# Evaluation of Patients with Hallux Valgus Wearing a 3D-Printed Orthosis during Walking
## 2 Material and Methods  
This study included 12 patients (9 female; 3 male; mean age: 26.7 \(\pm\) 9.8 years old). The inclusion criteria were following: (1) the participant was older than 20 years old; (2) the HV angle was greater than 20 degrees; (3) the participant did not previously receive any forms of foot surgery. The HV angle of the participants in the study was 26.5 \(\pm\) 4.9\({}^{\circ}\). The exclusion criteria included prior lower limb surgery, active inflammation, foot deformity, and any lesser toe deformity. Since a previous study [10] reported that the HV angle of a normal foot was within 10 degrees, the normal foot model with a HV angle of 10 degrees was used to create an orthosis model. The primary contours of the great toe and first metatarasus were edited using 3D modelling software Meshmixer (Autodesk Inc., San Francisco, CA, USA) (Figure 1A). In consideration of the gap between the foot and shoe, the thickness of the 3D-printed orthosis was set at 2.5 mm. The size of the orthosis was according to the participant's foot length to scale it. The digital data were exported in stereolithography file format, as required for subsequent 3D printing. The 3D printer Finder (FlashForge Corporation, Hangzhou, Zhejiang, China) was used to fabricate the orthosis with Flash Print slicing software (FlashForge Corporation, Hangzhou, Zhejiang, China) (Figure 1B). Thermoplastic polyurethane was used as the printing material, and the printing parameters were set as 0.18 mm thickness per layer, 100% filling density, 210 \({}^{\circ}\)C printing temperature, and 30 mm/s printing speed. Figure 1: _Cont._  
The orthosis was applied to maintain the great toe in a corrected position and allowed a prolonged stretch to the surrounding soft tissue, and a loop was created around the orthosis. Strap force was applied for the hallux to be adducted by the loop (Figure 1C). The bottom of the first metatarsal joint was kept hollow to provide adequate push-off phase of gait. To realise the kinematic effect of wearing a 3D-printed orthosis in terms of both static and dynamic motion, a Vicon motion capture system (Oxford Metrics, Oxford, UK) with eight cameras operating at 120 Hz was used along with 13 passive reflective markers placed on each foot for the kinematic analysis, as shown in Figure 2. The hallux movement was measured using the model according to a previously described procedure [11]. The participants walked at a self-selected speed along a 6-m walkway with force plates embedded in the floor. Three-dimensional motion data were captured from at least three walking trials. The relative motion occurring at the intersement angle was calculated for the following gait events of the stance phase: loading response (0-16%), mid-stance (16-50%), terminal stance (50-83%), and preswing (83-100%). The ground reaction force (GRF) was estimated to quantify the kinetic changes observed in the foot of patients wearing the orthosis. The GRF was recorded using a force plate for each walking trial. Throughout the stance phase, two components of the GRF vectors, in vertical and anterior-posterior directions, were analysed. The magnitude of the GRF component was normalised according to the body weight of each individual. The same participants were respectively tested without orthosis (Barefoot) and with orthosis (3 DP_orthosis). SPSS Statistics 20.0 (IBM Corporation, Armank, NY, USA) was used for statistical analysis. A paired sample \(t\) test was performed to compare the difference between the Barefoot and 3 DP_orthosis; the significance level was set as 0.05. To figure out the participant's feelings, the study also conducted a comfort score to inquire about the participant's response. The comfort score ranged from 0 to 10 points. The  
Figure 1: Manufacture of the 3D-printed orthosis: (**A**) Design of the 3D-printed orthosis model. The toe is divided into three parts. The toe part forms a loop shape. The arrows indicate strap and corrective forces. (**B**) 3D-printed orthosis. (**C**) Correction of hallux valgus.