Concurrent validity of inclinometer measures of scapular and clavicular positions in arm elevation

Objective: To assess concurrent validity, between and within-day reliability of scapular and clavicular digital inclinometer measures. Design: Test-retest and concurrent validity. Setting: Laboratory. Participants: Twenty-three participants with and without shoulder symptoms. Main Outcome Measures: Static positions of scapular upward rotation, anterior/posterior tilting and clavicular elevation were measured between days with an inclinometer and compared to a 3-dimensional electromagnetic tracking system in different positions of sagittal plane humeral elevation (neutral, 30 degrees, 60 degrees, 90 degrees, 120 degrees). The two methods were compared using a two-way Analysis of Variance. Linear regressions at each arm position were also performed to further assess concurrent validity. Results: Between-day reliability demonstrated Intraclass Correlation Coefficients 0.50 for all comparisons. There were statistically significant differences between methods or interactions of method and arm position for clavicle elevation (p=0.004, maximum offset between methods 7.7o in the neutral position), and scapular upward rotation (p=0.001). For scapular upward rotation, the maximum difference between methods was less than 2 degrees across all humeral positions. Clavicle elevation (r=0.67-0.82) and scapular upward rotation (r=0.57-0.81) demonstrated higher correlations between measurement methods than scapular anterior/posterior tilt (r=0.10-0.67). Conclusions: Concurrent validity in assessing scapular upward rotation and clavicle elevation with an inclinometer was shown when compared with electromagnetic tracking. However, the inclinometer method may not have adequate concurrent validity to clinically measure scapular anterior/posterior tilting.