Test–Retest Reliability and Convergent Validity of Two Scoring Versions of the Spinal Appearance Questionnaire Against Radiographic Measurements and Established Quality of Life Questionnaires in Adolescents with Idiopathic Scoliosis

<b>Background/Objectives</b>: The Spinal Appearance Questionnaire (SAQ) assesses the self-perception of appearance of adolescents with idiopathic scoliosis (AIS). Due to originally scoring too many domains and producing prevalent ceiling effects when treated conservatively, the SAQv1.1, has been introduced. This study aimed to compare the test-retest reliability, convergent validity, and ceiling and floor effects of the two versions of the SAQ in patients with AIS. <b>Methods</b>: Conservatively treated females with AIS, aged 10-18 years old, were consecutively recruited from a scoliosis clinic. The Scoliosis Research Society-22 refined (SRS-22r), SAQ, and SAQv1.1 were collected, in English, with radiographic measurements (Cobb angle, Coronal Balance, and Vertebral Rotations). Nine domain scores were obtained from the original SAQ. Appearance, Expectations, and Total scores were calculated for SAQ v.1.1. Questionnaires were re-administered electronically after one week. <b>Results</b>: One hundred females, aged 13.9 ± 1.8 years with curve angles of 28.8° ± 13.9°, were included. The test-retest reliability for SAQ varied between domains (ICC_3,1 = 0.72 to 0.94). The Total, Appearance, and Expectation ICCs_3,1 for the SAQv1.1 were 0.92, 0.94, and 0.86, respectively. Convergent validity was demonstrated between seven SAQ domains and the SRS-22r Total and Cobb angle (|r| = 0.32 to 0.59). The SAQv1.1 Total correlated with the SRS-22r Total (r = -0.50) and with the Cobb angle (r = 0.56). All SAQ domains presented ceiling (Curve = 11% to Kyphosis = 68%) and floor effects (Chest = 8% and Waist = 4%). The SAQv1.1 Total and Appearance had low ceiling effects (≤5%), while Expectations presented both ceiling (14%) and floor effects (10%). <b>Conclusions</b>: The SAQv1.1 is recommended because of its stronger reliability, superior convergent validity, and fewer ceiling and floor effects in AIS.