Structural validity and internal consistency of the Shoulder Pain and Disability Index in Turkish patients with rotator cuff disease: A proposal of a new version.

Background: The Shoulder Pain and Disability Index (SPADI) is a widely used patient-reported outcome questionnaire in patients with shoulder diseases; however, the structural validity and the internal consistency of the Turkish SPADI is unclear in rotator cuff disease.

Objective: To assess the internal structure of the Turkish SPADI in patients with rotator cuff disease.

Methods: A total of 109 patients with unilateral rotator cuff disease were assessed. The COnsensus-based Standards for the selection of health Measurement INstruments checklist was used for the methodological design of the study. A confirmatory factor analysis was performed, and the model fit was assessed by using the comparative fit index (CFI), the Tucker-Lewis index (TLI), the root mean square error of approximation (RMSEA), and the standardized root mean square residual (SRMR). The factor structure was examined with a principal component analysis. The internal consistency was assessed using Cronbach's alpha.

Results: The validity of the two subscales was not confirmed. The principal component analysis showed the Turkish SPADI consisted of one factor, and the one-factor model of the Turkish SPADI also was not confirmed. When two items were deleted, the one-factor model of the new version of the Turkish SPADI had a better fit (CFI = 0.978, TLI = 0.971, RMSEA = 0.058, SRMR = 0.043). The internal consistency of the new version of the Turkish SPADI was high (Cronbach's alpha = 0.92, 95% CI = 0.90-0.94).

Conclusions: We suggest that the modified version of the Turkish SPADI should be used for patients with rotator cuff disease. The total score of the modified version should be considered.