Soft tissue artefact in the thoracic spine during axial rotation and arm elevation using ultrasound imaging: a descriptive study.

Much of the current understanding of thoracic motion analysis is based on the use of skin sensors or markers. Skin tissue artefact, movement occurring between the skin and underlying bone, is readily acknowledged by researchers as a source or measurement error, yet to date has not been quantified. The aim of this study was therefore to evaluate skin tissue artefact, during thoracic axial rotation and single arm elevation. Using an ultrasound imaging technique this study describes soft tissue artefact in the thoracic spine during axial rotation and single arm elevation in sitting using 30 asymptomatic individuals. The findings from this study indicate that soft tissue artefact (STA) in the mid thoracic region ranges between 14 and 16 mm for 35-degrees of rotation. During single arm elevation 0.8-1.5 mm STA was measured at the levels of T1-T6-T12. The results of this study suggests that STA is a considerable and variable source of error in all regions of the thoracic spine, but most notably for the mid thoracic region during axial rotation.