The reliability and accuracy of an electromagnetic motion analysis system when used conjointly with an accelerometer

The effect of an accelerometer driven electronic postural monitor (Spineangel (R)) placed within the electromagnetic measurement field of the Polhemus Fastrak (TM) is unknown. This study assessed the reliability and accuracy of Fastrak (TM) linear and angular measurements, when the Spineangel (R) was placed close to the sensor(s) and transmitter. Bland Altman plots and intraclass correlation coefficient (2,1) were used to determine protocol reproducibility and measurement consistency. Excellent reliability was found for linear and angular measurements (0.96, 95% CI: 0.90-0.99; and 1.00, 95% CI: 1.00-1.00, respectively) with the inclusion of Spineangel (R); similar results were found, without the inclusion of Spineangel (R), for linear and angular measurements, (0.96, 95% CI: 0.89-0.99; and 1.00, 95% CI: 1.00-1.00, respectively). The greatest linear discrepancies between the two test conditions were found to be less than 3.5 mm, while the greatest angular discrepancies were below 3.5 degrees. As the effect on accuracy was minimal, these findings support the conjoint use of the Fastrak (TM) during validation studies of the Spineangel (R) device.