Six-degree-of-freedom manikin neck for immobilisation training, incorporating linear potentiometers for real-time motion feedback

Neck immobilisation manoeuvres are performed by clinicians when moving patients with suspected cervical spine injuries and may mitigate further harm to the spinal column and spinal cord. Existing patient simulator manikins (PSM) do not have realistic neck articulations and are not instrumented to provide the user with feedback regarding manikin neck motion. The aim of this study was to design, manufacture, and test a proof-of-concept instrumented and articulated neck for an existing PSM. The neck comprised 3D-printed ball-and-socket articulations with 'intervertebral' motion limiting stoppers and extension springs to provide passive neck stiffness. Aluminium adaptor plates and locking mechanisms were designed to interface the neck with existing attachment points without modification of the existing manikin. A passive Stewart-Gough platform arrangement of linear slide potentiometers and a forward kinematics algorithm were used to measure the pose of the head with respect to the torso. Head angle accuracy, range of motion (ROM) and stiffness were assessed. Optoelectronic motion capture in 3D was used for verification measurements. ROM of the neck for flexion (25.0°), extension (29.3°), left (24.7°) and right (21.0°) lateral bending were limited by the potentiometer assembly, while ROM for left (52.5°) and right (48.4°) axial rotation was limited by the stoppers. Neck stiffness remained low until close to the end of ROM (range 5.8-28.3 Nmm/° across all axes) at which point stiffness increased by up to an order of magnitude (43.4-404.5 Nmm/°). Measured head-to-torso angle had root-mean-squared error less than 0.89° compared to motion capture measurements. The PSM neck prototype demonstrates design elements that enable six-DOF motion, low stiffness and real-time head-neck motion feedback. Adjustments to improve ROM, stiffness variation throughout ROM, anatomical realism and evaluation in paramedic training settings, would be required to implement the prototype in immobilisation training.