Which Is the Best Outcome Measure for Rotator Cuff Tears?
Authors: Dabija Dominique I. , Pennings Jacquelyn S. , Archer Kristin R. , Ayers Gregory D. , Higgins Laurence D. , Kuhn John E. , Baumgarten Keith M. , Matzkin Elizabeth , Jain Nitin B. 
Published: July 2019

Abstract

Background
The American Shoulder and Elbow Surgeons Standardized Shoulder Form (ASES), the Shoulder Pain and Disability Index (SPADI), and the shortened Disability of the Arm, Shoulder, and Hand (quickDASH) are patient-reported upper extremity-specific outcome scales currently used to evaluate patients with rotator cuff tears. This heterogeneity does not allow for a uniform metric for research and patient care.

Questions/purposes
Our objective was to determine psychometric properties (reliability, convergent and discriminant validity, and responsiveness) of five commonly used outcome instruments (the ASES, the SPADI, the quickDASH, the SF-12, and the EuroQol-5D) in a longitudinal study of patients undergoing treatment for rotator cuff tears.

Methods
From February 2011 through June 2015, 120 patients completed a standardized history, the five outcome scales under study, a physical examination, and an MRI. Of these, 47 (39%) were lost to followup before 18 months, and another 24 (20%) were accounted for at 18 months but had missing data at one or more of the earlier prespecified followup intervals (3, 6, or 12 months). Reliability (the reproducibility of an outcome instrument between subjects; tested by Cronbach’s alpha), convergent and discriminant validity (determining which outcome measures correlate most strongly with others; tested by Spearman’s correlation coefficients), and responsiveness (the change in outcome scales over time based on percent improvement in shoulder functionality using the minimal clinically important difference [MCID] and the subjective shoulder value) were calculated.

Results
All outcomes measures had a Cronbach’s alpha above 0.70 (range, 0.74–0.94) and therefore were considered reliable. Convergent validity was demonstrated as the upper extremity-specific measures (SPADI, ASES, and quickDASH) were more strongly correlated with each other (rho = 0.74–0.81; p < 0.001) than with any of the other measures. Discriminant validity was demonstrated because the Spearman’s correlation coefficients were stronger for the relationships between upper extremity measures compared with the correlations between upper extremity measures and general health measures for 53 of the 54 correlations that were compared. Both internal and external responsiveness of the measures was supported. Patients who achieved the MCID and at least a 30% change on the subjective shoulder value had more positive change in scores over time compared with those who did not. Mixed model linear regressions revealed that all three upper extremity-specific measures had a group by time interaction for the MCID, indicating that patients who achieved the MCID had greater change over time compared with those who did not achieve the MCID. Results showed that the measure with the best discrimination between groups, or best internal responsiveness, was the ASES (beta = -8.26, 95% confidence interval [CI], -11.39 to -5.14; p < 0.001; η2 = 0.089) followed by the SPADI (beta = 6.88, 95% CI, 3.78–9.97; p < 0.001; η2 = 0.088) then the quickDASH (beta = 3.43, 95% CI, 0.86–6.01; p = 0.009, η2 = 0.027). Measures with the best external responsiveness followed the same pattern of results.

Conclusions
All the upper extremity-specific scales had acceptable psychometric properties. Correlations were high and thus only one upper extremity-specific instrument is needed for outcome assessment. Given the overall psychometric assessment, we recommend SPADI be the shoulder-specific instrument used to assess outcomes in patients with rotator cuff tears.

Level of Evidence
Level III, diagnostic study.