The use of three cannulated screws in the treatment of femoral neck fracture has long been a routine technique for the surgical treatment of femoral neck fracture due to its simple and minimally invasive method, less bleeding and accurate curative effect [13–15]. However, due to the long clinical application time and the large number of patients receiving cannulated screw fixation, clinicians have found many problems in practice. Many studies focused on the analysis of the failure of cannulated screw fixation to improve the technique of cannulated screw fixation for femoral neck fracture [16–20]. A large number of relevant studies not only improve the success rate of cannulated screw fixation, but also standardize the fixation method and shorten the learning curve, so that the method of cannulated screw fixation is more widely used. During the operation, the c-arm can be used to simply understand the position of the screw, facilitate the insertion of the screw and avoid the cannulated screw cutout the femoral neck. Therefore, the cutout of cannulated screw has not been frequently researched and noticed, but can c-arm fluoroscopy effectively avoid the screw cutout? This study aims to review this issue and try to improve the existing intraoperative fluoroscopy techniques.
Studies have shown that sufficient screw length to reach the subchondral bone can improve fixation strength and reduce the possibility of fixation failure[6]. Especially the femur under the femoral head type fracture, if the thread can not cross the fracture line, often can not achieve follow-up pressure, leading to fixation failure. The screw is long enough to be close to the subchondral bone so that to increase the fixation strength, but it also increases the risk of the cancellous screw cutting out the femoral head. Once the screw is cutout and inserted into the acetabulum it may cause damage to the joint, leading to severe traumatic arthritis and even necrosis of the femoral head. Therefore, how to accurately grasp the length of the screw is the key to the success of cannulated screw fixation. Traction bed assisted reduction of femoral neck fracture is a most commonly used reduction technique in surgery. This method can not only simply and effectively reduce the femoral neck, but also achieve relative stability and avoid loss of reduction during fixation. At the same time, the use of traction bed can provide convenience for intraoperative C-arm fluoroscopy(Figure 2a,2b).
But the positive and lateral position of the femoral neck be shown in the c-arm during the operation can accurately display the length of the screw accurately and prevent the screw from cutting out the femoral head? According to the results of the retrospective analysis, 72 of the 479 patients with femoral neck fracture fixation with cannulated screws underwent postoperative CT examination, of which 18 cases had screw cutout, with a cutout rate as high as 25%. 11 cases were cutout from the position of the femoral head, and 9 of them were cutout from the anterior upper part of the femoral head. It can be seen that the anterior upper part of the femoral head is a high-risk area for screw cutout.
Through autopsy study, we found that when c-arm fluoroscopy was used during the operation, the screws cutout from the anterior upper and posterior upper part were easily covered by the maximum circumference of the femoral head due to the special fluoroscopy position(Figure 2c, 2d, 2e, 2f). Because the screw requires parallel femoral neck inserting, the femoral neck has a forward Angle, and the inverted triangle screw placement technology is widely used [22], the odd of femoral head cutout from the anterior upper is the biggest. These causes make the anterior upper part of the femoral head a high-risk area for screw cutout. If intraoperative CT data can be obtained, the screw cutout can be effectively avoided, but this is not possible in most medical institutions and it also increases the cost of treatment and increases the risk of radiation. Therefore, to solve this problem, we adopted intraoperative frog lateral view to verify whether the screw was cutout from the anterior upper༈Figure 3a༉. Through the test, when the affected hip is in the frog lateral view, the hip joint is extremely extended and rotated, so that the anterior upper area is parallel to the direction of the rays, and any cutout part will not be covered༈Figure 3b, 3c༉. In this study, none of the 41 patients who underwent intraoperative frog lateral view verification had the anterior upper screw cutout. It can successfully reduce the risk of cutout, lower the cost of treatment and avoid excessive fluoroscopy.
If intraoperative frog lateral view is not performed, even in the positive and lateral position of the femoral neck after the conventional fluoroscopy, the screw cutout cannot be effectively detected. First of all, after out of the state of anesthesia, the patient can not cooperate with the lateral perspective fluoroscopy mostly because of pain. Secondly, even if some patients are able to cooperate, they could not fully abduct and rotate the hip joint as fully as the frog lateral view during the operation. The upper anterior cutout is still easy to be covered by the maximum circumferential diameter, which is also the main reason why the positive lateral X-ray cannot effectively prompt the incision in this study. In addition, intraoperative frog lateral view examination before the patient leaves the traction bed more conducive to correct screw cutout. If the patient leaves the traction bed, even if the screw is found to cutout the femoral head after the frog position examination, it is difficult to find the position of the screw from the original skin incision due to the change of the traction position. Usually need to increase the incision and adjust, but this will increase the trauma and prolong the operation time. During the operation, the frog lateral view fluoroscopy examination was performed on the traction bed. If the screw is cutout, the lower limbs are directly restored to the previous position for traction, and the screw cap can be easily found through the previous skin incision, avoiding the expansion of the incision.
At present, there are some research problems shown in this paper as follows:
1. In this study, although the use of the frog lateral view can reduce the risk of screw cutting out of the anterior and upper femoral head area, the screw still has a low probability of cutting out from other positions, so cutting out cannot be completely avoided; 2. In this study, the prognosis and outcome of patients with screw cutout were not further followed up. The consequences of screw cutout at different locations should be further studied; 3. More precisely designed experimental studies, larger sample sizes and long-term follow-up are needed to verify this point.