The purpose of our study was to investigate the value of the intra-operative tangential view to determine the posterosuperior femoral neck screw IOI in clinical applications. This study observed that the tangential view was more sensitive than the standard lateral view in distinguishing the posterosuperior screw IOI. Therefore, we recommend that the tangential view should be used as a routine C-arm machine fluoroscopic plane during the implantation of the cannulated screw guide wire for internal fixation of femoral neck fractures. When the tangential view reveals that the femoral neck screw guide wire is IOI or very close to the femoral neck cortex, the position of the guidewire should be promptly adjusted (Fig. 4 Tangential view instructs femoral neck screw guide wire implantation. A: intra-operative the lateral views showed the posterosuperior screw guide wire were contained within the femoral neck. B: intra-operative the tangential view showed the posterosuperior screw guide wire IOI. C: adjust the guidewire under the tangential view.).
Bony violation during screws fixation has been widely reported in the orthopaedic literature. Routt et al. suggested iliosacral screw insertion into the sacral isthmus region required avoidance of IOI to reduce the risk of damage to the adjacent neurovascular structures12. Du et al. recommended the C2 pedicle screw IOI to provide multicortical 3-column rigid fixation in the patients with basilar invagination and atlantoaxial dislocation13. Ramesh et al. proposed anterior column lag screw IOI in the fixation of acetabular fractures to provide rigid stability and minimize the surgical duration, radiation exposure, and intra-operative complications14. A previous clinical study demonstrated the posterosuperior screws IOI incidence up to 54% in the inverted triangle cannulated screws fixation of femoral neck fractures. However, the sensitivity of the standard lateral view to identifying the posterosuperior screw IOI was only 39%15. In a cadaveric study, 2 orthopaedic traumatologists and 1 musculoskeletal radiologist determined that no screws radiographically breached the posterior and cranial cortex in 10 cadaver specimens under the standard femoral neck AP and lateral views. After dissection, 70% of the specimens emerged with the posterosuperior screw IOI16. Aibinder et al. proposed the use of the sequential fluoroscopic rollover images to detect an IOI position after placement of the posterosuperior guide wire into the femoral neck17. However, this technique significantly increases the frequency of intraoperative fluoroscopy, leading to surgeons-possible damage by occupational ionizing radiation exposure18; 19. Therefore, this technique is not recommended for clinical applications. Adams et al. proposed placing the posterosuperior screw to the piriformis fossa inferior margin on AP view to avoid cortical breach during percutaneous screw fixation of femoral neck fractures9. However, we considered the screw location was a three-dimensional position so relying on the anatomical signatures on AP view alone was not credible, and our clinical cases validated the inaccuracy of this methodology (Fig. 3). In summary, no research was available to instruct guide wire implantation intraoperatively and thus avoid the femoral neck screw IOI.
However, the influence of IOI screws in the fixation of femoral neck fractures has not been clearly demonstrated. Femoral neck fractures frequently involve complications such as non-union and avascular necrosis, which are associated with disruption of the blood supply to the femoral head. 20Conventionally, the superior retinacular artery (SRA) derived from the medial femoral circumflex artery is considered to be the main blood supply to the femoral head21; 22. The SRA ran through the lateral retinaculum which had the form of a quadrilateral plate adjacent to the posterosuperior surface of the femoral neck23. The posterosuperior screw was “in-out-in” near the area where the superior retinacular artery enters the femoral neck, which means that there is a high risk of screw perforation invading the artery16. Due to the effects of the iatrogenic injury on the intraosseous vascular system, the blood supply of the femoral head is severely deteriorated, leading to non-union and secondary femoral head avascular necrosis24; 25. Yuan demonstrated that the incidence of avascular necrosis and revision surgery in hips with and without IOI screws was 6% and 6%, respectively; however, due to the width of the confidence intervals, a true clinical difference could not be excluded15. We believe this consequence was also related to the small sample volume. Thus, it is necessary to avoid the posterosuperior screw IOI in the internal fixation of femoral neck fractures.
The cross-sectional morphology of the femoral neck is displayed as a rotating forward ellipse26. With increasing osteoporosis, the trabeculae come to lie progressively more anterosuperior within the femoral neck, with a larger posterosuperior defect7. Therefore, the posterosuperior region is a risk area for bony violation during screw fixation of femoral neck fractures. This also explains that the screws appearing well contained in the standard view might have actually perforated the posterosuperior neck. It was worth mentioning that we found one patient with the inferior screw that was IOI in the postoperative CT (Fig. 5A, B: intra-operative the AP and lateral views showed all screws were contained. C: intra-operative the tangential view showed the inferior screw IOI. D, E: Postoperative plain radiographs showed all screws were contained. F, G: Postoperative CT showed the inferior screw IOI. The red arrow represents the inferior screw IOI.). Intraoperative standard AP and lateral fluoroscopy showed that the inferior screw was completely contained in the femoral neck, while the tangential view showed the inferior screw was IOI. This might be attributed to the inferior screw being implanted anteriorly and penetrated anteroinferior through the femoral neck, while the tangential fluoroscopy tangential to both the posterosuperior and anteroinferior cortices could reveal the accurate screw position.
In our clinical practice, we also concluded certain experiences to avoid IOI. Apply tangential view as a conventional fluoroscopic angle to adjust the guidewire. We usually implant the posterosuperior screw lower than the anterosuperior screw to avoid bony violation, thus creating an oblique triangle configuration27. Emphasize the importance of intraoperative manipulation of the senses. A sudden loss of resistance during the cannulated screw guidewire insertion, followed by a sudden reappearance of resistance, may suggest the guidewire IOI. When the femoral neck is narrow, such as in elderly women, we will replace the posterosuperior crew with a 6.5mm diameter screw to guarantee mechanical strength while reducing the risk of the posterosuperior femoral neck screw IOI.
However, there were some limitations to this study. This was a retrospective study and the number of cases was minor, which may be responsible for the high sensitivity of the tangential view to detect the posterosuperior femoral neck screw IOI. Therefore, a larger multicenter prospective study is necessary in the future to evaluate the sensitivity and sensitivity of the tangential view to detect the posterosuperior femoral neck screw IOI. Due to the different anatomy of the population, 150° tangential fluoroscopy may not apply to all patients. A large sample of femoral neck cross-sectional anatomical studies is necessary to obtain a more accurate tangential position projection angle. Intraoperative anatomical reduction is paramount, and non-anatomical reduction can also lead to the inaccuracy of the tangential view. This was only a radiographic comparison study, and the effect of IOI screws on the clinical prognosis of femoral neck fractures needs to be investigated subsequently.