Objective:To discuss the displacement characteristics of Garden type III femoral neck fracture and investigate the reliability, validity and clinical value of the frontal Garden index in assessing the displacement degree of Garden type III femoral neck fracture.Methods:The pelvis X-ray films of 98 patients with Garden type III femoral neck fracture treated at Luoyang Orthopedic-Traumatological Hospital of Henan Province (Henan Provincial Orthopedic Hospital) from October 2010 to October 2018 were collected, including 47 males and 51 females; aged 19-89 years [(64.9±16.2) years]. Three-dimensional data of the hip with 64-slice CT were available in 21 patients. Each patient′s frontal Garden index was measured three times by three senior doctors, which was repeated twice in turn. The distribution characteristics of the frontal Garden index were statistically described. The reliability of the frontal Garden index was tested by Spearman correlation coefficient and Kappa coefficient, including test-retest reliability and intra-rater consistency. The contact area of fracture ends and upper-shift distance of the femoral neck were calculated based on three-dimensional CT data of the hip in 21 patients. Correlation analysis of the contact area of fracture ends and upper-shift distance of the femoral neck with the frontal Garden index was performed by multiple correlation analysis to assess the validity of the frontal Garden index.Results:The Frontal Garden index of 98 patients with Garden type III femoral neck fracture was (136±15) °, with the minimum value of 90 ° and maximum value of 159 °, and was found to be normally distributed ( P>0.05). Spearman correlation coefficient of the test-retest reliability was 0.93, 0.97 and 0.95, respectively (all P<0.01). Kappa coefficient of the intra-rater consistency was 0.87, 0.91 and 0.86, respectively (all P<0.01). The frontal Garden index was positively correlated with the contact area of fracture ends ( r=0.80, P<0.01), and was negatively with the upper-shift distance of the femoral neck ( r=-0.77, P<0.01). Conclusions:The displacement degree of Garden type III femoral neck fracture shows diversity and normal distribution. The frontal Garden index can credibly and effectively measure the displacement degree of Garden type III femoral neck fracture, which may help to choose the treatment plan.