Measuring The Femoral Neck Anteversion Using Oblique Axial Femoral Neck CT Reconstructions

Objectives: The femoral neck anteversion angle(FNA) is the angle between the axis of the femoral neck(cervical plane) and the coronal plane of the femoral condyles(condylar plane) [1]. If the femoral neck inclines anterior to the condylar plane, the angle of torsion is called anteversion. Conversely, if it directed posterior to the condylar plane, it is called retroversion. FNA measurement is commonly applied in studying congenital dislocation of the hip, slipped capital femoral epiphysis, risk of osteoarthritis, femoral neck fracture, and instability of the hip. It is also used for diagnosing paediatric in-toeing or out-toeing gait, as well as for surgical planning for derotation osteotomy of the femur and total hip replacement [2]. Accurate measurement of the angle is critical when surgical treatment is contemplated.Many methods have been described for measuring femoral anteversion such as biplanar [3] and axial roentgenography [4], 45-degree radiographic method [2], ultrasound [5], and even MRI [6] and computed tomography method [7]. Currently, it is widely agreed that CT provides the most accurate measurement of femoral torsion angle [8]. But any evaluation of the FNA depends on the accuracy of the location femoral neck axis. Various CT methods have been described to locate the femoral neck axis based on a single CT image or two superposed images. Hernandez [7] and Weiner [9] prescribed popular methods to define the femoral neck axis which determined the femoral neck axial directly through a single CT section. Whereas, Reikeras [10] defined the neck axis by two overlapped images of the femoral head and neck. However, in a single CT section the femoral neck and femoral head cannot be observed simultaneously, hence measurement error is almost inevitable. The main aim of this paper was to describe a novel method to measure the FNA through directly femur neck axis by CT reconstruction. The results obtained were statiscally analysed.Methods: Ninety patients were involved in the study, including 36 females and 54 males with a mean age of 45.49 years(range, 14~87 years). CT scan was performed on left femurs of 60 patients and right femurs of the rest 30 patients. And the FNA were measured by observer using femoral neck axial CT reconstruction method.Results: Femoral anteversion can be measured with CT reconstruction accurately. The mean value was 17.53 deg on the right side and 18.64 deg for the left side femora with a standard deviation of 8.17 and 8.17. The mean value of male type bones was 17.85 deg and 18.89 deg of female type bones with a standard devation of 7.91 and 8.55. The mean FNA of women is slightly larger than men, and the mean FNA of left is slightly larger than right, but both of the differences are not statistically significant. The mean FNA of youth group was 25.96±6.35 deg. The mean value of middle-aged group was 15.5 deg and 13.35 deg for the old group.Conclusion: Femur neck axis CT reconstruction method could be applied to measure FNA accurately. FNA has no significant statistically differences in gender and side. Femoral neck anteversion angle was decreased along with the age increases.