Background: Intertrochanteric fracture is associated with severe morbidity and mortality. The results of postoperative implant failure are catastrophic. The aim of this study was to determine risk factors for implant failure in intertrochanteric fractures treated with proximal femoral nail anti-rotation (PFNA–II) through the assessment of early therapeutic effects.Methods: A single-center retrospective study was conducted on a continuous series of 123 intertrochanteric fracture patients treated

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... with PFNA-II between Dec 2018 and Oct 2019. Perioperative medical and imaging data were collected. The patients were divided into two groups according to whether implant failure of not. The differences in reduction quality, nail length and tip apex distance (TAD) were analyzed to determine the risk factors of implant failure.Results: A total of 80 patients were enrolled, with an average age of 80.2 years old. There were 6 patients with implant failure. There was no significant difference in demographic index between the two groups. The reduction quality of failure group was good, accept and poor with each 2 patients, and that of the non-failure group was 35, 35 and 4 patients respectively. The difference of reduction quality between the two groups was statistically significant. The risk of postoperative implant failure in patients with poor reduction quality was 8.75 times that of patients with good and acceptable reduction from the Logistic regression analysis(OR=8.75,95%CI 1.215-62.99). The differences in nail length, ASA and bone quality were not statistically significant. Conclusion: Reduction quality is a risk factor of implant failure in intertrochanteric fractures treated with PFNA-II. Even if the medial femoral cortex is anatomically reduced, there will be a triangular void area between the nail and the medial femur, which are prone to coxa vara and implant failure. Therefore, good reduction is the key to treat intertrochanteric fracture.