Ankle fractures occur in 1 out of 800 persons a year and is a common injury. The deltoid ligament is necessary for the stability of the joint and guides choice of treatment. Cadaveric studies have shown that deltoid ligament repair gives more stability than the osteosynthesis of the lateral malleolus itself. The investigators want to show if suture of the deltoid ligament in unstable ankle fractures contribute to a better functional result and/or prevent long term osteoarthritis for our participants. Patients sustaining severe ankle fractures have shown a considerable loss of function that might affect their long term activities of daily living (ADL) function. Improving outcome for this group may preserve some patients' ability to work and reduce community expenses.

During the last two decades less severe ankle fractures have been shown not to need operative treatment in general. The total number of ankle fracture surgeries has gone down. Therefore, surgically treated ankle fractures nowadays are on average more complex. The understanding of these injuries implies a recognition of the role of the deep deltoid ligament as a main stabilizer of the ankle joint. Deltoid ligament repair is documented to be a good option to regain ankle joint anatomy from smaller studies. This repair also compensates for syndesmotic injury to some extent. The effect of deep deltoid ligament repair in Weber B ankle fractures and its effect on long term function and arthritis is not yet known from clinical studies.

The investigators aim to show whether deltoid ligament suture gives a clinically significant superior result than solely osteosynthesis of the lateral malleolus in unstable ankle fractures. This will be performed as a multicentre randomized controlled study.

Inclusion criteria; fluent in oral and written Norwegian language

• isolated Weber type B fractures and Weber B+ posterior malleolar Mason Molloy class I.
• Initial medial clear space (MCS)>=7mm or weightbearing x-ray evaluated as unstable or primary reposition after fracture dislocation.
• Pre-injury walking ability without aids.

Exclusion criteria

• assumed not compliant (drug use, cognitive- and/or psychiatric disorders).
• previous history of ipsilateral ankle fracture or ipsilateral major ankle-/foot surgery.
• open fx Gustilo Anderson II or more, multi-trauma and pathologic fracture.
• neuropathies and generalized joint disease such as Rheumatoid Arthritis or other more severe condition in same extremity
• fixation of tibial fragment or syndesmotic screw or suture button planned prior to surgery