A morphovolumetric study of head malposition in proximal humeral fractures based on 3-dimensional computed tomography scans: the control volume theory

This study regards a volumetric analysis of proximal humeral fractures. The main purpose was to investigate the head displacement in relation to the shaft and its link to volume reductions (“bone loss”) of the anatomic segments interposed between the head and the shaft: the tuberosities and the calcar. We call this area “control volume.” In 20 fractures, we used 3-dimensional virtual reconstruction to create a reference system that divides geometrically the control volume and allows the evaluation of displacement angles of the humeral head. We calculated the volumetric reduction of control volume segments for each fracture through a specific mathematical protocol. The measurement of the head displacement angles in 20 fractures led to following results: in the coronal plane, 10 varus, 6 valgus, 4 neutral; in the sagittal plane, 6 anterior tilt, 9 posterior tilt, 5 neutral position. There was a reduction of control volume in 19 of 20 fractures. Only in 1 fracture was the control volume intact and the fracture was nonimpacted. In 19 impacted fractures, the volume reduction was variable (4% minimum loss, 98% maximum loss). In head varus position, loss was greater in the medial area than in the lateral area. There was generally a clear correspondence between the positions assumed by the head and the volumetric losses of the respective control volume segments. The control volume is an important anatomic and functional area of the proximal humerus. A morphovolumetric 3-dimensional approach improves knowledge about pathomorphology of proximal humeral fractures.