*2.3. Data Processing and Analysis*

The 3D inter-segment joint angles and joint coupling were calculated for the stance phase (0–62%) of the gait cycle. The swing phase of gait (63–100%) was not considered. In-house-made software (ACEPManager, Matlab 2016a, The Mathworks Inc., Natick, MA, USA) was used to normalize the time of the kinematic data to a 100% stance phase during the gait events. Kinematic variables of interest were subsequently calculated. We distinguished 4 sub-phases of the stance phase, i.e., the "loading response" (0–12%), "mid stance" (13–30%), "terminal stance" (31–50%), and "pre-swing" (51–62%) phases. Kinematic variables of interest were subsequently determined by calculating the ROM in each subphase. The latter was carried out by calculating the difference between the maximum and minimum value in the respective sub-phase. Furthermore, the patient-reported outcome measures, using the ankle–hindfoot scale (AOFAS), the EuroQol health scale (EQ-5D), and the EQ-5D visual analogue scale (VAS), were evaluated. The AOFAS monitors the progression of patients after foot and ankle surgery, the EQ-5D records the health state as rated by the caregiver, and the EQ-5D VAS assumes the individual's health state valuation [17,18].
