Responsiveness of the Shoulder Pain and Disability Index in patients with adhesive capsulitis

Background: Instruments designed to measure the subjective impact of painful shoulder conditions have become essential in shoulder research. The Shoulder Pain and Disability Index (SPADI) is one of the most extensively used scales of this type. The objective of this study was to investigate reproducibility and responsiveness of the SPADI in patients with adhesive capsulitis. Methods: SPADI test-retest reproducibility was estimated by the intraclass correlation coefficient (ICC) and the smallest detectable difference (SDD). Responsiveness was assessed by exploring baseline and follow-up data recorded in a recently reported clinical trial regarding hydrodilatation and corticosteroid injections in 76 patients with adhesive capsulitis. Standardized response mean (SRM) and reliable change proportion (RCP) for SPADI were compared with corresponding figures for shoulder range-of-motion (ROM). The relationship between SPADI and ROM change scores was investigated through correlation and linear regression analyses. Results: Results for test-retest reproducibility indicated a smallest detectable difference of 17 points on the 0-100 scale, and an intraclass correlation coefficient of 0.89. The SPADI was generally more responsive than ROM. Weak to moderately strong associations were identified between SPADI and ROM change scores. According to the regression model, the three variables baseline SPADI, baseline active ROM and change in active ROM together explained 60% of the variance in SPADI improvement. Conclusion: This study supports the use of SPADI as an outcome measure in similar settings.