Weight-bearing radiographs will be used to evaluate the stability of suprasyndesmotic ankle fractures. Patients with stable fractures will be randomised to operative or non-operative treatment.

Suprasyndesmotic fractures (Weber type C) are historically treated operatively because of the assumption that the distal tibiofibular syndesmosis is ruptured, leading to joint instability (Lauge-Hansen 1950, Boden 1989).

However, the medial deltoid ligament may function as the main stabiliser of the ankle joint by preventing external rotation of the talus and therefore maintains the dynamic congruity (Michelson 2007). Due to the stabilising effect of the deltoid ligament, an increasing number of transsyndesmotic fractures (Weber type B) are treated non-operatively with excellent results and without the burden of complications that accompany surgery (Gougoulias 2017, Mittal 2017, Bauer 1985).

The aims of the present study are to test the stability of suprasyndesmotic ankle fractures on weight-bearing radiographs and to evaluate the effect of non-operative versus operative treatment of stable suprasyndesmotic fractures.

The patients will have a weight-bearing (at least 50% of body weight) standing radiograph for the evaluation of the stability of the fracture. Patients with a congruent ankle mortise (i.e., stable fracture) on weight-bearing radiographs will be randomised to either operative (ORIF, reference treatment) or non-operative treatment (cast). Patients in both groups are allowed full weight-bearing.

Patients with an incongruent ankle mortise (i.e., unstable fracture) will be treated operatively according to current clinical practice and included in a parallel observational cohort study. Patients who are unwilling to participate in the intervention study are also invited to participate in the observational cohort study.

Inclusion Criteria:

• patients who present with a closed, isolated fibular fracture classified as suprasyndesmotic (Weber C) with a medial clear space of less than 7 mm in mortise view on primary radiographs.
• presentation less than 14 days after the injury.

Exclusion Criteria:

• previous fractures or ligamentous injury to the injured ankle.
• pathological fracture.
• diabetic neuropathy or other neuropathies.
• drug abuse.
• inability to consent and/or comply.
• inability to understand Norwegian language.
• inability to walk unaided prior to the fracture.
• patients with a concomitant tibial fracture requiring surgical treatment are excluded, but patients with undisplaced concomitant tibial fractures can be included.
• patients from outside the catchment area of the recruiting hospitals. However, they can be included if they are willing to undergo follow-up visits at one of the recruiting hospitals.

We have planned to use all the IPD only within the present study group.

Data will be plotted into a database by an independent blinded data manager.