Quantitative Analysis of Fracture Line Distribution Using Three-Dimensional Mapping and Its Relationship to Plate Fixation in Intra-articular Distal Humerus Fractures: A Comparison of Young and Older Patients.

Background: The aim of this study was to compare fracture line distribution between younger and older patients with intra-articular distal humerus fractures using three-dimensional mapping and to evaluate whether these differences influence distal fixation options using a tab-equipped posterolateral plate. Methods: A retrospective single-centre observational study was conducted. Surgically treated intra-articular distal humerus fractures between 2012 and 2023 were reviewed. Patients were stratified by age (older, 65 years or older; younger, younger than 65 years). Computed tomography (CT)-based three-dimensional (3D) surface models were virtually reduced, and transverse and longitudinal fracture lines were traced and measured. Posterior orthographic two-dimensional (2D) projections were aligned to a template posterior volume-rendered image. Plate overlay was performed using a posterolateral distal humerus plate with a lateral tab. Results: Sixty-seven cases met the criteria. Transverse fracture lines were more distal and longitudinal lines more lateral in older patients (all p ≤ 0.01). In the plate overlay analysis, support screw non-insertability (p = 0.02) and fracture lines located distal to the level of the tab support screw hole (p < 0.01) were more frequent in older patients. Conclusions: Older patients showed a more distal transverse and more lateral longitudinal fracture line distribution. These patterns may constrain distal lateral fixation options when using a tab-equipped posterolateral plate. Level of Evidence: Level IV (Therapeutic).