Evaluating proximal ulnar morphology in relation to the humeral flexion–extension axis

Abstract

Background

The study aimed to evaluate the 3D relationship between the plane of the posterior surface of the olecranon, a newly defined plane through the ridge of the greater sigmoid notch (GSN), and the ulno-humeral flexion–extension axis (FE axis), respectively.

Methods

Twenty-four healthy left elbows were computed tomography scanned and 3D-segmented. First, a Cartesian ulnar coordinate system (UCS) was determined. Next, several anatomical landmarks were identified. The UCS and landmarks were assessed for repeatability and reproducibility. The orientation of the posterior surface and the plane through the GSN was evaluated relative to the anatomical FE axis.

Results

Both the UCS and the landmarks were considered repeatable and reproducible. In the axial plane, the mean angle between the posterior surface and the FE axis was 3° (standard deviation: ±5°, 95% confidence interval [CI]: [−6°; 12°]) external rotation. The mean axial angle between the GSN and the FE axis was 88° (standard deviation: ±3°, 95% CI: [83°; 94°]) external rotation.

Conclusion

This study concludes that the angulation between the posterior plane surface and the FE axis is highly variable (95% CI range: 18°). The plane through the ridge of the GSN of a healthy proximal ulna could provide a more reliable anatomical landmark to estimate the position of the elbow FE axis compared to the posterior surface (95% CI range: 11°).