Unlocking the mechanics of valgus-impacted proximal humeral fractures: A 3D analysis of rotational deformities and tuberosity displacement.

Background: Traditional classifications usually focus on fracture morphology. This study aims to analyse rotational deformities in valgus displaced fractures in a retrospective cohort setup and investigate correlation with tuberosity displacement and glenohumeral alignment. Methods: One hundred and fifty-one three-dimensional (3D) computed tomography (CT) images were analysed. Axis systems were defined in the glenoid, head and diaphysis using Mimics and 3-Matic. Rotational analysis was performed using MATLAB. These were compared to normal values obtained on 87 3D reconstructed CT images of intact shoulders and divided into varus and valgus type, yielding 50 valgus fractures. Statistical analyses included Mann-Whitney U tests and Spearman correlations. Results: Three- and four-part fractures showed significant anteflexion (p = 0.025 and 0.033) and internal rotation (p = 0.004 and 0.004) of head versus glenoid. Two- and three-part fractures showed significant retroflexion of shaft versus head (p = 0.012 and 0.022) whilst four-part fractures showed significant internal rotation of shaft versus head (p = 0.001). A positive correlation was observed between valgus and tuberosity displacement (p < 0.001). Discussion: This highlights the importance of reducing both valgus and head anteflexion, particularly in three- and four-part fractures. Furthermore, there is a correlation between the displacement of the greater and lesser tuberosities and the degree of valgus displacement. Level of evidence: IV.