An in vivo study of the primary and coupled rotations of the thoracic spine

OBJECTIVE: To provide preliminary data on three-dimensional thoracic spine kinematics measured in vivo. DESIGN: This study measured the three planes of thoracic spine motion in normal subjects using an external measuring device. BACKGROUND: Few studies have investigated the primary and associated coupled rotations in the thoracic spine in vivo. Most knowledge of motion characteristics comes from in vitro studies which have limitations. There is a lack of agreement on the patterns of thoracic coupled motion especially that between lateral flexion and axial rotation. METHODS: Thoracic motion was examined in 60 normal subjects (30 males, 30 females) aged 18-24 years. The primary and coupled rotations of the thoracic regions T(1-4), T(4-8), T(8-12) were measured using a 3 SPACE Fastrak system. RESULTS: The three thoracic regions displayed the characteristic variations in range and distribution of primary rotations previously described. The pattern of coupled motion varied between subjects but an ipsilateral pattern predominated between lateral flexion and axial rotation in the middle and lower thoracic regions while the upper thoracic region was found to exhibit either a contralateral or ipsilateral pattern. Gender did not influence results. CONCLUSIONS: The pattern of coupled motion in the thoracic spine demonstrated some variability between subjects in vivo. Lateral flexion and axial rotation were strongly coupled with overall, their relationship being predominantly ipsilateral.