1 Patients
Data from 400 patients who underwent CT angiography of lower limbs in the Department of Imaging, Affiliated Hospital of Inner Mongolia Medical University from 2019 to 2021 were collected. All CT data were obtained by GE Lightspeed spiral CT with slice thickness of 0.625 mm, voltage of 120 kV, and current of 100 mA. This study was approved by the Ethics Committee of Inner Mongolia Medical University (YKD202201135).
Inclusion criteria: (1) aged > 30 years; and (2) scanning of the full length of the femur.
Exclusion criteria: (1) poor image quality that affects measurement; and (2) conditions that affect the shape or bone mass of the proximal femoral medullary canal, such as hip deformity, local bone defect, bone tumor, and previous history of hip surgery.
Grouping: A total of 236 samples were finally collected, including 121 males and 115 females, with an average age of 67.66 ± 13.65 years. All persons gave their informed consent prior to their inclusion in the study. The sample was divided into 4 groups according to age: <60 (group A - control), 60–69 (group B), 70–79 (group C), and > 80 years (group D). Both femurs were measured for all patients, and the average was used for comparison.
2 Measurements
Mimics 21.0 software was used to measure 4 anatomical morphological parameters of proximal femur, including FNSA, FNA, FO, and FHD. Comparisons were made between age groups of the same gender and between genders in the same age group to analyze the correlation of anatomical parameters with age and gender. Moreover, the results were compared with previous studies.
2.1 Standard coronal plane is the plane passing through the axes of the femoral neck and the proximal femoral shaft.
2.2 Transverse plane is the plane perpendicular to the longitudinal axis of the femur.
2.3 Femoral offset (FO) is the vertical distance from the center of rotation of the femoral head to the femoral shaft axis.
2.4 Femoral neck-shaft angle (FNSA) is the angle between the axes of the femoral neck and the femoral shaft.
2.5 Femoral neck anteversion (FNA)[7] is the angle between the projection line of the femoral neck axis at the transverse plane of distal femur and the line connecting the posterior poles of the medial and lateral femoral condyle
2.6 Femoral head diameter (FHD) is diameter of a best-fit circle around the femoral head
Methods
1 Measurement method
1.1 Establishment of the basal plane
Image data were imported into Mimics 21.0 (Materialise, Belgium). Next, the Interactive MPR tool under the Along Plane option in the VIEW option was selected to perform multi-planar reconstruction of thin-slice images. The posterior pole of the medial and lateral femoral condyle and the posterior pole of the greater trochanter were found to establish the basal plane, which passed through the posterior pole of the medial and lateral femoral condyle and the posterior pole of the greater trochanter (Fig. 1a).
1.2 Establishment of the transverse plane and femoral neck axis
A transverse plane was established perpendicular to the longitudinal axis of the femoral shaft in the coronal plane parallel to the basal plane (red and blue line in Fig. 1b). The center of the femoral head (denoted as E in Fig. 1d) was found in the transverse plane. The center of the base of the femoral neck (denoted as G in Fig. 1f) was found straight below. FG in Fig. 1f is the femoral neck axis (F in Fig. 1f is the projection of the center of the femoral head in this plane).
1.3 Establishment of standard coronal plane
The sagittal plane (Fig. 1c) was established parallel to the longitudinal axis of the femoral shaft in the basal plane (green line in Fig. 1b). The proximal femoral shaft axis was found in this plane (denoted as D in Fig. 1c). The standard coronal plane (Fig. 1g) was then established using Figs. 1c and 1f, which is through the femoral neck axis and proximal femoral shaft axis.
1.4 Measurement of FNSA, FO and FNA
A circle was drawn at and 2 cm below the lower edge of the lesser trochanter, respectively. The edges of the circles were tangent to the lateral cortex of the femur. The centers of the circles were determined. The axis passing through the two centers is the proximal femoral shaft axis. ∠L in Fig. 1g is FNSA. The line segment HI is FO.
The femoral neck axis was determined. The posterior poles of the medial and lateral femur condyle were then identified at the transverse plane of distal femur (Fig. 1e). The angle between the projection line of the femoral neck axis at the distal femur (red line in Fig. 1h) and the line connecting the posterior poles of the medial and lateral femoral condyle is FNA (∠M in Fig. 1h).
1.5 Measurement of FHD
The maximum diameter of the femur was identified and measured in the transverse, coronal, and sagittal planes, respectively (ST, QR and OP in Fig. 2a, 2b and 2c, receptively). The average of the three measurements, that is, (OP + QR + ST)/3, was taken as the FHD value.
2 Statistical analysis
Data analysis was performed using SPSS 25.0. The data were expressed as mean ± standard deviation (x ± s) and tested for normality and homogeneity of variance.
2.1 Comparison of anatomical parameters of proximal femur between age groups of the same gender
Four groups of data were analyzed by one-way analysis of variance (ANOVA) and the least significant difference (LSD) test. P < 0.05 was considered statistically significant.
2.2 Correlation between anatomical parameters of proximal femur and age
Pearson correlation analysis was used. P < 0.05 was considered statistically significant.
2.3 Comparison of anatomical parameters of proximal femur between genders in the same age group
Independent samples t-test was used for intra-group comparison. P < 0.05 was considered statistically significant.
2.4 Comparison with previous studies
Summary independent samples t-test was used. P < 0.05 was considered statistically significant.