Digital Image Processing Technique To Measure The Range Of Motion Of The Elbow

Background: Most photography-based arc of motion measurements require human assessment and their accuracy depends on the observer.Objectives: To develop a digital image processing technique (DIPT) for measuring elbow range of motion (ROM), and to assess its validity and reliability compared with standard methods.Methods: Physiotherapists performed digital goniometer and inclinometer ROM measurements bilaterally on healthy volunteer elbows. A photographer took digital images of elbows fully extended and fully flexed 3 times using an 8-megapixel smartphone camera. Extension and flexion angles were calculated using the DIPT. Intra- and inter-rater reliability of all methods was assessed using an intraclass correlation coefficient (ICC). A paired Student's t test and Wilcoxon-signed rank test were used to assess systematic bias. A Bland-Altman plot was used to show possible range of difference between the methods.Results: We measured 56 elbows from 28 participants. Intra- and inter-rater ICCs of goniometer and inclinometer showed moderate-to-excellent agreement. Mean extension and flexion angles for the DIPT were greater than those for the goniometer and inclinometer measurements (P < 0.05), but the total ROMs were not significantly different (vs goniometer P = 0.32, vs inclinometer P = 0.53). Limits of agreement were 9.93 degrees-10.05 degrees for extension angle, 9.81 degrees-11.7 degrees for flexion angle, and 13.84 degrees-15.99 degrees for total ROMs.Conclusions: Elbow ROM measurement using the current DIPT produces results comparable with goniometer and inclinometer measurements, but the difference from the standard methods was up to 15.99 degrees for total ROM.