Measurement of finger joint motion after flexor tendon repair: smartphone photography compared with traditional goniometry

The purpose of our study was to determine whether smartphone photography is as reliable and valid as clinical goniometry for measuring interphalangeal joint range of motion. We conducted a retrospective review of 37 fingers in 33 patients after flexor tendon repair. The measurements on photographs taken with a smartphone by a surgeon were compared with manual measurements with goniometry by the same surgeon. Pearson coefficients and interclass correlation coefficients were all above 0.85, and Bland–Altman analysis demonstrated that at least 35 of 37 measurements were within the 95% confidence interval in all variables. According to the Tang criteria, the total number of excellent and good results were equivalent according to both methods. There was high interobserver reliability between measurements by surgeons and a therapist. We conclude that if the pictures are properly taken, the measurement of the angles in the smartphone pictures are as reliable as measuring the angles with goniometry and that grading of the results according to the two methods gives identical results.