Defining optimal calcar screw positioning in proximal humerus fracture fixation

Background Anatomic reduction and placement of an inferior calcar screw are strategies to prevent fixation failure in proximal humerus factures. Optimal position of the calcar screw remains unknown. Methods There were 168 shoulders (68.5% female; average age, 63.6 ± 11.5 years) that underwent open reduction and internal fixation of a displaced proximal humerus fracture involving the surgical or anatomic neck. Univariate and multivariate analyses were performed on preoperative clinical, preoperative radiographic, and postoperative radiographic variables to determine association with fixation failure. A receiver operating characteristic curve was performed to determine a maximum distance from the inferior screw to the calcar (“calcar distance”) as well as a maximum ratio of this distance and the head diameter (“calcar ratio”). Results There were 26 of 168 (15.5%) patients with radiographic failures (19 related to fixation failure). Univariate analysis and multivariate analyses found quality of reduction (P <.001), calcar distance (P <.001), and calcar ratio (P <.001) to be significantly associated with radiographic success. In all patients, receiver operating characteristic analysis found quantifiable thresholds of 12 mm or within the bottom 25% of the humeral head as measures to prevent fixation failure. Conclusions Quality of reduction, calcar distance, and calcar ratio independently correlated with fixation failure. This study provides optimal distances and ratios for calcar screw placement that can be used clinically.