Influence of cephalomedullary nail length and caput–collum–diaphyseal angle on tip–apex distance and early mechanical cut-out in trochanteric femur fractures

Early mechanical cut-out remains one of the most severe complications after cephalomedullary fixation of trochanteric femur fractures. While tip–apex distance (TAD) and lag screw position are well-established predictors, the independent influence of nail length and the caput–collum–diaphyseal (CCD) angle remains unclear. This question is clinically relevant because implant standardisation may constrain screw trajectory in anatomically variable proximal femora and thereby hinder optimal TAD attainment and potentially increase cut-out risk. We retrospectively analysed 373 consecutive, predominantly older adults with AO/OTA 31-A1 to 31-A3 trochanteric femur fractures treated with cephalomedullary nails at a Level I trauma center (2018–2022). Primary outcomes were achievement of TAD < 25 mm and early mechanical cut-out within 90 days. Multivariable logistic regression and Firth-penalised models addressed confounding and rare-event bias. A predefined homogeneous subgroup of AO/OTA 31-A2 fractures with good reduction (Baumgaertner criteria) treated with 130° nails was analysed separately. Contralateral CCD angle and CCD mismatch were assessed where imaging permitted. Cut-out-free survival was analysed using Kaplan–Meier estimates and penalised Cox regression. TAD < 25 mm was achieved in 313/373 (83.9%) and center–center screw position in 324/373 (86.9%). Early cut-out occurred in 16/351 (4.6%), with no events after day 65. Nail length and CCD angle were not independently associated with TAD attainment or cut-out (e.g., nail length OR 1.27, 95% CI 0.55–2.91 for TAD < 25 mm; all p > 0.30). Center–center positioning strongly predicted TAD < 25 mm (OR 14.98, 95% CI 7.35–30.54; p < 0.001) and was associated with lower cut-out risk (OR 0.23, 95% CI 0.09–0.69; p = 0.010). TAD < 25 mm was also associated with lower cut-out risk (OR 0.29, p = 0.026). CCD mismatch was more pronounced in non-130° configurations but was not associated with early cut-out. Within the implants used in this cohort, nail length and CCD angle were not independently associated with TAD attainment or early cut-out. Center–center lag screw placement and achieving TAD < 25 mm were the dominant modifiable intraoperative targets to minimise cut-out risk. Although CCD mismatch did not translate into higher cut-out rates in this cohort, it may still be relevant in atypical anatomies and warrants further study.