A smartphone is an equivalent Cobb measurement tool to the manual protractor


Smartphones can be used for measuring Cobb angles in patients with spinal deformities, a study published by Matthew Shaw, Brisbane, Australia, and colleagues in the June issue of the European Spine Journal has found.

Matthew Shaw, Paediatric Spine Research Group, Queensland University of Technology and Mater Health Services, Brisbane, Australia, and colleagues reported that the “Cobb method” is still the most popular method of assessing spinal curves. Traditionally, the method involves spinal specialists using a protractor and a pencil on hardcopy radiographic films to measure Cobb angles. Although computer programmes for measuring Cobb angles are available, according to Shaw et al, they are not universally accessible and some can be too complex for routine use. Shaw et al stated smartphones often incorporate a micro-electro-mechanical-system (MEMS) accelerometer that can be used to detect acceleration and inclination. They wrote: “The availability of various software applications for smartphones, which read and display the accelerometer signal allow them to be used in a wide range of potential clinical applications.” The aim of their study, therefore, was to compare the performance of an iPhone App (Tiltmeter Pro software, IntegraSoft) with that of a standard protractor for the assessment of coronal Cobb angles.

Seven observers (including two spinal orthopaedic specialists) measured the major Cobb angle of 20 coronal plane radiographs, first using the smartphone App and then using a protractor. To assess inter- and intraobserver variations, five of the seven observers performed a second set of measurements a week after the first sets of measurements were taken.

Overall, there were 239 pairs of protractor/smartphone measurements taken. Shaw et al wrote: “The differences between iPhone and protractor measurements were small, with a mean absolute difference of just over 2 degrees, bias of 1 degree and a 95% confidence interval of just over 3 degrees. All of these are much less than the 5 degree difference which is widely accepted as signifying a clinical significant difference in Cobb angle.” They added that inter- and intraobserver measurement variability with the smartphone was similar to that of the protractor and within the range of studies on protractor measurements.

According to Shaw et al, after “appropriate comparison with manual techniques”, smartphones could “likely be used in a range of clinical measurement situations.” They explained that the basis of the Cobb measurement technique is the same as the techniques used for post-operative Cobb measurements or sagittal plane kyphosis/lordosis measurements. Therefore, as smartphones (in this study) appear to be clinically equivalent measurement tool to a protractor, they may be able to be used in other instances.

Study investigator Clayton Adam, associate professor, Queensland University of Technology and Mater Health Services, Brisbane, Australia, told Spinal News International: “The main implication of the study is that the increasing number of clinicians who own smartphones are already carrying around an inclination measurement tool that can be used to quickly and effectively track the progression of deformity in scoliosis and other spinal deformities.”