Validity and reliability of a novel iPhone method to rapidly measure cervical sagittal parameters

We introduced a novel method based on the iPhone's intrinsic photo edit function to measure sagittal parameters of the cervical spine. This study aimed to assess the validity of this new method compared with the picture archiving and communication system (PACS) method (the gold standard) and to test the reliability of this novel technique. One hundred consecutive patients admitted to our hospital diagnosed with cervical spondylotic myelopathy or cervical spondylotic radiculopathy were retrospectively reviewed. Four angles, including the C0-2 Cobb angle, C2-7 Cobb angle, T1S and neck tilt (NT), were assessed by iPhone and PACS. The validity and reliability were evaluated, and the time taken by both methods was compared. The ICCs of the validity of the C0-2 Cobb angle, C2-7 Cobb angle, T1S and NT were 0.960, 0.976, 0.980 and 0.946, respectively. The ICCs of the intraobserver reliability of the C0-2 Cobb angle, C2-7 Cobb angle, T1S and NT were 0.966, 0.983, 0.971 and 0.951, respectively. The ICCs of the interobserver reliability of the C0-2 Cobb angle, C2-7 Cobb angle, T1S and NT were 0.953, 0.972, 0.957 and 0.929, respectively. The Bland‒Altman plot of validity of the four angles revealed mean differences of 0.3, 0.2, 0.1, and 0.1 degrees with 95% CIs of 4.1, 4.1, 2.9, and 4.3 degrees, respectively. The iPhone measurement time (58.55 ± 4.17 s) was significantly less than that by the PACS (70.40 ± 2.92 s) when compared by the independent-samples T test (P < 0.001). This novel method using the iPhone's intrinsic photo edit function is accurate, reliable, fast and convenient when measuring cervical sagittal parameters.