A Neck Orthosis with Multi-Directional Variable Stiffness for Persons with Dropped Head Syndrome

TL;DR

This work tackles DHS, a condition causing forward head posture, by introducing a portable passive neck brace with a compliant elastic-bar mechanism that delivers adjustable sagittal support while preserving rotation. A simple moment-estimation framework and a Belendez-based actuator model link stiffness to the assistive moment, and a prototype integrated into a halo brace demonstrates that the device can unload neck extensor muscles during sagittal flexion without compromising rotational mobility. Mechanical tests show the device can supply up to ~55% of the ideal head-weight moment $BM_{id}$, and EMG data from eight healthy participants show significant SPL reduction under higher stiffness with preserved ROM, supporting the device’s potential clinical benefit for DHS patients. These results suggest a practical, non-invasive balance between support and mobility, warranting clinical evaluation in DHS populations.

Abstract

Dropped Head Syndrome (DHS) causes a passively correctable neck deformation. Currently, there is no wearable orthopedic neck brace to fulfill the needs of persons suffering from DHS. Related works have made progress in this area by creating mobile neck braces that provide head support to mitigate deformation while permitting neck mobility, which enhances user-perceived comfort and quality of life. Specifically, passive designs show great potential for fully functional devices in the short term due to their inherent simplicity and compactness, although achieving suitable support presents some challenges. This work introduces a novel compliant mechanism that provides non-restrictive adjustable support for the neck's anterior and posterior flexion movements while enabling its unconstrained free rotation. The results from the experiments on non-affected persons suggest that the device provides the proposed adjustable support that unloads the muscle groups involved in supporting the head without overloading the antagonist muscle groups. Simultaneously, it was verified that the free rotation is achieved regardless of the stiffness configuration of the device.

Figures (11)

• Figure 1: Illustration of neck mobility with the proposed elastic mechanism and components of the exoskeleton device. The elastic actuator provides a nonrestrictive force that partially compensates the head weight during sagittal flexion relieving the extensor muscles. The assistive force is regulated by adjusting the stiffness of the elastic mechanism.
• Figure 2: Schematic view of the passive actuator and working principle in three sectioned views
• Figure 3: Free Body Diagram showing the forces involved in the interaction between the device and the user.
• Figure 4: Cross section of the 7 actuator's bars in a hexagonal arrangement. The 3 red bars are coupled during the High-Stiffness mode.
• Figure 5: Neck brace components. (a)Body attachment with the passive actuator and slider b) Isolated actuator constituted by the elastic bars inserted in the body attachment. The middle bar connects to the mobile plate at the bottom. c) Head attachment and horizontal rail connected to the vertical slider.