Defining the flexion-extension axis of the ulna: implications for intra-operative elbow alignment

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.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12891-022-05102-5.

Motion-derived coordinate systems reduce inter-subject variability of elbow flexion kinematics

The selection of a joint coordinate system affects the outcome of motion pathways. We developed coordinate systems for the ulna and humerus, which are generated from upper extremity motion. These Motion-Derived Coordinate Systems (CS) were compared to traditional Anatomy-Derived CS created using surface digitizations of anatomical features. Within-subject repeatability of creating Motion-Derived CS was quantified. In vitro elbow flexion was generated in the gravity-dependent position using an active upper extremity motion simulator. Kinematic pathways of those motions were calculated in terms of valgus angulation and internal rotation of the ulna relative to the humerus, using both CS. The method of creating Motion-Derived CS was highly repeatable-less than 0.5 mm and 1° for all coordinate directions measured. Inter-subject variability of active flexion pathways was reduced with Motion-Derived CS compared to Anatomy-Derived CS (p < 0.05). The decrease in inter-subject kinematic variability when using Motion-Derived CS may increase the statistical power of biomechanical studies and allow for reduced sample sizes. This minimally invasive method, which also determines the elbow flexion and forearm rotation axes and center of the capitellum, may also be applicable in computer-navigated surgery of the upper limb.