Objective: To evaluate the correlation between the diameter of intramedullary nails used in the surgical treatment of femur, tibia, and humerus shaft fractures and the narrowest portion of the medullary canal as measured on preoperative radiographs.

Materials and Methods: This retrospective study included patients over 18 years old who underwent intramedullary nailing between January 2020 and January 2025. Preoperative anteroposterior and lateral radiographs were assessed to measure the narrowest medullary canal diameter. Nail diameters used during surgery were compared with these measurements.

Results: A total of 162 patients (82 femur, 46 tibia, and 34 humerus fractures) were included. The mean difference between the isthmus and nail diameter was 3 mm for femur, 3.5 mm for tibia, and 2 mm for humerus. A statistically significant positive correlation was found between radiographic canal measurements and the nail diameters used (p<0.05).

Conclusion: A consistent undersizing of nails relative to the isthmus diameter was observed. The results emphasize the importance of preoperative radiographic assessment in ensuring optimal surgical planning and nail selection.