Reference Values of the Pain Disability Index in Patients With Painful Musculoskeletal and Spinal Disorders: A Cross-national Study.

Study Design: Cross-sectional study.

Objective: To examine reference data for the Pain Disability Index (PDI) in Dutch and Canadian patient samples with a variety of musculoskeletal pain disorders and to test which potential factors are independently associated with the PDI score.

Summary Of Background Data: The PDI is a widely used generic instrument for measuring disability related to pain. It is unknown whether patients with spinal and other musculoskeletal diagnoses have different levels of disability when scored on the PDI.

Methods: Patients were referred to secondary and tertiary care centers in the Netherlands and Alberta, Canada, between 2009 and 2013. All patients filled out a baseline questionnaire including demographics and the PDI. After first consultation with a medical doctor, diagnoses were set by the medical specialist. Univariate general linear models were used to examine correlations between PDI scores and age, sex, country of residence, diagnosis, and work status.

Results: In total 6997 patients were included in this study: 1302 Canadian and 5695 Dutch patients. Mean PDI score of the total group was 37.8 ± 14.2. Reference values are presented and clustered into the following diagnostic groups: spinal nerve and intervertebral disc disorders; nonspecific back pain; rheumatic soft-tissue pain (widespread pain or fibromyalgia); spinal stenosis; and whiplash-associated disorder. The PDI score was significantly and relevantly associated with pain intensity (η explained variance from 20% to 25%), but not relevantly associated with age, sex, country of residence, and diagnostic group (η<3%). In the working subgroup, adding "current sick leave" as covariate increased the explained variance to 34%.

Conclusion: Reference values of the PDI are presented. Patient ratings of disability on the PDI are relevantly associated with pain intensity and work status, but not with nationality or diagnostic group. Only minimal differences were identified between the various musculoskeletal diagnoses included.

Level Of Evidence: N/A.