Stability and intra-tester reliability of an in vivo measurement of thoracic axial rotation using an innovative methodology.

The aim of this study was to evaluate the stability and intra-tester reliability of an innovative approach to measure active thoracic spine axial rotation. Ultrasound imaging of a thoracic vertebra in conjunction with Polhemus motion analysis of the transducer was used to measure axial thoracic spine rotation in a functional position. The range of motion in a convenience sample of asymptomatic subjects (n=24) was calculated across ten repetitions of a single trial to evaluate stability. The protocol was repeated the same day and 7-10 days later to provide data for within and between day intra-tester reliability. Mean total range of axial rotation was 85.15 degrees across a single trial with SD=14.8, CV=17.4, SEM=3.04. SEM ranged 0.63-3.37 for individual subjects and 2.60-3.64 across repetitions. Stability of performance occurred at repetitions 2-4. Intra-tester reliability (ICC(2,1)) was excellent within day (0.89-0.98) and good/excellent between days (0.720.94). Bland-Altman plots however suggest that agreement may range from 0 to 10% for within day measures and from 0 to 15% for between day measures. Whether this combined approach has sufficient precision and accuracy as a clinical research tool has yet to be fully evaluated.