The dynamic rotation axis of ulnohumeral joint during active flexion-extension: an in vivo 4-dimensional computed tomography analysis.

Background: As the collateral ligament reconstruction becomes more common to perform, the knowledge between the collateral ligament reconstruction and the elbow rotation axis is still ambiguous. The purpose of this study was to investigate the location of the intersections between the elbow rotation axis and medial and lateral aspect of the humerus.

Methods: Four-dimensional computed tomography (4D CT) scan was designed to obtain the images from 8 participants. The instantaneous rotation axis was created according to the trochlea notch of the ulna in the Rapidform XO software. Then the intersections between the instantaneous rotation axis and the medial and lateral aspect of the humerus were identified in the Geomagic Wrap software. Landmark coordinate systems of the distal humerus was created.

Result: The intersections in the medial aspect of the humerus were mostly located in the superior and posterior quadrant and showed the trend from anterior-superior to posterior-superior with the increment of the elbow flexion. The intersections in the lateral aspect of the humerus were mostly located in the middle half of the anterior quadrant and showed the trend from posterior-inferior to anterior-superior with the increment of the elbow flexion.

Conclusion: There's no isometric point for medial collateral ligament (MCL) and lateral ulnar collateral ligament (LUCL) reconstruction. The isometric area for MCL reconstruction should be considered at the superior and posterior quadrant of the medial aspect of the humerus. The isometric area for LUCL reconstruction should be considered at the middle half of the anterior quadrant of the lateral aspect of the humerus.

Trial Registration: This work was supported by the National Natural Science Foundation of China [ No.81911540488 ] in 07/01/2019.