmosis resulting from abduction alone or from abduction with external rotation. The syndesmosis ruptures (as may the interosseous membrane), the fibula may become tilted and the mortise widened.