A new in vivo technique for three-dimensional shoulder kinematics analysis

Objective. The field of shoulder kinematics research has long relied upon the use of cadaveric models or invasive techniques in human volunteers. In this paper, a novel method is presented that utilizes magnetic resonance imaging (MRI) and a software system called 3DVEWNIX. This method permits non-invasive, repetitive evaluation of living patients for glenohumeral kinematics analysis. The objectives of this study were twofold: to validate the quantitative accuracy of this technique; and to demonstrate glenohumeral relationships in asymptomatic volunteers during internal and external rotation of the arm. Design. The translational accuracy was first assessed by comparing known cadaveric glenohumeral translations with calculations from MR images of the cadaver. Nine asymptomatic volunteers were subsequently placed in an external shoulder positioning device in the scanner and imaged in 10° increments of actively achieved internal and external rotation. Three-dimensional reconstructions of the glenoid and humerus were used to evaluate the glenohumeral relationships in the tested positions of rotation. Results. The quantitative analysis revealed an error of 0.61 mm (SEM 0.11 mm). Examination of the volunteers demonstrated normal relationships about the glenohumeral joint in internal and external rotation. In addition, this method provided detailed images of the bony surface architecture from any perspective. These images can be transformed into a cinematic three-dimensional depiction of active shoulder rotation. Conclusion. This new technique offers an accurate, non-invasive method for assessing the normal glenohumeral relationships in shoulder kinematics. We now possess the capability to investigate the kinematics of normal and abnormal shoulder conditions non-invasively in a large patient population.