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°, 60°, 90°, 120°). 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 7.7° in the neutral position), and scapular upward rotation (p = 0.001). For scapular upward rotation, the maximum difference between methods was less than 2° 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 electro-magnetic tracking. However, the inclinometer method may not have adequate concurrent validity to clinically measure scapular anterior/posterior tilting.