Comparison of kinematics of imposed head movements and head movements in free space

Main research question: The correct positioning of the head and neck is essential during electrical wheelchair use. Therefore, proper head support is important for persons with impaired head stabilization and/or positioning. Existing systems often provide only static, fixed head support, while during daily life support of different head support positions and position changes are needed. Therefore, an adaptive, dynamic head support is being developed by the authors. As design input, the kinematics of the head in free space and during imposed and restricted head movements were studied to define the degrees of freedom and movements that the system should be able to support.
Research methods: An observational study (one measurement session) was set up with non-impaired individuals. Besides head movement in free space, imposed passive and restricted active head movements were measured, using a measurement device that allowed the head to rotate around fixed rotation points. Participants performed flexion/extension, lateral rotation, lateral flexion, and a combination of lateral rotation and lateral flexion.
Results: A total of nineteen participants were included in the study. For this abstract, the kinematic data of thirteen participants were studied. In flexion-extension, the rotation was isolated with minimal rotation over the other two axes (< 5 degrees). Lateral rotation showed variable flexion/extension and contralateral lateral flexion at the movement extremes. Lateral flexion showed variable rotations over the other axes. For the imposed head movements, especially in flexion-extension but also in lateral flexion there was a mismatch at the movement extremes in which the head lost contact with the measurement device. In lateral rotation, the head and measurement device followed approximately the same path. However, in the combined trial, together with lateral rotation, the head showed contralateral lateral flexion (10-15 degrees).
Conclusions: The research results provide input for the movement paths to be implemented in the new head support. In order to approximate the head kinematics in free space and to account for user variability, flexion extension, lateral rotation and lateral flexion movements should not be controlled over fixed rotation points. Rotations should be combined and the translations of the biomechanical rotation axes should also be incorporated.