To investigate the morphological characteristics of cortical support reduction cephalomedullary nailing in intertrochanteric hip fractures, and to provide a reference for further study of cortical buttress reduction theory.

From January 2020 to June 2022, aretrospective study was conducted on 72 patients treated with short femoral cephalomedullary nails for intertrochanteric fracturesin our hospital, including 25 males and 47 females, who had complete 3D-CT imaging data and obtained cortical supportreduction. The average age is 82.8 years old, ranging from 65 to 99 years old. According to the AO/OTA classification in 2007, 21 cases were of type 31-A1 and 51 cases were of type 31-A2. The cortical contact morphology between the head-neck fragment and the proximalfemoral shaft was observed by 3D-CT after operation, and it was divided into three types: the cuspof head-neck fragmentvs. the medial cortex of proximalfemoral shaft, the cuspvs. The anteromedial angle, and the anterior cortex vs. the anterior cortex. Through the postoperative 3D-CT rotation stereoscopic observation, the rotation ofhead-neck fragmentsare divided into three types: no rotation, flexion rotation and hyperextension rotation, and measure the rotation angles.

There were 14 cases of cusp vs. medial cortex, 51 cases of cusp vs. anteromedial angle and 7 cases of anterior cortex vs. anterior cortex in cortical supportreduction, accounting for 19.5%, 70.8% and 9.7% respectively. Chi square test was performed for three types, χ²=20.850 (P<0.01). It showed that the rotation types of head-neck fragmentwere different from the morphology of cortical support.The most common shape of head-neck fragment rotation in the three types was flexion rotation, with 57 cases (79.2%) in total. The rotation angles were (13.1±5.3) °, (15.0±5.2) ° and (18.5±8.8) °, respectively. ANOVA F=1.073 (P>0.05), indicating that the rotation angles of the three types of flexion positions were the same.

Cortical support reduction of intertrochanteric fractureis mostly functional reduction. The common morphological feature is that the cusp of head-neck fragment is in the forward flexion position and contacts with the anteromedial angle of the femoral shaft.