| As we all know, with the development of diagnosis and treatment of thoraco-lumbar injuries, the integrity of spinal posterior ligament complex has been considered as an important basis for the options of the stability evaluation and treatment options in the thoracolumbar injuries severity score system. As a similarly complex and serious injury, pelvic fractures often have the joint injuries of bones and ligaments, but our knowledge on the mechanism of ligament injury in pelvic fracture is not complete. Currently, the diagnosis for pelvic ring injuries still stays on the level of X-ray and CT scanning, and the status of the ligaments can only be speculated from the translocation of the bone structures seen in the medical imaging results without direct observation, not to mention improving the overall diagnosis and treatment for pelvic fractures by the diagnosis of pelvic ligament injuries. The two major reasons for this situation are:1. the pelvic ligaments are more complicated, and the injury mechanism and the biomechanical studies are still not comprehensive or complete; and 2. the medical imaging findings and conclusions of ligament injuries are very difficult to achieve precisely.External rotation injuries of the pelvis (the APC type) are usually considered to be caused by the pelvic ligament injuries. But the signs and symptoms of the ligament injuries are still debatable, so are the treatment plans. Therefore, the next step should be biomechanical research and MRI to further evaluation the APC-type pelvic ligament injuries, and then the pelvic stability should be assessed considering the status of the bone and ligament injuries, so as to propose a better classification and treatment plan for n the APC-type pelvic injuries, to avoid the missed diagnosis and miscalculation for unstable pelvic injuries in clinical practices, hence to reduce the pain and to improve treatment success rate.Part I The Mechanism of Ligament Injuries in Young-Burgess APC II Pelvic InjuriesObjective:to determine the injuries and fractures of the sacrospinous ligament and the sacrotuberous ligament with the separation of symphysis pubis and the anterior sacroiliac ligament fracture, in APC II injuries, and the degrees of the separation of symphysis pubis, and the separation of the sacroiliac joint, so as to have a deeper understanding of the pelvic ligament and bone injuries.Methods:Complete pelvis specimens were separated from 10 unembalmed/fresh cadavers (female=3, male=7), with the complete section of L5 and complete preservation of pelvic ligaments. The specimens were divided into 2 groups randomly, and the test models were set up for two types of external rotation injuries of the pelvis: The group of fixed hemipelvis (the limited group), and the unfixed hemipelvis group (the unlimited group). Then the external rotation injuries of the pelvis, and the final data components were acquired from the biomechanical equipment which recorded the angle displacement under each torque. The biomechanical torque curve recorded a transition time point of the anterior sacroiliac ligament fracture, when all the anterior sacroiliac ligament of all specimens in this study presented fracture or severe distortion. At the transition point, the separation of the pubic symphysis, the anterior separation distance of the sacroiliac joint, the injuries and fractures of the sacrospinous ligament and the sacrotuberous ligament were recorded with visual observation, motion capture system and real-time video recording system. With the continuous external rotation of the hemipelvis, the sacrospinous ligament and the sacrotuberous ligament were gradually made to breakdown and fracture, then the bone changes and the injuries of posterior pelvic ligaments were observed and recorded.Results:as shown in the results of both limited and unlimited groups, with the failure of the anterior sacroiliac ligament, the average separation distance of the pubic symphysis was 23.8±2.8mm, the average anterior separation distance of the sacroiliac joint was 10.9±4.4mm. Paired t test was conducted to compare the separation distance of the pubic symphysis and the anterior separation distance of the sacroiliac joint during the t anterior sacroiliac ligament fractures between the two groups, and the differences were not statistically significant (P>0.05). During the anterior sacroiliac ligament fractures, the average external rotation angle of both groups was 40.1±9.8°, and the average torsion was 646.7±131.5N. Paired t test was applied to compare the external rotation angles and torsions during the anterior sacroiliac ligament fractures between the two groups, and the differences were statistically significant (P<0.05) with bigger external rotation angles and torsions in the unlimited group. In the unlimited group, during the anterior sacroiliac ligament fractures, there were no obvious injuries or fractures found in the sacrospinous ligament or the sacrotuberous ligament. However, in the limited group, there was 1 case of the sacrotuberous ligament fracture (20%), and 3 cases of the sacrospinous ligament fractures (60%). After the factures of the anterior sacroiliac ligament, the external rotation wasn’t stopped. With the extreme external rotation, there were still no obvious injuries or fractures found in the sacrospinous ligament or the sacrotuberous ligament in the unlimited group, but there were the injuries of the interosseous sacroiliac ligament and the posterior sacroiliac ligament, the rotational displacement of the sacroiliac joint. While with continuous rotation of the limited group, there were fractures of the sacrospinous ligament and the sacrotuberous ligament, with the sacrospinous ligament fractures before the sacrotuberous ligament fractures. When both ligaments were fractured, the interosseous sacroiliac ligaments were all injured. But the hemipelvis was fixed; therefore there were no injuries of the posterior sacroiliac ligament. In the limited group, when the anterior sacroiliac ligament, the sacrospinous ligament and the sacrotuberous ligament were all fractured, the average distance of the pubic symphysis separation was 41.8±7.7mm, and the average distance of the anterior separation of the sacroiliac joint was 16.8±4.0mm.Conclusion:In this study, we had the following several major findings. Firstly, there could be two types of situations of external rotation injuries of the pelvis, i.e. the limited and the unlimited hemipelvis, which could have different external rotation injuries of the ligaments. Bigger rotation angles and torsions were needed for the fractures of the anterior sacroiliac ligament in the unlimited group. Also, during the fractures of the anterior sacroiliac ligament, there were no obvious injuries or fractures of the sacrospinous ligament or the sacrotuberous ligament, while there were injuries in all specimens of the limited group. Secondly, the results of this study found that the average pubic symphysis separation distance during the breakdown of the anterior sacroiliac ligament was 2.4cm. During the breakdown of the anterior sacroiliac ligament, there could still be considerate fluctuations of the pubic symphysis separation distance. Thirdly, during the injuries of the anterior sacroiliac ligament, there were not necessarily the injuries of the pelvic ligaments (i.e the sacrospinous ligament and the sacrotuberous ligament). Only 10% of all the specimens (1/10) presented complete fractures of the sacrospinous ligament and the sacrotuberous ligament, while there were no fractures of the sacrospinous ligament or the sacrotuberous ligament in the specimens of the unlimited group.Part II:MRI Visualization of Related Ligaments of Anteroposterior Compression Pelvic InjuriesObjective:to investigate whether MRI can detect the existences of the anterior sacroiliac ligament, the sacrotuberous ligament and the sacrospinous ligament inside the pelvic ring. Based on the studies of the ligament scanning of other body parts, the best scanning sequence and angle for the visualization of the three ligament groups was determined, so as to provide some basis to the next-step determination of ligament injuries in the cases of pelvic fractures.Methods:30 healthy young adults were selected (female=10, male=20, age=20-40 years old) in this study. With Signa HDxt 3.0T Magnetic Resonance Imaging System (GE, USA), the axial scanning sequences of T1WI, T2WI, PDWI and 3D-FIESTA were conducted, the Carrier to Noise Ratio (CNR) of the lipid and the tendons were calculated, and the anterior sacroiliac ligament, the sacrotuberous ligament and the sacrospinous ligament were searched in the axial scanning images. According to the results of the CNR values of the lipid and the tendons in the transverse axial scanning sequences and the directions of the ligaments, the oblique sagittal and the oblique coronal scanning sequences of TIWI and 3D-FIESTA were performed for the sacrotuberous ligament and the sacrospinous ligament. The oblique axial and coronal scanning sequences of TIWI and 3D-FIESTA were performed for the anterior sacroiliac ligament. The oblique scanning of the ligaments was based on the 3D location:in the oblique coronal scanning, the starting points or the bone landmarks of the sacrotuberous ligament, the sacrospinous ligament and the anterior sacroiliac ligament were found on the axial and the coronal positions, and the scanning were performed on the coronal sections with the connections of the point-point lines of the bone landmarks. The imaging results were saved in the Picture Achieving and Communication System (PACS) of the Second Affiliated Hospital of Wenzhou Medical University, and was read by 2 experienced attending physicians familiar with the regional anatomy of the pelvis, with consensus achieved by discussions in case of any different readings. And the signal intensities of the lipid and the tendons in the images of all axial scanning sequences including TIWI, T2WI, PDWI and 3D-FIESTA were measured, and the standard deviation of the background signal intensity was calculated. Then the CNR values of the lipid and the tendons in the images of all scanning sequences were compared with the results of the 3D-FIESTA sequence. Then the display effects of the anterior sacroiliac ligament, the sacrotuberous ligament and the sacrospinous ligament in the images of the axial and oblique scanning sequences of 3D-FIESTA and Tlwl were observed, with identification and scaling for each layer, and then the data was analyzed statistically.Results:after paired t test, there was no statistical significance of the CNR values of the lipid and the tendons between the images of scanning sequences of 3D-FIESTA and TIWI, while the results of 3D-FIESTA sequence was significantly higher than the values of PDWI and T2WI sequences. The axial and oblique axial scanning could basically present clearly the full length of the anterior sacroiliac ligament; and the coronal scanning could only show the full length of the anterior sacroiliac ligament in 16 cases, while the sagittal scanning couldn’t show the anterior sacroiliac ligament. With the calculation of Wilcoxon signed-rank test, the oblique sagittal scanning of the sacrotuberous ligament presented the best images with clear identification of the full length, broad ligament shape and many layers. Also, the oblique coronal scanning of the sacrotuberous ligament could also display the full length, thin ligament shape and few layers. While the axial scanning of the sacrospinous ligament could basically show the shape of the ligament, but with difficulties for the full length, the oblique sagittal scanning of the sacrospinous ligament could show the full length with thin ligament shape and uneven signals, which was not as clear as the image of the sacrotuberous ligament. The sacrospinous ligament was hardly recognized in the coronal scanning. With 2D reconstruction of the images of the sacrospinous ligament and the sacrotuberous ligament with 3D-FIESTA sequence, the results could show more complete shapes of the ligaments.Conclusion:1. The CNR values of the lipid and the tendons were highest in the TIWI and 3D-FIESTA sequences, and this indicates that TIWI and 3D-FIESTA sequences can clearly display the normal pelvic ligaments.2. The images of the anterior sacroiliac ligament were the clearest in the axial scanning, while not as good in the oblique axial scanning or coronal scanning, and couldn’t be identified in the sagittal scanning.3. The axial scanning images mainly showed the sections of the starting and the ending points of the sacrospinous ligament and the sacrotuberous ligament. The oblique sagittal scanning of the sacrotuberous ligament presented the best images with clear identification of the full length, broad ligament shape and many layers. Also, the oblique coronal scanning of the sacrotuberous ligament could also display the full length, thin ligament shape and few layers.4. Because of the oriental direction, the display of the sacrospinous ligament was quite thin. On the side of the sacrum, the sacrospinous ligament and the sacrotuberous ligament overlap with each other a lot, therefore the ligaments could be displayed in the axial scanning while the full length was difficult to observe. Also, the oblique sagittal scanning could basically show the full length of the sacrospinous ligament with thin shape and uneven signals (less low signals), not as clear as the result of the sacrotuberous ligament. The sacrospinous ligament was hardly recognized in the coronal scanning. 5. The oblique scanning was performed based on the directions of the ligaments. The method was based on the 3D location by identifying the starting points or the bone landmarks in the axial, coronal or sagittal scanning, then the oblique scanning was performed with good results without prior selection of the scanning angle.6. While T1WI and 3D-FIESTA sequences could both clearly display the pelvic ligaments, the 3D-FIESTA sequence was applicable for 2D reconstruction of different locations; and the 2D reconstruction of the ligaments with angle differences could better display the ligaments.Part Ⅲ Preliminary Study on the MRI of Ligaments in Patients with Anteroposterior Compression Pelvic InjuriesObjective:to investigate the MRI results of ligaments in patients with external rotation injuries of pelvis, so as to find out whether the anterior sacroiliac ligaments, the sacrospinous ligament and the sacrotuberous ligament can be visualized in patients with external rotation injuries of pelvis, and to learn the real efficiency of MRI in ligaments of external rotation injuries of pelvis.Methods:6 patients with external rotation fractures of pelvis admitted and treated in the Second Affiliated Hospital of Wenzhou Medical University from Jan 1,2014 to Jan 31,2016. The patients of>18 years old with stable hemodynamic status and tolerable to receive MRI tests were included. According to the results of Part Ⅱ on the scanning methods, mainly the axial scanning and oblique sagittal scanning were performed with the sequences of T1 WI, T2WI, PDWI and 3D-FIESTA.Results:The MRI results of all the 6 cases could show the anterior sacroiliac ligament, the sacrotuberous ligament and the sacrospinous ligament. According to the classification of the pelvic compression injuries and the ligament injuries presented in the MRI results, and the measurement of the X-ray of the pelvis, there were 5 cases of APCII injuries and 1 case of APCI injuries of all the 6 cases, with no obvious fractures in APCI injuries. While in the cases of APCII injuries, the anterior sacroiliac ligaments were all fractured,2 cases presented obvious injuries of the sacrospinous ligament and the sacrotuberous ligament,2 cases had no obvious injuries or fractures of the sacrospinous ligament or the sacrotuberous ligament, and 1 case had the sacrospinous ligament injuries but no injuries of the sacrotuberous ligament. Also, we found that the separation distances of the pubic symphysis were not consistent with the ligament fractures. In Case 1, the separation distance of the pubic symphysis was 31.2mm, while there was no injury of the sacrospinous ligament or the sacrotuberous ligament; in Case 2, the separation distance of the pubic symphysis was 27.3mm, but there were obvious injuries of the sacrospinous ligament and the sacrotuberous ligament.Conclusion:1. All the MRI results could show the anterior sacroiliac ligament, the sacrotuberous ligament and the sacrospinous ligament in the cases of external rotation injuries of the pelvis. The axial scanning could show the full length of the anterior sacroiliac ligament with easy identification of the injuries. The axial scanning could also show the sections of the sacrospinous ligament and the sacrotuberous ligament, while the identification of the injuries was basically shown without the full length, which could easily lead to the misdiagnosis, and huge difficulties to confirm the diagnosis. The oblique sagittal scanning could clearly show the full length of the sacrotuberous ligament with easy identification of the injuries. The oblique sagittal scanning could also present part of the sacrospinous ligament with basic identification. 2. According to the classification of the pelvic compression injuries and the ligament injuries presented in the MRI results, in the cases of APCII injuries, the anterior sacroiliac ligaments were all fractured, unnecessarily combined with the fractures of the pelvic ligaments, i.e. the sacrospinous ligament and the sacrotuberous ligament; and this result was consistent with the results in the Part I biomechanical study. Also, the separation distances of the pubic symphysis were not consistent with the degrees of ligament injuries:patients with big pubic symphysis separation may have complete sacrospinous ligament and the sacrotuberous ligament, while patients with small pubic symphysis separation may have fractures of the sacrospinous ligament and the sacrotuberous ligament.3. The results of direct display of pelvic ligament injuries by MRI scanning may be different from the traditional determination of ligament injuries. Therefore, further studies are required to investigate the mechanism, diagnosis and treatment of external rotation injuries of the pelvis. |
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