[Relationship between cortical fragments and avascular necrosis of femoral head in young adult femoral neck fractures based on CT imaging].

Objective: To explore the effect of femoral neck cortical fragments and surfacial area on avascular necrosis(AVN) after internal fixation of femoral neck fractures based on CT imaging in young adult.

Methods: From January 2011 to January 2021, 218 young and middle-aged patients with femoral neck fractures were reverse triangle fixed with three cannulated lag screws, including 104 males and 114 females;aged 19 to 60 years old with a mean of (48.22±10.58) years old. The preoperative waiting time≤48 h was 155 cases, and the preoperative waiting time> 48 h was 63 cases; 68 cases were comminuted cortex of the femoral neck, 32 of them with superficial area of the comminuted cortex>25 mm². All patients were followed up for at least 2 years, the age, gender, injury side, body mass index, injury mechanism, preoperative waiting time, operation time, Garden classification, whether femoral neck cortex fracture and size by CT analysis and complications were analyzed the correlation to the definite occurrence of AVN. The AVN group and the non-AVN group were divided according to the final efficacy results.Univariate analysis yielded significant independent variables, Multiple Logistic regression analysis was further performed to identify the independent risk factors for AVN.

Results: By univariate analysis, the AVN and non-AVN groups were significant in injury mechanism(χ²=18.552, P=0.000), preoperative waiting time( χ²=2.065, P=0.033), Garden classification (χ²=12.598, P=0.006), comminuted cortex (χ²=16.357, P=0.000), and the superficial area of the comminuted cortex(χ²=23.371, 0.000, P=0.000). Multiple Logistic regression indicated injury mechanism high energy injury[Exp(B)=3.487, 95%CI(1.583, 10.464), P=0.002], comminuted cortex of the femoral neck[Exp(B)=2.494, 95%CI(1.315, 10.861), P=0.002];the superficial area of the comminuted cortex>25 mm²[Exp(B)=22.161, 95%CI(3.922, 1242.828), P=0.001] were independent risk factors for AVN after internal fixation of femoral neck fractures.

Conclusion: High energy injury mechanism, with comminuted cortex of the femoral neck and the superficial area of the comminuted cortex> 25 mm² were independent risk factors for AVN.The larger the superficial area of the cortex fragment may suggest more complicated injury mechanism and worse outcome.