Test-retest reliability of posture measurements in adolescents with idiopathic scoliosis

Posture changes are a major consequence of idiopathic scoliosis (IS). Posture changes can lead to psychosocial and physical impairments in adolescents with IS. Therefore, it is important to assess posture, but the test-retest reliability of posture measurements still remains unknown in this population. The primary objective of the present study was to determine the test-retest reliability of 25 head and trunk posture indices using the Clinical Photographic Postural Assessment Tool (CPPAT) in adolescents with IS. The secondary objective was to determine the standard error of measurement and the minimal detectable change. This is a prospective test-retest reliability study carried out at two tertiary university hospital centers. Forty-one adolescents with IS, aged 10–16 years old with curves 10°–45° and treated by medical intervention, were recruited. Two posture assessments were done using the CPPAT 5–10 days apart following a standardized procedure. Photographs were analyzed with the CPPAT software by digitizing reference landmarks placed on the participant by a physiotherapist evaluator. Generalizability theory was used to obtain a coefficient of dependability, standard error of measurement, and the minimal detectable change at 90% confidence interval. Fourteen of 25 posture indices had a good reliability (ϕ≥0.78), 10 had moderate reliability (ϕ=0.55–0.74), and 1 had poor reliability (ϕ=0.45). The most reliable posture indices were waist angle asymmetry (ϕ=0.93), right waist angle (ϕ=0.91), and frontal trunk list (ϕ=0.92). Right sagittal trunk list was the least reliable posture index (ϕ=0.45). The MDC90 values ranged from 2.6 to 10.3° for angular measurements and from 8.4 to 35.1 mm for linear measurements. The present study demonstrates that most posture indices, especially the trunk posture indices, are reproducible in time among adolescents with IS and provides reference values. Clinicians and researchers can use these reference values to assess change in posture over time attributable to treatment effectiveness.