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 disabilities. It is important to assess the responsiveness and interpretability of the SPADI when it is used by patients seeking help by a physical therapist for their shoulder pain in 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 consulting a physical therapist for their shoulder pain. Patients received physical therapy treatment and completed the Dutch language version of the SPADI (SPADI-D) at baseline and at follow up of 26 weeks. To assess the interpretability floor and ceiling effects and the minimal important change (MIC) using the ROC method including a visual anchor based MIC distribution for several Global Perceived Effect scale (GPE) based anchors was used. The measurement error was calculated using the Smallest Detectable Change (SDC). For the responsiveness, the Area under the ROC curve (AUC) 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 In total 356 patients participated at baseline and 237 (67%) returned the SPADI after 26 weeks. The mean score at baseline of the SPADI was 46.7 points (on a 0-100 scale). The SPADI showed no signs of floor and ceiling effects. The SDC was 19.7 points. The MIC was 20 (43% of baseline value) and therefore we consider a change of more than 43% or more in an individual patient as clinically relevant. The AUC was 0.81, the Spearman correlation between the SPADI change score and the GPE was 0.53 and the Pearson correlation between the SDQ and the SPADI change scores 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. J Orthop Sports Phys Ther, Epub 3 Feb 2017. doi:10.2519/jospt.2017.7079