Patients treated in our level-1 trauma center for dislocated ankle fractures between January 2011 and April 2023 were retrospectively identified using the clinical electronic information system.

Inclusion criteria were the presence of an ankle fracture dislocation and age ≥ 18 years. Exclusion criteria were an open fracture, incomplete radiological documentation, definitive osteosynthesis within 24 h after trauma, history of fracture or surgery of the same ankle, a pathological fracture, refused informed consent to participate in a study or the immediate application of an external fixator. The indication to perform an immediate ankle spanning external fixator application was at the discretion of the attending surgeon.

The primary outcome was the rate of insufficient reduction during initial immobilization in the cast. Secondary outcomes included time to definitive surgery, length of surgery and hospital length of stay.

All electronic records of the eligible patients were reviewed and the following data was abstracted and analyzed: demographics (age, gender, Body Mass Index (BMI)), comorbidities (diabetes mellitus, smoking, alcohol abuse, osteoporosis, vascular disease), fracture classification according to the AO/OTA [8,7,8], medial clearspace, presence and size of a posterior malleolar fragment (PMF), initial percentage of tibiotalar dislocation, treatment history (primary external fixation, primary cast immobilization, quality of reduction, time to surgery, duration of surgery and time to discharge).

An ankle fracture dislocation was defined as a loss of congruity of the ankle joint space, depicted by an enlargement of the medial clear space > 5 mm in the anterior posterior (ap) x-ray of the ankle and/or anteroposterior dislocation (subluxation) of the talus relative to the tibia of > 5 mm in the lateral x-ray of the ankle that was initially performed (Fig. 1) [22]. The medial clearspace was measured as the widest distance between the medial border of the talus and the lateral border of the medial malleolus [23]. If these criteria were met, immediate closed reduction of the ankle joint was performed under sedation, if possible due to pain, or under short anesthesia by the emergency doctor on call. The congruence of the ankle joint was therefore restored under xray control and a split plaster cast was applied.

The initial dislocation in percentage was measured using the x-ray. For this purpose the axis of the tibia and the talus were defined in the a anterior posterior radiograph and the dislocation of this two lines was measured [24]. In addition, the calculated dislocation was set in relation to the width of the talus at the level of the joint surface.

Insufficient reduction in the cast was defined by an incongruent tibiotalar joint with a widening of the medial clearspace > 5 mm on the anterior posterior view and/or an anterior-posterior dislocation of > 5 mm on the lateral view in the x-ray or the CT scan that was immediately performed after the initial reduction and casting [25].

The sagittal diameter of the PMF was measured in the CT scan. The longest extension in the sagittal plane was used for this purpose [26].

In contrast, the percentage of the PMF in the tibial joint surface was calculated using the lateral radiograph according to Fig. 2 [27].

The common classification according to Haraguchi was also used to classify posterior malleolar fractures, which divides the fractures into 3 types depending on extension and localization [28].

Anterior posterior radiograph of a trimalleolar ankle fracture. The left image shows the ankle in its prereduction state. The black arrow shows the medial clearspace expanded to 8.3 mm. The right image shows the ankle post reduction in computed tomography. The white diamond shows the measured medial clearspace of 4.2 mm

Lateral radiograph of a trimalleolar ankle fracture. The ratio between the width of the PMF and the width of the tibia defines the percentage of the PMF in the tibial joint surface, as well as the sagittal diameter

In our clinic, as standard of care, immediate closed fracture reduction under fluoroscopy is performed in the emergency department. Subsequently, a below-the-knee open circular cast is applied to retain the reduction. Following reduction and casting, computed tomography of the upper ankle joint is performed for exact fracture evaluation and preoperative planning.

After a decrease of the swelling, definitive open reduction and internal fixation is performed. Following surgery, the ankle is immobilized in a plantigrade position in a cast, with no weight bearing initially and partial weight bearing with crutches over time, for a total of 6–12 weeks depending on the fracture severity and soft tissue injuries. Low-molecular-weight heparin is routinely administered for thromboembolism prophylaxis. Routine follow-ups for clinical and radiologic evaluation are set at 3, 6, 12, 24, and 52 weeks.

The patients were stratified into two groups: sufficient versus insufficient closed reduction. The p values for categorical variables were derived from the Pearson’s Chi-sqare or the 2-sided Fisher’s exact test. For continuous variables the Student’s t-test or the Mann-Whitney tests were deployed.

To identify risk factors independently associated with an insufficient reduction, a stepwise logistic regression model was utilized and risk factors from the bivariate analysis with a p value < 0.2 were included into the model.

Receiver operating characteristic (ROC) curves were constructed to analyze different variable’s discriminating power for predicting insufficient reduction, and the areas under the ROC curve were compared.

Values are reported as mean ± standard deviation (SD) for continuous variables and as percentages for categorical variables.

Differences were considered statistically significant when p ≤ 0.05. The data were analyzed using the Statistical Package for Social Sciences (SPSS Windows©), version 26 (SPSS Inc., Chicago, IL).

for this study was received by the local ethical committee (2021 − 00646).