Validation of the Brazilian Portuguese Version of the Western Ontario Shoulder Instability Index (WOSI) Questionnaire.

 To evaluate the validity of the Brazilian Portuguese version of the Western Ontario Shoulder Instability Index (WOSI).  We assessed 51 patients aged 18 to 40 years who were divided into 3 groups: 17 patients with shoulder instability undergoing conservative treatment, 17 with shoulder instability treated surgically, and 17 without shoulder instability. The patients underwent functional and health assessments using the following scores: WOSI, Rowe, Visual Analog Scale (VAS), Subjective Shoulder Value (SSV), Disabilities of the Arm, Shoulder and Hand (DASH), and University of California-Los Angeles (UCLA) Shoulder Scale.  The variables sex and age were homogeneous among the groups (  > 0.05). A comparative analysis of the scores revealed that patients undergoing treatment (either surgical or conservative) showed significant differences compared with the control group (  < 0.05). The determination of score correlation was made using the Spearman correlation coefficient. All instruments analyzed showed a significant relationship among themselves but at different levels: the correlation between the WOSI and DASH instruments was perfectly positive (  = 0.96); the comparison of the WOSI and UCLA (  = 0.87), DASH and UCLA (  = 0.86), SSV and Rowe (  = 0.80), VAS and DASH (r = 0.75), VAS and UCLA (  = 0.74), and WOSI and VAS (  = 0.72) also showed a trend towards positive linearity among measurements; and the comparison of the instruments WOSI and SSV, WOSI and Rowe, DASH and Rowe, SSV and UCLA (  = -0.83), SSV and DASH (  = -0.79), Rowe and UCLA (  = -0.78), VAS and SSV (  = -0.68), and VAS and Rowe (  = -0.60) revealed a negative correlation.  The Brazilian Portuguese version of the WOSI presents good validity.