Background: Having an estimate of the measurement error of self-report questionnaires is important both for assessing follow-up results after treatment and when planning intervention studies. Specific questionnaires have been evaluated for patients with shoulder instability, but not in particular for patients with SLAP (superior labral anterior posterior) lesions or recurrent dislocations. The aim of this study was to evaluate the agreement, reliability, and validity of two commonly questionnaires developed for patients with shoulder instability and a generic questionnaire in patients with SLAP lesions or recurrent anterior shoulder dislocations.
Methods: Seventy-one patients were included, 33 had recurrent anterior dislocations and 38 had a SLAP lesion. The patients filled in the questionnaires twice at the same time of the day (± 2 hours) with a one week interval between administrations. We tested the Oxford Instability Shoulder Score (OISS) (range 12 to 60), the Western Ontario Shoulder Instability Index (WOSI) (0 to 2100), and the EuroQol: EQ-5D (-0.5 to 1.0) and EQ-VAS (0 to 100). Hypotheses were defined to test validity.
Results: ICC ranged from 0.89 (95% CI 0.83 to 0.93) to 0.92 (0.87 to 0.95) for OISS, WOSI, and EQ-VAS and was 0.66 (0.50 to 0.77) for EQ-5D. The limits of agreement for the scores were: -7.8 to 8.4 for OISS; -339.9 to 344.8 for WOSI; -0.4 to 0.4 for EQ-5D; and -17.2 and 16.2 for EQ-VAS. All questionnaires reflect the construct that was measured. The correlation between WOSI and OISS was 0.73 and ranged from 0.49 to 0.54 between the shoulder questionnaires and the generic questionnaires. The divergent validity was acceptable, convergent validity failed, and known group validity was acceptable only for OISS.
Conclusion: Measurement errors and limitations in validity should be considered when change scores of OISS and WOSI are interpreted in patients with SLAP lesions or recurrent shoulder dislocations. EQ-5D is not recommended as a single outcome.