Fig. 1

An 87-year-old woman with trochanteric femur fracture that treated by closed reduction and cephalomedullary nail fixation. a The fracture type was classified as 2018 AO/OTA 31A1.2. b–d Immediate postoperative fluoroscopy in AP, lateral, and anteromedial oblique views showed a good reduction quality, with smooth anteromedial cortex apposition (neutral relation). e Postoperative 3D CT image showed loss of cortical contact at anteromedial inferior corner. The proximal neck was sagged posteriorly into the distal medullary canal (the red arrow). f, g Follow-up X-ray in 6 months. AP view showed the backout of the helical blade by over-sliding, and lateral view showed loss of cortical contact of the anterior cortex with posterior sagging. The red arrow indicates anterior swing of the nail; the yellow arrow indicates negative anteromedial cortex relation, thus a sagittal pendulum-like movement was happened with lower filing ratio of distal nail/canal diameter