The responsiveness and interpretability of the shoulder pain and disability index

STUDY DESIGN: Clinical measurement study, prospective cohort design. BACKGROUND: Shoulder pain is a common disorder, and treatment is most often focused on a reduction of pain and functional disabilities. Several reviews have encouraged the use of the Shoulder Pain and Disability Index (SPADI) to objectify functional disability. It is important to assess the responsiveness and interpretability of the SPADI in patients seeking physical therapy treatment for their shoulder pain in a primary care setting. OBJECTIVE: To assess the responsiveness and interpretability of the SPADI in patients with shoulder pain visiting a physical therapist in primary care. METHODS: The target population consisted of patients who consulted a physical therapist for their shoulder pain. The patients received physical therapy treatment and completed the Dutchlanguage version of the SPADI at baseline and at 26-week follow-up. The interpretability floor and ceiling effects and the minimal important change (MIC) were assessed using the receiver operating characteristic method, and a visual anchor-based MIC distribution method was used to assess several Global Perceived Effect scale (GPE)-based anchors. The measurement error was calculated using the smallest detectable change. For the responsiveness, the area under the receiver operating characteristic curve was used, and correlations with the GPE and the change score of the Shoulder Disability Questionnaire (as this questionnaire measures the same construct) were assessed. RESULTS: A total of 356 patients participated at baseline and 237 (67%) returned the SPADI after 26 weeks. The mean score on the SPADI at baseline was 46.7 points (on a 0-100 scale). The SPADI showed no signs of floor and ceiling effects. The smallest detectable change was 19.7 points. The MIC was 20 (43% of baseline value), and therefore a change of 43% or more in an individual patient was considered to be clinically relevant. The area under the receiver operating characteristic curve (AUC) was 0.81, the Spearman correlation between the SPADI change score and the GPE was 0.53, and the Pearson correlation between the Shoulder Disability Questionnaire and the SPADI change score was 0.71. CONCLUSION: The results of this study confirm the responsiveness of the SPADI, making it a useful instrument to assess functional disability in longitudinal studies; however, the measurement error should be taken into account when making decisions in individual patients.