*2.1. Patients*

Fifteen patients who sustained a TAF (AO/OTA type B3) and underwent open reduction and internal fixation were retrospectively recruited. All patients underwent surgery between 2015 and 2018 at the Trauma Surgery department of the University Hospitals Leuven. Five patients had a luxation of the tibiotalar joint and two patients had a subluxation of the tibiotalar joint. None of the patient group had an open fracture. Polytrauma was not included in our study population. In total, 10 of the 15 patients obtained a temporary external fixator awaiting definitive internal fixation. The posterior malleolus and distal fibula fracture were addressed using plate screw osteosynthesis via a posterolateral approach, whereas the medial malleolus fracture was fixated using screws via a medial approach. Standardly one-third tubular plates with the small fragment system screws by DePuy Synthes™ (Raynham, MA, USA) were used to achieve anatomical reduction and internal fixation. If deemed necessary by the treating surgeon, variable angle LCP® was utilized in some cases. Additional syndesmotic screw fixation was performed if syndesmotic instability persisted after osseous fixation. Postoperatively, a fixed protocol was followed, consisting of immediate passive and active mobilization and toe-touch weight bearing (<10 kg) for 6 weeks. The control group consisted of 13 healthy subjects that were chosen at random from an existing database set-up in the same laboratory [6]. We matched a TAF subject to a control patient of the same gender, similar age, and walking speed to avoid the influence of confounding factors. An a priori sample size calculation showed that at least 12 patients and 12 control subjects were required to assure a minimal study power of 80% (β > 0.80). This calculation was based on biomechanical parameters reported in other

studies, including patients with ankle osteoarthritis or ankle fractures [13,15]. Informed consent was obtained from all participants and the ethical committee of the University Hospitals Leuven (S62064) approved the study.
