Comparison of functional methods and experimental conditions for the in vivo estimation of the glenohumeral joint centre

The purpose of this research is to test the experimental conditions which lead to the best determination of the glenohumeral joint rotation centre in vivo with two shoulder circumductions (30°,130° abduction) and two relative displacements (humerus with respect to scapula or clavicle). Nine subjects perform circumduction movements of small magnitude. Three functional methods were used to estimate the glenohumeral joint rotation centre: Invariant Point (IP), Helical Axes (HA), Sphere-Fitting (SF), and. The dispersion of the CoR estimated for each method was calculated. The results have proved that the joint rotation centre obtained by each method is significantly different. In circumduction conditions, the distances between CoR estimated are less important for humerus/clavicle than humerus/scapula. For the relative displacement conditions, the distances between CoR estimated are less important for circumduction arm at 30° than circumduction arm at 130°. The results have also revealed that the IP is more reliable than the other calculations as far as the dispersion criterion is concerned. Consequently, the circumduction with the arm at 30° of abduction (rather than 130°) and considering the relative displacement of Humerus vs. Clavicle (rather than Humerus vs. Scapula) seems the more appropriate movement for the functional determination of the Glenohumeral joint centre.