A Safe Medial Column Screw Strategy for Transcondylar Humerus Fractures in the Elderly: CT-Based Analysis of Screw Diameter and Insertion Trajectory.

BACKGROUND: Double-plate fixation is widely used for transcondylar fractures of the distal humerus in elderly patients. Recently, fixation using a medial column screw (MCS) without a medial plate has been reported. However, anatomical data regarding optimal screw diameter and insertion trajectories are scarce. This study aimed to clarify the anatomical basis of MCS fixation using CT-based morphologic analysis.

METHODS: We retrospectively analyzed CT data from 92 humeri (51 male, 41 female) obtained between 2012 and 2023. A virtual cylinder was placed along the medial column, and the maximum diameter without cortical breach and insertion angles relative to the humeral axis were measured. Measurement reliability was assessed using intraclass correlation coefficients (ICC), and factors associated with cylinder diameter were assessed using multiple linear regression.

RESULTS: The overall mean cylinder diameter was 6.4 mm ( 95% CI, 6.1-6.7 mm) and was significantly larger in males than in females (P < .001), with no significant age-related difference. Among humeri from individuals aged ≥ 65 years, 25 of 26 (96.2%) accommodated a cylinder diameter of at least 5.0 mm; the observed minimum diameter was 6.0 mm in males and 4.0 mm in females. Sex, age, and body weight were independently associated with cylinder diameter, whereas height was not. Mean insertion angles were 12° axial, 9° sagittal, and 33° coronal. Intraobserver and interobserver ICC values for diameter were 0.86 and 0.67, respectively, whereas those for insertion angles were lower.

CONCLUSION: The medial column anatomically accommodated a diameter of at least 5.0 mm in most elderly patients. An approximately 5.0-mm MCS may therefore represent a candidate diameter when individual anatomy permits, although insertion trajectories require patient-specific adjustment and biomechanical validation is needed.