Validity of the digital inclinometer and iphone when measuring thoracic spine rotation

Abstract

Context: Spinal axial rotation is required for many functional and sporting activities. Eighty percent of axial rotation occurs in the thoracic spine. Existing measures of thoracic spine rotation commonly involve laboratory equipment, use a seated position, and include lumbar motion. A simple performance-based outcome measure would allow clinicians to evaluate isolated thoracic spine rotation. Currently, no valid measure exists. Objective: To explore the criterion and concurrent validity of a digital inclinometer (DI) and iPhone Clinometer app (iPhone) for measuring thoracic spine rotation using the heel-sit position. Design: Controlled laboratory study. Setting: University laboratory. Patients or Other Participants: A total of 23 asymptomatic healthy participants (14 men, 9 women; age=25.82 6 4.28 years, height = 170.26 6 8.01 cm, mass = 67.50 6 9.46 kg, body mass index = 23.26 6 2.79) were recruited from a student population. Main Outcome Measure(s): We took DI and iPhone measurements of thoracic spine rotation in the heel-sit position concurrently with dual-motion analysis (laboratory measure) and ultrasound imaging of the underlying bony tissue motion (reference standard). To determine the criterion and concurrent validity, we used the Pearson product moment correlation coefficient (r, 2 tailed) and Bland-Altman plots. Results: The DI (r=0.88, P > .001) and iPhone (r=0.88, P > .001) demonstrated strong criterion validity. Both also had strong concurrent validity (r = 0.98, P >.001). Bland-Altman plots illustrated mean differences of 5.828 (95% confidence interval [CI] = 20.378, °8.738) and 4.948 (95% CI = 19.238, °9.358) between the DI and iPhone, respectively, and the reference standard and 0.878 (95% CI = 6.798, °5.058) between the DI and iPhone. Conclusions: The DI and iPhone provided valid measures of thoracic spine rotation in the heel-sit position. Both can be used in clinical practice to assess thoracic spine rotation, which may be valuable when evaluating thoracic dysfunction.