Comparison of multiple 3D scanners to capture foot, ankle, and lower leg morphology

Background: 3D scanning of the foot and ankle is gaining popularity as an alternative method to traditional plaster casting to fabricate ankle-foot orthoses (AFOs). However, comparisons between different types of 3D scanners are limited. Objective(s): The aim of this study was to evaluate the accuracy and speed of seven 3D scanners to capture foot, ankle, and lower leg morphology to fabricate AFOs. Study Design: Repeated-measures design. Methods: The lower leg region of 10 healthy participants (mean age 27.8 years, standard deviation [SD] 9.3) was assessed with 7 different 3D scanners: Artec Eva (Eva), Structure Sensor (SS I), Structure Sensor Mark II (SS II), Sense 3D Scanner (Sense), Vorum Spectra (Spectra), Trnio 3D Scanner App on iPhone 11 (Trnio 11), and Trnio 3D Scanner App on iPhone 12 (Trnio 12). The reliability of the measurement protocol was confirmed initially. The accuracy was calculated by comparing the digital scan with clinical measures. A percentage difference of #5% was considered acceptable. Bland and Altman plots were used to show the mean bias and limit of agreement (LoA) for each 3D scanner. Speed was the time needed for 1 complete scan. Results: The mean accuracy ranged from 6.4% (SD 10.0) to 230.8% (SD 8.4), with the SS I (21.1%, SD 6.8), SS II (21.7%, SD 7.5), and Eva (2.5%, SD 4.5) within an acceptable range. Similarly, Bland and Altman plots for Eva, SS I, and SS II showed the smallest mean bias and LoA 21.7 mm (LoA 25.8 to 9.3), 21.0 mm (LoA 210.3 to 8.3), and 0.7 mm (LoA 213 to 11.5), respectively. The mean speed of the 3D scanners ranged from 20.8 seconds (SD 8.1, SS I) to 329.6 seconds (SD 200.2, Spectra). Conclusions: Eva, SS I, and SS II appear to be the most accurate and fastest 3D scanners for capturing foot, ankle, and lower leg morphology, which could be used for AFO fabrication.