The scapular contribution to the amplitude of shoulder external rotation on throwing athletes

Abstract

Traditional clinical testing of the shoulder ER imposes a fixed scapula in order to assess the glenohumeral joint, despite the recognized importance of the scapular mobility and stability on shoulder function. Here the scapular contribution to the amplitude of humeral axial rotation (internal and external) was tested on the dominant shoulder of two groups of 12 subjects, the thrower athletes and the non-athletes group. The scapular 3D position recorded at the end-range of GH and TH IR and ER rotations was compared across groups using a mixed-model twoway ANOVA. At the end-range of humeral ER, throwers showed less GH and TH amplitude and a scapula more in retraction. A positive correlation was found between scapular spinal tilt and TH and GH angles at the end-range of ER. The throwers group showed a scapula more in retraction in maximal external rotation of the humerus, and less external rotation in active motion. On volleyball players, the scapula assumed a position of posterior spinal tilt when the humerus was positioned more in external rotation. No such correlation was found in the control group or the handball players group, possibly due to sports adaptation.