It is of great therapeutic significance for the injured pelvis with poor stability and multiple complications represented by some Tile B and all Tile C pelvic fractures that how to achieve the effective fixation of the pelvic anterior and posterior rings through minimally invasive treatment, and how to quickly develop the best scheme of minimally invasive fixation according to the time, local conditions and injury conditions.
Progressive and retrograde percutaneous pubic intramedullary screw technique avoids extensive exposure during operation via ilioinguinal approach etc, and achieves ideal clinical results in the treatment of pelvic and acetabular fractures. However, because of the risk of bladder injury, iliac artery and vein injury and hip joint misentry, cannulated screw is a relatively safe choice. Even so, anatomically variant anterior pelvic rings (such as curvature of the superior ramus of pubis, diameter and shape abnormalities of the medullary cavity) often limit the placement of intramedullary screws. Although longer screw can provide better stability, the risk of screw breakage is significantly increased when the screw is too long (length > 100 mm) and too thin (diameter < 6.5 mm). Therefore, the diameter of superior pubic branch less than 6.5 mm is also a contraindication of intramedullary screw technique. Because the pubis is close to the bladder, iliac artery and iliac vein, retrograde screw placement based on the easily accessible pubic tubercle is safer. With navigation or robot assistance or not, compared with anterograde screw placement, it is more maneuverable and more suitable for one-stage anterior ring internal fixation under the guidance of ETC principle.
The conventional plate technique of anterior ring combined with posterior ring internal fixation has been used for the final internal fixation of unstable pelvic fracture. However, the technique is not suitable for the early treatment of pelvic injury because the open reduction and internal fixation for anterior ring injury is not minimally invasive. By contrast, anterior ring bridging long plate has the advantage of minimally invasive percutaneous implantation, which effectively avoids the pain of surgical site and incision complications, and significantly reduces the incidence of iatrogenic injury such as vascular and nervous system. It can be seen that anterior ring bridging long plate meets various requirements of first-stage treatment. Because of the low requirement for the anatomical shape of the anterior pelvic ring, the technique has wide indications and can be used as an effective supplement to the superior pubic intramedullary screw. However, due to the long plate and few screw, its biomechanical properties still need to be further studied.
As an ‘inbuilt external fixator’, the pelvic anterior screw-rod system creates the principle of fixation above the acetabulum in order to stabilize the anterior pelvic ring by minimal screw and more minimally invasive means, and to help fracture reduction by lateral compression and stretching. It is widely used in Tile B and Tile C pelvic injuries. The fixation is located in the body, does not affect sitting, standing and walking, and is suitable for obese patients especially for severe patients with abdominal organ injury. However, the screw placement requires higher technique, and there is a risk of iatrogenic injury of anterolateral femoral cutaneous nerve and hip joint capsule, with a higher incidence of heterotopic ossification, and internal fixation needs to be removed by a second operation. In addition, bilateral fixation is necessary for both unilateral and bilateral pubic branch fractures, so the biomechanical characteristics of this fixation and its possible impact on pubic symphysis deserve indepth study.
Thus, three kinds of pelvic anterior ring minimally invasive internal fixation methods have their own advantages and disadvantages. It is worth further study that how to choose an effective and safe fixation method to maximize the biomechanical advantages, avoid internal fixation failure and facilitate early functional exercise.
In this study, it was found that under the simulated bipedal standing state, there were no significant differences in the vertical, bilateral and anteroposterior stability of the fractures between the models of percutaneous superior pubic intramedullary screw, percutaneous bridging plate and percutaneous anterior ring screw-rod system and their combined fixation. Then, the author simulated the state of standing on single foot, and the results were similar to those of the state of standing on two feet. This suggests that the anterior pelvic ring contributes little to the overall vertical stability of the pelvis. Therefore, anterior-posterior loads and right-and-left loads were applied to the pelvis to simulate the mechanism of open-book and lateral damage. By comparing the displacement of the virtual acetabular midpoint in vertical, transverse and anteroposterior directions, the translation and rotation stability of three kinds of anterior ring fixation and their combined fixation on coronal, sagittal and horizontal planes was determined. The results show a significant unity. Comparing the multidirectional stability of three kinds of anterior ring internal fixators’ independent fixation, the percutaneous superior pubic intramedullary screw is the best, the percutaneous anterior ring screw-rod system is the second, and the percutaneous bridging plate is the worst, which shows the significant mechanical advantage of intramedullary centraxonial fixation. Although the fixation effect of anterior ring screw rod system is affected by indirect fixation across pubic symphysis, it still shows better mechanical characteristics than bridging plate with eccentric fixation. Considering the material consistency of the three internal fixators, it can not be excluded that this result may be related to the bridging plate’s ‘congenital deficiency’ of thin and flat plate and short screws far away from fracture site.
In order to maximize the effect of internal fixation, the author plan to combine three kinds of anterior ring minimally invasive internal fixation devices in pairs. However, the superior pubic intramedullary screw and bridging plate can not be fixed simultaneously because of the limitation of anterior ring anatomy, so only the anterior ring screw-rod system can be combined with the intramedullary screw and bridging plate respectively. The experiment show that, compared with the independent fixation modes, the combined anterior ring internal fixation modes show obvious mechanical advantages, among which the combination of the superior pubic intramedullary screw and anterior ring screw-rod system achieves the most stable fixation effect. Although the combination of bridging plate and anterior ring screw-rod system is superior to their independent fixation, it is still inferior to the single superior pubic intramedullary screw. This suggests that in the clinical practice of fixing bilateral pubic fracture, superior pubic intramedullary fixation should be preferred as far as possible. In order to minimize the failure risk of internal fixation, it is suggested to combine superior pubic intramedullary screw with anterior ring screw-rod system fixation. When there is no condition for intramedullary fixation, the combination of anterior ring screw-rod system with bilateral bridging long plate can be used as much as possible. If there is no condition for fixation combination, the anterior ring screw-rod system should be selected as much as possible to avoid the single fixation mode of bilateral long plates.