Reliability and minimal detectable change of 3-dimensional scapular orientation in individuals with and without shoulder impingement.

STUDY DESIGN: Clinical measurement.

OBJECTIVE: To establish trial-to-trial within-day and between-day reliability, standard error of measurement, and minimal detectable change of scapular orientation during elevation and lowering of the arm, and with the arm relaxed at the side, in individuals with and without shoulder impingement.

BACKGROUND: Electromagnetic devices are commonly used to measure 3-D scapular kinematics during arm elevation in different conditions and for intervention studies. However, there is a lack of studies that evaluate within- and between-day reliability of these measurements.

METHODS: The subjects were allocated to either a control group or an impingement group. Kinematic data were collected using the Flock of Birds electromagnetic device during elevation and lowering of the arm in the sagittal plane on 2 different occasions, separated by 3 to 5 days. Forty-nine subjects were tested for within-day reliability. Forty-three subjects were reassessed for between-day reliability.

RESULTS: Intraclass correlation coefficients for within- and between-day assessment of scapular orientation during elevation and lowering of the arm in both groups ranged from 0.92 to 0.99 and from 0.54 to 0.88, respectively. Intraclass correlation coefficients for assessment of scapular orientation with the arms relaxed at the side in both groups ranged from 0.66 to 0.95. The standard error of measurement for between-day measurements ranged from 3.37° to 7.44° for both groups. The minimal detectable change for between-day measurements increased from 7.81° at the lower to 17.27° at the higher humerothoracic elevation angles.

CONCLUSION: These results support the use of Flock of Birds to measure scapular orientations in subjects with and without impingement symptoms. The measurements showed excellent within-day reliability but were not highly reliable over time.