Elucidating the scapulo-humeral rhythm calculation: 3D joint contribution method

Abstract

The scapulo-humeral rhythm quantifies shoulder joint coordination during arm elevation. The common method calculates a ratio of gleno-humeral (GH) elevation to scapulo-thoracic upward rotation angles. However the other rotations also contribute to arm elevation. The objective is to propose a 3D dynamic scapulo-humeral rhythm calculation method including all rotations of the shoulder joints and compare with the common method. Twenty-nine skin markers were placed on the trunk and dominant arm of 14 healthy males to measure shoulder kinematics. Two-way repeated measures ANOVAs were applied to compare the two methods of calculation of joint contributions and scapulo-humeral rhythm during arm elevation. Significant main effects (p < 0.05) were observed between methods in joint contribution angles and scapulo-humeral rhythms. A systematic overestimation of the GH contribution was observed when only using the GH elevation angle because the scapula is moved outside a vertical plane. Hence, the proposed 3D method to calculate the scapulo-humeral rhythm allows an improved functional shoulder evaluation.

Scapulohumeral rhythm in young tennis players

“…In the literature, the scapulohumeral rhythm varies between 1.25:1 and 7.9:1 (Hosseinimehr et al, 2015;Robert-Lachaine et al, 2015). The SHR calculated in our population was in this range except at the 30° of elevation in lowering of the arm.…”

“…The SHR calculated in our population was in this range except at the 30° of elevation in lowering of the arm. However, a large inter-subject variability was found at this low angle (Robert-Lachaine et al, 2015). In our population of young competitive CONTACT B. gillet benoit.gillet@univ-lyon1.fr…”

“…It may then explain the lack of significant difference in SHR. Furthermore, although the 2D-method is reliable to calculate the SHR, other methods (3D) are more accurate (Robert-Lachaine et al, 2015). Nevertheless, this study is the first to analyse the scapulohumeral rhythm in young competitive tennis players and showed that the dominant and nondominant arm present similar characteristics during rising and lowering of the arm.…”

Shoulder Coordination During Full-Can and Empty-Can Rehabilitation Exercises

“…Another concern is the influence of the motion direction. Whereas investigators often focus on upper extremity raising, 6,21,22 it remains unclear why scapular dyskinesis is more easily detected on clinical examination during the lowering phase. 23 Some researchers [24][25][26] have shown similar patterns in the kinematics of the 2 phases.…”

“…The SHR corresponds to the ratio of the glenohumeral (GH) contribution over the scapulothoracic (ST) contribution, where the angular contribution represents the amount of upper extremity elevation that a joint achieves. 6 Patients with rotator cuff tears compensate for the loss of GH motion with more ST motion. 3 Similarly, patients with frozen shoulder or GH osteoarthritis increase their ST upward rotation to achieve upper extremity elevation.…”