Barrett, Ian R.

Objectives: To validate a neck-shaft angle (NSA) correction formula using the known angle between the medullary nail and lag screw of an indwelling cephalomedullary nail (CMN). Methods: Pertrochanteric femur fractures were created in 7 synthetic femurs and reconstructed with a CMN. Anteroposterior x-rays were taken with the proximal femur in 0, 15, 30, and 45 degrees of internal/external rotation and 10 and 20 degrees of flexion with neutral rotation. The femoral NSA and the nail angle were measured on anteroposterior x-rays. The corrected NSA was obtained by multiplying the known nail angle by the quotient of the measured NSA over the measured nail angle. Results: With increasing degrees of internal or external rotation, the difference between the actual and the measured NSA increased. After correction using the known angle of the nail, the measured NSA was reduced to within 3 degrees of the actual NSA over all degrees of rotation. At neutral rotation, 15 degrees of external rotation, and 10 and 20 degrees of hip flexion, there was minimal difference between the actual NSA and the measured NSA, negating the effect of the correction formula. Conclusions: The measured NSA after CMN of intertrochanteric fractures is altered by hip rotation. This study validates the correction formula, which determines this difference by using the known angle between the lag screw and the nail.

Objectives: To determine whether fixation of pertrochanteric hip fractures with cephalomedullary nails (CMNs) with a neck-shaft angle (NSA) less than the native NSA affects reduction and lag screw cutout. Design: Retrospective comparative study. Setting: Level I trauma center. Patients/Participants: Patients treated with a CMN for unstable pertrochanteric femur fractures (OTA/AO 31-A2.2 and 31-A2.3) between 2005 and 2014. Intervention: CMN fixation. Main Outcome Measurement: NSA reduction and lag screw cutout. Results: Patients fixed with a nail angle less than their native NSA were less likely to have good reductions [17% vs. 60%, 95% confidence interval (CI), −63% to −18%; P = 0.0005], secondary to more varus reductions (41% vs. 10%, 95% CI, 9%–46%; P = 0.01) and more fractures with ≥4 mm of displacement (63% vs. 35%, 95% CI, 3%–49%; P = 0.03). The cutout was not associated with the use of a nail angle less than the native NSA (60% vs. 76%, 95% CI, −56% to 18%; P = 0.5), varus reductions (60% vs. 32%, 95% CI, −13% to 62%; P = 0.3), or poor reductions (20% vs. 17%, 95% CI, −24% to 44%; P = 1.0). Conclusions: The fixation of unstable pertrochanteric hip fractures with a nail angle less than the native NSA was associated with more varus reductions and fracture displacement but did not affect the lag screw cutout. Level of Evidence: Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.