Internal Fixation of Displaced Proximal Humeral Fractures: the Effect of Bone Mineral Density and Screw Placement

Introduction: Approximately 15 to 20 percent of all proximal humeral fractures are displaced and require operative treatment [1]. Reduced bone quality of the humeral head complicates internal fixation and may result in implant loosening, fracture re-displacement and poor functional outcome for the patient [2, 3]. Little is known about the effect of bone mineral density (BMD) on internal fixation of proximal humeral fractures. In a previous study, no correlation was found between total BMD determined by dual-energy Xray absorptiometry (DEXA) and the strength of figure-of-eight wiring supplemented with Ender rods [3]. The two-dimensional DEXA technique does not allow for separation between trabecular and cortical BMD. In particular, trabecular BMD might be an important predictor of fixation strength of cancellous screws or blade plates in internal fixation. Therefore, a more extensive analysis of trabecular BMD is needed to identify locations that provide stronger internal fixation of proximal humeral fractures. The objectives of this study were twofold. First, to investigate the threedimensional distribution of trabecular BMD in the humeral head using peripheral quantitative computed tomography (pQCT). Second, to determine the effect of trabecular BMD on the pullout strength of cancellous screws, often used for internal fixation of humeral fractures. We hypothesized that trabecular BMD significantly influences the pullout strength of cancellous screws.