Global rotations of the cervical spine during arm flexion

Abstract

Anatomical and biomechanical studies showed that total maximal arm flexion was limited to 150°, nevertheless an asymptomatic subject is able to raise his arm up to the vertical. Some studies highlighted that arm flexion involved trunk 3D rotations, but no study has yet assessed with accuracy the kinematics of the cervical spine during arm flexion. The aim of the present study is thus to evaluate the 3D head rotations during arm flexion in asymptomatic subjects. Observational study: 3D head and trunk rotations were assessed in ten healthy, right handed subjects during maximal unilateral left arm flexion using a Polhemus Fastrak electromagnetic device. The 3D rotations were measured at 30°, 90°, 140° of maximal active and passive arm flexion, respectively. 3D rotations at the different levels of arm flexion and for active and passive conditions were compared using Bayesian ANOVA. Head and trunk rotations increased with active and passive arm flexion. Head and trunk kinematic patterns were opposite at maximal arm flexion: relative to the trunk, the head 3D rotations showed flexion, ipsilateral bending and contralateral axial rotation whereas trunk was in extension, contralateral lateral bending and ipsilateral axial rotation. Compared to passive condition, active maximal arm flexion involved significant less head and trunk lateral bending and axial rotation, consequently, the head orientation was better stabilized in space. Maximal arm flexion involves a kinematic pattern of 3D head rotations opposite to the kinematic pattern of 3D trunk rotations. The rotations in the cervical spine could either be a way to compensate trunk rotations in order to maintain the orientation of the head supporting horizontal gaze and/or the result of the synergic organization of movement by the central nervous system.