Design and Testing of a Dynamic Orthosis to Reduce Glenohumeral Subluxation With Omnidirectional Shoulder Motion

Objective: This paper aimed to develop an orthosis to apply a compensating force to improve the stability of the glenohumeral joint without resisting arm movement. Methods: The proposed orthosis was based on a parallelogram structure to provide a pair of compensating forces to the glenohumeral joint center. Theoretical analysis was used to evaluate the additional moments caused by glenohumeral joint center shifting. Then, an experimental evaluation platform, composed of a torque sensor, a force sensor, and a 3D printed arm, was set up to assess the additional moments and compensating force. Finally, the proposed orthosis was compared with the traditional orthosis to compare the subluxation reduction and the movement restriction when worn by stroke patients. Results: There was only a maximum additional moment of 0.87 Nm for the glenohumeral center shifting. During 3D printed arm movement, the moment correlation coefficient between with and without the proposed orthosis was greater than 0.98, and the compensating force was larger than 90% of the arm weight. The proposed orthosis reduced subluxation by $12.5\pm 3.5$ mm, and the traditional orthosis reduced subluxation by $7.7\pm 2.2$ mm, indicating that the subluxation reduction of the proposed orthosis was more effective ($p< 0.001$). Meanwhile, the proposed orthosis's motion restriction joint was significantly smaller than traditional orthosis ($p< 0.001$). Conclusion: The proposed orthosis provided sufficient gravity compensation without resisting arm movement. Significance: The proposed orthosis can improve the shoulder's stability during shoulder movement, potentially improving the rehabilitation effect of patients with shoulder subluxation.