Intra-rater and inter-rater reliability of the fixed plumb line for postural and scoliosis assessment in the sagittal plane: a pilot study.

Background: The plumb line (PL) is a common tool for assessing the sagittal curvatures of the spine, but its accuracy depends on the ability of the physician to use it correctly. This study aimed to present a fixed plumb line (FPL) no longer held by a physician but fixed to a support, evaluating the reliability in posture assessment, comparing it with PL in both adolescent with and without scoliosis.

Methods: The study evaluated the sagittal distances of the spine using a PL and a FPL in 80 young adults aged between 28.7 ± 7.2 and 55 adolescents aged between 12.4 ± 2.3, with and without scoliosis. Two expert and two novice clinicians tested the patients to evaluate the intra-rater and inter-rater reliability of FPL. Each clinician assessed participants twice on the same day, with a predetermined time interval (>1 h) to reduce recall bias. Multi-factor multivariate analysis of variance and two-way analysis of variance assessed the statistical significance, while intraclass correlation coefficient (ICC), standard error of measurement (SEM) and minimum detectable change (MDC) validated FPL consistency.

Results: FPL provided an ICC coefficient >0.90 for all the measures, while PL an average of 0.70. On AIS patients, PL and FPL showed a significant difference for C7  < 0.001 and T12  < 0.001. The measured parameters were sensitive to gender and age for the FPL, furthermore, the C7 and L3 measurements were statistically different between PL and FPL ( < 0.001). Intra-rater reliability results for FPL ranged from 0.94 to 0.98 across various parameters, while the SEM and MDC values underscore the valuable precision of the FPL with changes exceeding 1 cm being meaningful. These findings suggest that FPL could be a reliable and accurate tool for measuring sagittal distances of the spine in both scoliotic and non-scoliotic patients.