Validity and internal consistency of the Helsinki Serratus Palsy Index for patients with serratus palsy.

Background: To our knowledge, no validated scales exist as yet for measuring quality of life and functioning level in patients with serratus palsy. This cross-sectional survey study examined whether a broadly validated Western Ontario Rotator Cuff Index (WORC) could be partially adapted for patients with serratus palsy.

Methods: The relevancy of WORC, 21 items, along with 4 additional new items, was tested by 95 patients with serratus palsy and a panel of 9 medical experts. Its content validity was measured by a content validity index (CVI), a content validity ratio (CVR), and a modified κ. The internal consistency of 11 retained items was assessed with the Cronbach α. Its construct validity was assessed by exploratory factor analysis.

Results: Of the 25 items, 11 were considered relevant (CVI ≥0.78) for serratus palsy by the panelists, with overall test CVI (S-CVI) of 0.86. The internal consistency of these 11 items was excellent, with a Cronbach α of 0.94. The exploratory factor analysis accompanied by a parallel analysis confirmed the unidimensionality of a new test. All except 2 items of WORC that were considered relevant by the panelists were also marked with scores of >5 by the patients on an 11-point scale of relevancy.

Conclusions: Adapted from the WORC, the new 11-item Helsinki Serratus Palsy Index scale was internally consistent and face and content valid for serratus palsy patients.