Specimens and femoral neck section anatomy:
33 dry, intact femoral specimens from 17 adults (13 men and 4 women; average age 58.5 years, range, 49 to 72y) were from donations by the Department of Anatomy, County Health School. Written consent was obtained from the people before death or from next of kin to use the specimens in this study. This study was approved by ‘the ethics committee of our hospital’. No visible deformity and no defects on distal and proximal femurs were observed.
One unpaired dry femoral specimen was cut perpendicular to the long axis of the femoral neck in the middle of the femoral neck to expose the femoral neck section. It can be seen that the cross section of the femoral neck is approximately ellipse formed by multiple curved surfaces, consisting of shorter upper and lower edges, longer anterior and posterior walls. The anterior wall is longer and less radian, so it can be seen as a surface, and it’s defined as the anterior surface. The posterior wall is semicircular and has a larger arc, which can be regarded as two surfaces with small arcs, and were defined as the posterosuperior surface and the posteroinferior surface separately (Fig.1A).
define the surface coronal angle
The angle between the three surfaces of the femoral neck wall and the coronal plane of the femur, which determined by the nadir of the greater trochanter and the medial and lateral condyles of the femur, was defined as each the surface coronal angle. For the convenience of description and measurement, the femoral neck section in the middle of the femoral neck was taken. The two ends of each surface are connected to form the chord of the surface. The angle formed by the chord and the coronal place of the femur is defined as the surface coronal angle. In this way, the femoral neck wall curved surface and femoral coronal plane respectively constitute three surface coronal angle: anterior surface coronal angle (ACA), posterosuperior surface coronal angle (PSCA) and posteroinferior surface coronal angle (PICA) (Fig. 1B).
parameters of femoral neck section and the surface coronal angles were measured
There were 32 dried femur specimens, 16 on each side. The circumference of the femoral neck section, the length of the upper and lower edges, the anterior surface, posterosuperior surfaces and the posteroinferior surface were measured with a tape measure. The dried femur is laid on the countertop which is in contact with the nadir of the greater trochanter and the medial and lateral condyles of the femur. A Kirschner wire was applied to attach each of the three surfaces of femoral neck wall, when the Kirschner wire reached the maximum contact with the corresponding surface, the Kirschner wire was fixed and the femoral specimen was removed. The angle between the Kirschner wire and the worktable was measured directly with a protractor, and the protractor reading is used as the data of corresponding surface coronal angle size.
model of femoral neck wall attached with steel wire wind aluminum foil
The aluminum foil paper (original thickness 10nm, folded thickness 1.28mm) was cut into the corresponding size of the anterior surface, posterosuperior surface and posteroinferior surface of the femoral neck wall, by closely attaching the surface, it is shaped into corresponding structure of each surface. Remove the aluminum foil paper and wind steel wire with a diameter of 0.5mm on its surface with a spacing of 2-3mm. Then attach it to the femoral neck wall with double-sided tape to make a steel wire wind aluminum foil model (Fig. 2A). The fluoroscopic image of the steel wire wind aluminum foil paper represents the image characteristics of the certain curved surface.
Multiangle radiography of steel wire wind aluminum foil model
Philips BV Endura X-ray machine (Netherlands), C-arm opening diameter 77cm, arc depth 61cm, maximum rotation angle 115°. The machine was placed on the projection position that the C-arm was perpendicular to the long axis of the femoral neck, and about 45° from the femoral shaft (adjusted according to the neck-shaft angle of femoral neck). With the midpoint of femoral neck as the center point of projection, it is defined as 0° position when the X-ray generator is away from the main machine, in contrast, when the generator is close to the main machine is 180° (Fig. 3).
Three pieces of steel wire wind aluminum foil paper were placed in turn and closely attached to the corresponding surface of the femoral neck. After fixing the femoral specimen on worktable, the projecting center line was adjusted, then rotating the C-shaped arm to take X-ray images of femoral neck. The C-arm was set to rotate at 5° intervals between 0° and 180°, and 37 fluoroscopic images were obtained from each steel wire wind aluminum foil model. When the image size of the steel wire wind aluminum foil is changed into the minimum, the angle between the worktable and the projecting center line is considered as the appropriate fluoroscopic angle of the corresponding curved surface of femoral neck, and its value is recorded. This image is also named as the tangent image of the certain curved surface.
model of three Kirschner wires perforating femoral neck wall
One femoral specimen that completed the aforementioned measurement experiment was taken. Three Kirschner wires with a diameter of 2.5/2.0/1.5mm were implanted from the femoral lateral wall through the femoral neck to the femoral head, and the three Kirschner wires pierced the anterior surface, posterosuperior surface and the posteroinferior surface, respectively. As thus, the model of three Kirschner wires piercing the femoral neck wall was completed (Fig. 2B). according to the above fluoroscopy method, the C-arm was rotated every 5° to complete the fluoroscopic angle range from 0° to 180°. The Kirschner wire penetrating the femoral neck wall on the image was observed. especially the five fluoroscopy angles as bellow: traditional posterior-anterior and lateral views, three appropriate fluoroscopic angles of the corresponding curved surface of femoral neck which obtained in the aforementioned experiment.
Statistical analysis
Continuous variables such as the circumference of the femoral neck section, the length of the upper and lower edges, the anterior surface, posterosuperior surfaces and the posteroinferior surface, the surface coronal angle (ACA, PSCA and PICA), the appropriate fluoroscopic angle, were expressed as mean and standard deviation (SD), then analyzed using the Student’s t test. The statistical analyses were done using Microsoft Excel. A value of P < 0.05 was considered as statistically significant.