Coupling between 3D displacements and rotations at the glenohumeral joint during dynamic tasks in healthy participants

• The assessment of glenohumeral displacement is mainly limited to static tasks.
• Glenohumeral displacements were measured with an error less than 0.15 mm.
• Significant coupling between glenohumeral displacements and rotations.
• Upward displacement increased up to 12.4 mm with abduction angle during arm elevation.

BackgroundGlenohumeral displacements assessment would help to design shoulder prostheses with physiological arthrokinematics and to establish more biofidelic musculoskeletal models. Though displacements were documented during static tasks, there is little information on their 3D coupling with glenohumeral angle during dynamic tasks. Our objective was to characterize the 3D glenohumeral displacement–rotation couplings during dynamic arm elevations and rotations.MethodsGlenohumeral displacements were measured from trajectories of reflective markers fitted on intracortical pins inserted into the scapula and humerus. Bone geometry was recorded using CT-scan. Only four participants were recruited to the experiment due to its invasiveness. Participants performed dynamic arm abduction, flexion and axial rotations. Linear regressions were performed between glenohumeral displacements and rotations. The pin of the scapula of one participant moved, his data were removed from analysis, and results are based on three participants.FindingsThe measurement error of glenohumeral kinematics was less than 0.15 mm and 0.2°. Maximum glenohumeral displacements were measured along the longitudinal direction and reached up to + 12.4 mm for one participant. Significant couplings were reported especially between longitudinal displacement and rotation in abduction (adjusted R2 up to 0.94).InterpretationThe proposed method provides the potential to investigate glenohumeral kinematics during all kinds of movements. A linear increase of upward displacement during dynamic arm elevation was measured, which contrasts with results based on a series of static poses. The systematic investigation of glenohumeral displacements under dynamic condition may help to provide relevant recommendation for the design of shoulder prosthetic components and musculoskeletal models.