After internal fixation of femoral neck fracture, traumatic necrosis of the femoral head is still a major complication. How to reduce the rate of necrosis is a major problem in Orthopaedic Trauma[17, 18]. The blood supply of the femoral head is mainly from the medial and lateral femoral circumflex artery. The fracture is usually accompanied by the distortion, deformation and obstruction of the blood vessels in the femoral neck region. At the same time, the pressure increase in the joint capsule after the fracture which further reduces the blood supply to the femoral head, avascular necrosis of the femoral head occurs when residual blood supply is not compensated [19,20]. Therefore, the quality of the reduction of the femoral neck fracture is related to the blood supply of the femoral head. The anatomical reduction of the femoral neck fracture can provide the best environment for the revascularization of the femoral head [21]. How to improve the quality of fracture reduction during surgery is particularly important [5].
The garden index was first proposed by Garden [9] in 1964 and is still the classic standard for clinical reduction of femoral neck fractures. The specific content is: In the antero-posterior radiograph these the fan-shaped medial group of trabeculae in the head of the femur normally lie in alignment with their projections in the adjacent pelvis, and a line drawn through the long axis of the group forms an angle of approximately 160 degrees with the medial cortex of the femoral shaft. In the lateral view the central axis of the head and the central axis of the neck lie in the same straight line. The normal antero-posterior/lateral relationship of the two fragments can thus be expressed as an alignment index of 160/180. At the same time, Garden [4] also pointed out that regardless of the anterior-posterior or lateral position, the femoral head necrosis rate of the garden index between 155 ° and 180 ° is 6.6% (16/242), less than 155 °, or more than 180 °, will greatly increase the incidence of femoral head necrosis, from 65.5% (53/81) to 100% (26/26). As a classic rule for evaluating the reduction quality of femoral neck fractures, the garden index is still adopted by most orthopaedic surgeons.
However, the Garden Index is a measurement based on a two-dimensional plane, and it does not make explicit provisions for rotatory displacement of the femoral neck in three-dimensional space. Therefore, we used imaging studies of cadaver specimens to determine whether the garden index can determine the rotatory displacement of femoral neck fractures. We found that within the range of pronation 30 ° or supination 30 °, the garden index did not change significantly, and there was no statistical difference. Therefore, we believe that the rotatory displacement of femoral neck fractures within 30 °, the garden index cannot be accurately judged. The rotatory displacement from 40 ° to 90 ° shows a significant change in the garden index no matter whether it is pronation or supination. According to our analysis, X-ray is a two-dimensional planar image, but the femoral neck rotatory displacement in three-dimensional space cannot be accurately judged, Only when the rotatory angle increases to a certain degree and there is obvious misalignment, the garden index will change to some extent. This also prompts us to use the garden index to evaluate the reduction quality is not completely reliable. We need more accurate instruments such as intraoperative 3D CT to more accurately display the reduction quality of femoral neck fractures.
We have also found some imaging markers in repeated research, in order to assist in determining the rotatory displacement of femoral neck fractures during surgery. We initially found that during the proximal rotation of the femoral neck fracture, the fovea area of femoral head on the anterior-posterior view showed a certain change law, which can help judge the rotation of the femoral neck fracture during the operation. The fovea of femoral head is located at the center of the femoral head and connects the round ligament. With the rotation of the femoral head, the fovea of femoral head appears on the two-dimensional image of the X-ray, showing an increase or decrease in area. In the process of femoral neck fracture reduction, it can be used to help judge the change of rotation.
However, how many degrees of rotatory displacement will affect the blood supply of the femoral head and then cause necrosis of the femoral head? There are currently no relevant literature reports. We will use animal experiments and clinical case follow-up studies for further verification in future studies.