The Femoral Neck-Shaft Offset: A Key Element in the Reconstruction of Intertrochanteric Fracture.

Background: Anteromedial cortex reduction and accurate placement of the cephalomedullary nail is the key point to confront implant failure of intertrochanteric fractures. Existing intramedullary nails cannot compensate for femoral neck-shaft offset (FNSO), potentially undermining surgical outcome. This study aimed to investigate the effect of FNSO on anteromedial cortex reduction and accurate placement of the cephalomedullary nail for intertrochanteric fractures.

Methods: This retrospective study included patients with intertrochanteric fractures treated with short intramedullary nails at our institution from January 2014 to December 2016, who were divided into acceptable and unacceptable groups according to the anteromedial cortex reduction quality. We measured the femoral neck-shaft offset (FNSO) and offset angle (FNSOA) on the uninjured femur CT. Postoperative CT of the fractured femur was used to measure the offset between the femoral neck axis and the cephalic nail axis (FNCO) and the corresponding angular offset (FNCOA). Cephalic nail insertion alignment was classified into three types (oblique-forward/rear, coincident, and oblique-backward/front) based on FNCO/FNCOA values. Group differences were analyzed, and logistic regression identified predictors of poor reduction.

Results: Fifty-seven patients (mean age 78.10 ± 13.47 years; 74% women) were included. The median FNSO and FNSOA of unaffected femurs were 4.31 (IQR 1.50) mm and 4.85° (IQR 2.01). 42.1% of cases had acceptable anteromedial reduction, while 57.9% were unacceptable. Cephalic nail insertion types were: 43.9% oblique-backward/front, 28.1% coincident, and 28.1% oblique-forward/rear. The unacceptable reduction group had significantly different FNCO (-2.32 vs. 2.14 mm) and FNCOA (-3.5° vs. 0°) compared to the acceptable group (both p < 0.001), despite similar fracture types and devices. Cephalic nail insertion type differed between groups (p < 0.001): oblique-backward/front and coincident insertions were more common in poor reductions. Logistic regression showed that oblique-backward/front insertion (OR = 51.33, 95% CI 7.60-346.85) and coincident insertion (OR = 9.00, 95% CI 1.52-53.40) were strong independent predictors of unacceptable reduction (both p < 0.001). Among insertion types, oblique-forward/rear had the lowest median FNCO (3.59 mm) and FNCOA (0.69°) and only 12.5% unacceptable reductions, versus coincident (0 mm, 0°, 56.3%) and oblique-backward/front (-3.06 mm, -5.84°, 88.0%) (p < 0.001).

Conclusions: It is difficult for existing intramedullary nails to achieve both the reduction of the anterior medial cortex and the accurate implantation of intramedullary nails due to the presence of FNSO. Optimizing intramedullary nailing design and surgical strategy according to FNSO may improve the treatment outcome of intertrochanteric fractures.