Psychometric properties of 3 patient-reported outcome measures for the assessment of shoulder disability after neck dissection

Background: Patient-reported outcome measures evaluating shoulder disability after neck dissection (ND) have not been sufficiently validated. We assessed the psychometric properties of the Shoulder Disability Questionnaire (SDQ), Neck Dissection Impairment Index (NDII) and the Shoulder Pain and Disability Index (SPADI) in patients after ND.

Methods: 107 patients completed the SDQ, NDII and SPADI on 4 occasions over 6 months, and underwent physical examination. We assessed internal consistency, test-retest reliability, clinical- and construct validity, and responsiveness to change. The possibility of combining the NDII and SPADI items into a single scale was explored by Rasch-analysis.

Results: All questionnaires exhibited good reliability and validity. We were successful in fitting a Rasch model to the data.

Conclusion: The results support the suitability of the SDQ, NDII and the SPADI for use in ND patients. Combining the SPADI and NDII in a single Rasch-scale improves item difficulty distribution, but reduces variability and discriminative ability.