Three-Dimensional Glenohumeral Joint Kinematic Analyses from Asynchronous Biplane Fluoroscopy Using an Interpolation Technique

Biplane 3D–2D registration approaches have been used for measuring three-dimensional (3D), in vivo glenohumeral joint kinematics. However, in clinical biplane systems, the X-ray images are acquired asynchronously, which introduces registration errors. The present study introduces an interpolation algorithm to improve the accuracy of image registration by generating synchronous fluoroscopy images. Radiostereometric analysis (RSA) was used to validate the interpolation technique for measuring glenohumeral joint kinematics. Our results show that the interpolated-synchronous biplane registration produces more accurate results than asynchronous biplane registration for shoulder kinematics. In comparison to RSA, the mean absolute kinematic error for the humerus was 0.18 mm and 0.4°; for the scapula, the error was 0.25 mm and 0.17°. The results of the interpolated-synchronous biplane registration are in the range of published results of other studies that have validated the 3D–2D registration technique at the shoulder using custom biplane (synchronous biplane) fluoroscopes. This approach will be particularly useful for improving the kinematic accuracy of high velocity activities using clinically available scanners.