Errors in Shoulder Joint Position Sense Mainly Come from the Glenohumeral Joint

While synchronous movement of the glenohumeral and scapulothoracic joints has been emphasized in previous kinematics studies, most investigations of shoulder joint position sense have treated the shoulder complex as a single joint. The purposes of this study were to investigate the joint position sense errors of the humerothoracic, glenohumeral, and scapulothoracic joints at different elevation angles and to examine whether the errors of the glenohumeral and scapulothoracic joints contribute to the errors of the humerothoracic joint. Fifty-one subjects with healthy shoulders were recruited. Active joint position sense of the humerothoracic, glenohumeral, and scapulothoracic joints was measured at 50°, 70°, and 90° of humerothoracic elevation in the scapular plane. The results showed that while scapulothoracic joint position sense errors were not affected by target angles, there was an angle effect on humerothoracic and glenohumeral errors, with errors decreasing as the target angles approached 90° of elevation. The results of a multiple regression analysis revealed that glenohumeral errors explained most of the variance of the humerothoracic errors and that scapulothoracic errors had a weaker predictive relationship with humerothoracic errors. Therefore, it may be necessary to test scapular joint position sense separately in addition to the assessment of the overall shoulder joint position sense.