Modified calcar ratio for predicting varus collapse in proximal humerus fractures

Introduction Proximal humerus fractures are common, especially in older adults, and often result in complications such as varus collapse after open reduction and internal fixation (ORIF). Despite successful surgical methods, complication rates remain significant, with varus collapse being a primary cause of failure. Ensuring proper screw placement, particularly the calcar screw, is vital to prevent this issue. This study introduces a modified calcar ratio (MCR) that combines two key measurements - tip distance and calcar distance - to predict varus collapse and improve surgical outcomes. Methods This retrospective study analyzed patients treated for proximal humerus fractures from September 2022 to June 2024. Inclusion criteria were adults with 3- or 4-part fractures who underwent ORIF with a proximal humerus plate within two weeks of injury. Preoperative and postoperative radiographs were evaluated to determine fracture classification, reduction quality, and radiological parameters, including MCR. MCR was calculated as the sum of the tip distance and calcar distance divided by the humeral head radius. Statistical analysis, including ROC curve analysis, assessed MCR’s ability to predict varus collapse. Results A total of 108 patients were included. MCR was significantly higher in patients who experienced varus collapse (median MCR: 0.7) compared to those who healed (median MCR: 0.5). Varus collapse occurred in 17.6 % of patients, with a median onset time of 8 weeks post-surgery. Statistical analysis showed a strong correlation between higher MCR and varus collapse, with a sensitivity of 100 % and a specificity of 47 %, at a cut-off point of 0.46 for predicting failure. The ROC curve demonstrated 78 % discriminatory ability for MCR. Conclusion The MCR is a reliable, practical tool for predicting varus collapse following ORIF in proximal humerus fractures. By considering both the tip and calcar distances, MCR provides a single, effective measure to optimize surgical outcomes. An intraoperative MCR value below 0.46 demonstrated high sensitivity for predicting lower risk of varus collapse, and may serve as a useful intraoperative reference.