Supplementary Material for: Validity and Reliability of Two Digital Wound Measurement Tools after Surgery in Patients with Hidradenitis Suppurativa

<b><i>Background:</i></b> After excision surgery in patients with hidradenitis suppurativa (HS), wounds are usually left open for secondary intention healing. To evaluate wound healing, reliable wound measurement is important. However, digital wound measurement tools for measuring the surface area are validated for small wounds located on flat or mildly convex body surfaces in studies, often powered inadequately. Up until now, a validated digital measurement tool to accurately measure wounds on all body surfaces, including the intertriginous areas, was not available. <b><i>Objectives:</i></b> The aim of this study was to validate two digital wound measurement tools for the measurement of the surface area of larger and concave wounds, using surgical wounds in patients with HS. <b><i>Methods:</i></b> This prospective observational validation study included consecutive patients with HS undergoing excision surgery in the Department of Dermatology of the Erasmus University Medical Center, Rotterdam. Wound measurements using a ruler, the tracing method, the inSight® 3-dimensional (3D) device, and the ImitoWound app were performed by three investigators. The intraclass correlation coefficients (ICCs) for concurrent validity and the intra- and inter-rater reliability were analyzed. The standard error of measurement (SEm) and minimal detectable change were calculated, and Bland-Altman plots were constructed to determine the limits of agreement. <b><i>Results:</i></b> Twenty patients with a total of 52 wounds were included. The wounds had a mean surface of 18.7 cm². The inSight® 3D device showed an ICC of 0.987 for concurrent validity, 0.998 for intra-rater reliability, and 0.997 for inter-rater reliability. The ICCs from the ImitoWound application were 0.974, 0.978, and 0.964 for concurrent validity, intra-rater reliability, and inter-rater reliability, respectively. The SEms for intra- and inter-rater reliability were 0.95 cm² and 1.11 cm² for the inSight® 3D device and 3.33 cm² and 3.51 cm² for the ImitoWound app, respectively. <b><i>Conclusion:</i></b> Both the inSight® 3D device and the ImitoWound app demonstrated excellent concurrent validity and reliability for the surface measurements of concave wound, enabling these tools to be used reliably in clinical research and daily practice. Furthermore, it paves the way for broader application, such as telemonitoring of wound care at home.