The investigators will conduct a prospective cohort study on the use of weight-bearing radiographs to evaluate stability in ankles with isolated, trans-syndesmotic (Weber type B) fibular fractures. Stable fractures will be treated conservatively using a functional brace, unstable fractures will undergo surgical fixation.

It is widely accepted that fractures in stable ankles can be treated non-operatively and fractures in unstable ankles needs internal fixation surgery (Michelson, Magid & McHale, 2007, Gougoulias, Khanna, Seellariou, Maffulli, 2010). Clinical decision-making is thus based on ankle stability evaluation. The integrity of medial structures, mainly the deep deltoid ligament, is considered the most important determinant for stability of the ankle mortise (Michelson, Magid & McHale, 2007, Gougoulias, Khanna, Seellariou, Maffulli, 2010). Weber B fractures, with no obvious sign of medial side injury on initial plain radiographs, have to be considered of uncertain stability until adequate stress testing is performed.

Currently there is no definite consensus on what test(s) best determines stability in ankles with undisplaced, isolated lateral malleolar fractures. Much used methods comprises manual stress radiographs and gravity stress radiographs (McConnel, Creevy & Tornetta, 2004). However recent studies have shown that such methods overestimate the need for surgical fixation indicating the need for a different method to make up the basis for surgical indication (Dawe, Shafafy, Quayle, Gougoulias, Wee & Sakellariou, 2015, Hastie, Akhtar, Butt, Baumann & Barrie, 2015, Holmes, Acker, Murphy, McKinney, Kadakia & Irwin, 2016, Hoshino, Nomoto, Norheim & Harris, 2012, Koval, Egol, Cheung, Goodwin & Spratt (2007), Seidel et al., 2017, Weber, Burmeister, Flueckiger & Krause, 2010). Authors of recent studies have proposed weightbearing radiographs as an alternative method to distinguish stable and unstable fractures, significantly reducing the need for operative treatment (Dawe et al., 2015, Hastie et al., 2015, Hoshino et al, 2012, Holmes et al., 2016, Seidel et al., 2017, Weber et al. 2010).

To evaluate weight-bearing radiographs ability to determine stability our primary focus is to evaluate if conservative treatment for "gravity unstable/weightbearing stable" ankles produces different outcomes than conservative treatment for "gravity stable/weightbearing stable" ankles.

Participants will be assigned to non-operative or surgical treatment based on ankle stability evaluation using results from weightbearing radiographs consistently. Stable ankles will be treated non-operatively with a functional brace (AirCast) for 6 weeks. Participants will be instructed to bear weight as tolerated and to actively do standardized range-of-motion exercises. Standard operative treatment is open reduction and internal fixation of the fracture using plate and screws.

Inclusion Criteria:

• Isolated Weber type B fractures without radiological signs of medial clear space widening on initial radiographs. Patients must be 18-80 years of age. Before the injury patients should be mobilized without walking aids. They should be compliant with good communication skills in the Norwegian or English languages. Patients must live in Østfold or nearby areas so they are able to meet to follow-up consultations.

Exclusion Criteria:

• Patients presenting with any of the following will be excluded from the study: Fracture of the medial malleolus. Information about prehospital fracture closed reduction. Open fracture. Fracture resulting from high-energy trauma or multi-trauma. Pathologic fracture. Diabetes Mellitus type 1 and 2. Neuropathies. Cognitive disorders. Previous history of ankle fracture. Previous history of ankle-/foot surgery. Generalized joint disease such as RA. Patients with insufficient Norwegian or English language proficiency or lack of communication skills.