| BackgroundWith the development of social economy and the quickening pace of life, the incidence of acetabular fratures which caused by high-energy injury also increases. Except simple anterior and posterior wall fractures, the quadrilateral plate may be involved in other types of acetabular fractures. Due to the powerful violent force, fractures of the quadrilateral area are mostly comminuted and usually accompanied by fragments shifted to the pelvic cavity, central dislocation of the hip joint can be caused in severe cases. At present, most of the orthopedic surgeons advocate restoring the matching relationship between femoral head and acetabulum by open reduction and internal fixation, so as to effectively promote the recovery of function of the hip joint for patients after surgery. However, because of the extremely irregular anatomy and deep location of the acetabulum, which is surrounded by many important blood vessels and nerves, the bones in the quadrilateral area are weak and adjacent to the femoral head, thus placing internal fixation in this area is difficult, even the slightest mistake may cause serious complications such as screw penetration into the hip joint, while the strength may be greatly weakened if the internal fixation is placed away from the fracture line. Therefore, the treatment of acetabular fractures involving the quadrilateral area has been bothering the orthopedic doctors.The clinical treatment of the acetabular fractures involving the quadrilateral plate with a simple, direct, safe and effective internal fixation through a single approach has always been the goal of orthopedics doctors. In recent years, Professor Cai Xianhua and others of our department create the DAPSQ internal fixation system (Dynamic Anterior Plate-screw System for Quadrilateral area) and apply it to the treatment of acetabular fractures involving the quadrilateral area through a single ilioinguinal approach, in which the plate is placed along the "leading edge of sacroiliac joint-arcuate line of pelvis-superior ramus of pubis-pubic symphysis", due to the unique method of multiple elastic fixation on the surface of quadrilateral area, the system is quite safe, solid and reliable without the risk of screws penetrating into the hip joint. The postoperative follow-up of patients shows satisfactory curative effect. WuYongde etc. has conducted the relative studies of biomechanical stability in respect of the treatment of acetabular fractures by using DAPSQ. The experimental results shows that DAPSQ has a better biomechanical stability compared with other internal fixation systems. But in the course of clinical application of DAPSQ in the treatment of different types of acetabular fractures involving the quadrilateral area, we still had some problems to solve:How to select a reasonable position for plate placement and screws insertion according to the type of fracture combined with the anatomical features of bone? How to determine the reasonable diameter, length, direction of screws in different area? Therefore, to conduct relative applied anatomy study of this internal fixation system may contribute to the improvement of this technology, and will lay foundation for further popularization and industrialization of this technology. For this reason, on the basis of summarizing the experience of previous researches, we collected the complete pelvic CT scan images of adults in our hospital, and established three-dimensional models of the pelvises with the aid of digital medical software to study the anatomy of the acetabulum and its surrounding bones. In this study, according to screw placement characteristic of the DAPSQ, we chose the projections of the vertex of the greater sciatic notch and the obturator trailing edge on arcuate line of pelvis as the reference marks, and divided the semi-pelvis into the quadrilateral region, the iliac region and the pubic region. And then precise marking, measurement and statistical analysis of bone distribution characteristic in each region were performed, so as to find the anatomical landmarks and clear the weak areas, especially the area for quadrilateral-screws’placement, and finally to provide a theoretical reference for choosing the reasonable position and method for screw inserting in order to facilitate the fixation effective of DAPSQ in clinical application.Part oneStudy on the safety zone for screw insertion in the quadrilateral plate of the acetabulum via ilioinguinal approachObjectiveDigital measurement and statistical analysis are conducted to figure out the characteristic of osteal anatomy and confirm the safety zone for screw insertion in the quadrilateral plate of the acetabulum, so as to provide anatomical reference for safely and effectively screw insertion in this area.MethodsPelvic CT scan data were collected from 27 adults undergoing CT scan in our hospital from January to June,2015.The subjects consisted of 13males and 14 females and were 54.9 years old on average. The 3D pelvic model was reconstructed from the raw data using Mimics 10.01 and Geomagic Studio 12.0.The acetabular model was extracted, shelled, and recombined into the pelvic model. According to the distribution of bone thickness, the quadrilateral plate was divided into absolutely dangerous zone (<5mm), relatively dangerous zone (5～8.5mm), and safe zone (> 8.5mm) for screw placement. The distance from the special points (B and P) on the boundary of dangerous zones (absolutely dangerous zone and relatively dangerous zone) to the arcuate line of pelvis (ALP) and obturator foramen (OF) were measured and recorded as B-ALP, B-OF, P-ALP, and P-OF, respectively.And the distribution range (parallel and perpendicular to the pelvic brim) of dangerous zones were measured and recorded as BT, and PA, respectively. All results were converted to the relative width (w) and depth (d) of the quadrilateral plate. Comparison of the above indexes was made between the left and right sides of the pelvis as well as between males and females.ResultsThere were no significant differences in the above indexes between the left and right sides of the pelvis (P> 0.05).With the reference of the distribution map of the safety zone for screw insertion and the related data analysis results, the dangerous zones of screw placement (absolutely dangerous zone and relatively dangerous zone) was located at the anterosuperior portion of the quadrilateral plate and its scope ranged (i.e. the boundary of relatively dangerous zone) in the front 1/2 (0.52) or upper 1/2 (0.45) of the quadrilateral plate, thereinto the absolutely dangerous zone, which was approximately concentric circle like structure with the relatively dangerous zone, distributed in the center and ranged 1/3(0.27),1/4(0.24) of the width and depth of the quadrilateral plate, respectively. And the relatively dangerous zone was located around the absolutely dangerous zone. The safe zone ranged in the rear 1/2 (0.48) or lower 1/2 (0.55) of the quadrilateral plate, and located at the area (39.75±4.53) mm below the arcuate line of pelvic or (34.79±4.47) mm away from the obturator foramen. There were significant differences in the above indexes between male and female (P<0.05).ConclusionsThe distribution of bone thickness in the quadrilateral plate is characterized by "thick-thin-thickest" from top to bottom or from anterior to posterior. When dealing with fractures involving the quadrilateral area via ilioinguinal approach by laying the plate along arcuate line of pelvis, we should choose the appropriate way of screw insertion according to the distribution of the safety zone. Screws can be completely inserted into the bone by the direction of parallel to the surface of quadrilateral plate in the safe zone. The so-called quadrilateral screws can be used in the dangerous zone, among which, screws can be partially inserted into bone in the relatively dangerous zone, and should be placed entirely on the surface of bone in the absolutely dangerous zone, so as to realize the effective fixation for the fractures involving the quadrilateral area. Moreover that will be beneficial to improve the operation safety and shorten the operation time.Part twoStudy on the distribution of bone thickness in the iliac region and the digital measurements for safely screw insertion in the pubic regionObjectiveDigital measurement and statistical analysis are conducted to figure out the characteristic of osteal anatomy in the iliac region and confirm the safety way for screw insertion in the pubic region via ilioinguinal approach by digital measurement and statistical analysis, so as to provide anatomical reference for safely and effectively insertion of the so-called fixed screws in this area.Methods1. Measurement of the distribution of bone thickness in iliac regionPelvic CT scan data were collected and the 3D pelvic model was reconstructed from the raw data using Mimics 10.01 and Geomagic Studio 12.0. The external surface model of ilium was extracted, thickened (shelled for 5mm,10mm,15mm, 20mm respectively) and recombined into the pelvic model. According to the distribution of thickness, the iliac region was divided into 5 parts(less than 5mm, 5～10mm,10～15mm,15～20mm, and more than 20mm). Two lines that perpendicular and tangent to the sacroiliac joint was drew through the projection of the Iliosciatic Notch on the arcuate line (point IN). The distribution range along direction of the perpendicular line and the tangent line of the less than 5mm,5～10mm thickness areas were measured and recorded as RSJ, RIN.The minimum distances between the areas less than 5mm,5～10mm thickness and the perpendicular line, the tangent line, the Crista Iliaca were measured and recorded as DSJ, DIN, and DCI, respectively. The minimum distances between the forepart of 10～15mm,15～20mm thickness areas and the arcuate line of pelvis were measured and recorded as DALP, the minimum distances between this two areas and point IN were measured and recorded as DIN-min.2. Anatomic measurements for safely screws inserting in the pubic regionThe pubic region was divided into the obturator region and the symphysis pubis region referencing to the leading edge of the obturator by observing the changes of bone height. Series sections of the pubis were made using Mimics software at the leading and trailing edge of the obturator, the pubic tubercle and the synchondroses pubis. The points 5mm away from the arcuate line of pelvis on the anterior column surface were selected as the entrancepoint and 3.5mm diameter screws were simulated to insert into the bone at each section. Adjusting of the position, direction and length of screws in the "transparent" mode was conducted. The maximum length of the screws that can be inserted in each section and the angle between each screw and the inner side of the pelvis were measured and recorded.Results1. The distribution of bone thickness in the iliac regionFrom the anterior to posterior, top to bottom, the general thickness distribution characteristic of the ilium bones in the inner side of pelvis took the form of thicker, thin and thickest, among which, the area of less than 5mm thickness was located in posterior and top of the iliac, where there was the iliac fossa. Beyond that was the 5～10mm area, distributing roughly like concentric circles structure with the area of less than 5mm.The 10-15mm area had the widest range of distribution, with its margin extending along with the crista iliaca, front to the anterior inferior iliac spine, posterior to the iliac tuberosity and tangent to the sacroiliac joint. The 15-20mm area was mainly located above the greater sciatic notch, spreading like an inverted "S" and distributing between the leading of sacroiliac joint and the anterior superior iliac spine. The area of more than 20mm was located below the 15～20 mm area and in front of the leading edge of the projection of the acetabular on the anterior column.2. Anatomic measurement results of safely screw insertion in the pubic regionThe length range of screws that could be inserted in the obturator region was (18.03±1.65) mm to (40.31±4.87) mm for males, and (16.83±1.68) mm to (32.65±3.50) mm for females. The angle between screws and the inner surface of pelvis were (7.77±3.15) degrees outward, (4.66±2.27) degrees inward to pelvic cavity at the trailing and leading edge of the obturator for males, respectively. For females, it were (8.67±1.63) degrees towards the outside of the pelvis, (4.42±1.99) degrees towards the pelvic cavity. In the symphysis pubis region, the maximum length of screws that could be inserted at the pubic tubercle were (64.78±6.75) mm for males, (52.24±3.77) mm for females, and the entry angle were (5.03±1.93) degrees for males, (5.97±1.63) degrees for females when taking the inner surface of pelvis as the reference plane, and the direction of screws were towards the pelvic cavity. The maximum length of screws that can be inserted in the synchondroses pubis were (43.38±3.49) mm for males, (40.41±2.77) mm for females, and the entry angle were (3.98±2.75) degrees for males, (4.61±2.26) degrees for females when taking the inner surface of pelvis as the reference plane, and the direction of screws were towards the pelvic cavity. There were significant differences in the length of screws between male and female (P<0.01), while there were no significant differences in the angle of screws between male and female (P>0.05).ConclusionReasonable shaping and placing methods of the plate should be designed according to the fracture site and extending direction of the fracture line in the treatment of acetabular fractures involving the quadrilateral plate using DAPSQ. When inserting internal fixations in the iliac region, we should choose thick areas to insert screws basing on the thickness distribution of the ilium bones, so as to achieve a better fixation effect. When drilling and implanting screws in the pubic region, we should choose the right depth and direction in accordance with the position of entrance point:In the obturator region, the length of screws should be limited to less than 15～30mm, and especially in the trailing edge, it should not be longer than 20mm in order to avoid screws penetrating the superior ramus of pubis and causing damage to the important blood vessels and nerves in the obturator. Regarding the inner surface of pelvis as reference, the angle and direction of screws inserted at the trailing and leading edge of the obturator were about 8 degrees deviating from the pelvic cavity,5 degrees towards the pelvic cavity. When inserting screws in the symphysis pubis region, the length of screws should be not more than 50mm at the pubic tubercle, and less than 40mm near the pubic symphysis articular surface. Angles of screws were about 5 degrees towards the pelvic cavity on average. |
