Prospective cohort study to evaluate the use of a NanoScopic procedure to assess deltoid ligament injuries with outcomes measured at baseline, 6 weeks, 12 weeks, 1 year and 2 years. Further to examine whether the findings correlate with results on gravity stress test and weightbearing radiographs.

Purpose and research question The main purpose is to evaluate integrity in the deep deltoid ligament in ankles with isolated Weber type B fractures using a minimally invasive Nanoscopic technique. Further results of a Nanoscopic evaluation will be correlated to the results of gravity stress and weightbearing radiographs. Additionally, the Nanoscopic evaluation will be used to assess associated injuries including cartilage and syndesmotic lesions.

Methods Primary evaluation will be done in the acute setting. All isolated Weber type B fractures without radiological signs of instability (medial clear space of 7 mm or less) on initial non-weightbearing radiographs presenting to our clinic will be evaluated for inclusion. Nanoscopic evaluation will determine stability for all patients with radiographic measurements indicating "uncertain stability". "Uncertain stability" of the ankle is assumed when at least one out of 3 (plain-, gravity- or weightbearing-) radiographs is showing instability. Like Seidel et al. (2017), in the event of a MCS of over 7 mm on initial non-weightbearing radiographs the ankle is considered unstable and will be evaluated for surgery. These patients will not be evaluated for inclusion.

For radiographic tests the size of the MCS will make up an indirect measurement of deltoid ligament capacity. The MCS is defined as the distance between the medial border of the talus and the lateral border of the medial malleolus on a line parallel to and 5 mm below the talar dome on anteroposterior radiographs. A MCS of 5 mm or less defines the ankle as stable. An MCS >5 mm AND 1 mm or more increase compared to the contralateral (non-injured ankle) ankle defines the ankle as unstable.

Plain-, weightbearing- and gravity stress radiographs and nanoscopic evaluation will be done 3-14 days after injury at the outpatient clinic. The radiographic test battery will be done prior to nanoscopy. Only patients demonstrating at least one positive stress radiograph (weightbearing or gravity) or a plain radiograph with a MCS measurement above the threshold (5 mm AND 1 mm or more increase compared to the contralateral ankle) will undergo nanoscopic evaluation.

Participants with "uncertain" stability will be assigned to non-operative or surgical treatment based on ankle stability evaluation using results from the NanoScopic evaluation consistently. Stability is assumed when the posterior part of the deep deltoid ligament is visible and intact. 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. Unstable ankles will be operated on. Standard operative treatment is open reduction and internal fixation of the fracture using plate and screws. The goal is an osteosynthesis that allow for early range-of-motion exercises, but weightbearing is usually not tolerated until 6 weeks postoperatively.

Inclusion Criteria:

Patients:

• With isolated Weber type B fractures without radiological signs of medial clear space widening on initial plain radiographs (MCS < 7mm).
• Demonstrating at least one positive stress radiograph (weightbearing or gravity) or a plain radiograph with a MCS measurement above the threshold (5 mm AND 1 mm or more increase compared to the contralateral ankle) (WP2).
• 18-80 years of age.
• With pre-injury walking ability without aids.

Exclusion Criteria:

Patients:

• With fracture of the medial malleolus, pre-hospital closed fracture reduction, open fracture, fracture resulting from high-energy trauma or multi-trauma and pathologic fracture.
• With poorly regulated Diabetes Mellitus type 1 and 2, neuropathies and generalized joint disease such as Rheumatoid Arthritis.
• That are assumed not compliant (drug use, cognitive- and/or psychiatric disorders).
• With previous history of ipsilateral ankle fracture.
• With previous history of ipsilateral major ankle-/foot surgery.