ABSTRACT
Objective To investigate the entry point, direction and fixation range of Magic screw for acetabular posterior column fracture. Methods The 3D models of 100 pelvis were reconstructed by Mimics 19. 0 software based on CT data, and the virtual magic screw were placed in acetabular posterior column, then the screw' s entry point were determined, and the direction, length, diameter and safe range were measured respectively. Acetabular posterior column with magic screw was osteotomy modeling by Mimics 19.0 and imported the Geomagic Wrap 2017 software, after that anatomical parameters of the screw path were measured. Results The entry point of Magic screw on bone surface was located at (33. 37±5. 53) mm of the anterior inferior iliac spine moving posteriorly, and ( 13. 40±3. 70) mm of the apex of the upper margin of acetabular moving celphalad in male, which were (33. 97±5. 46) mm and (9. 01±3. 86)mm in female. The posterior inclination angle, interior inclination angle of magic screw and the angle between screw and iliac wing were (57.40±6.57)°, (52. 09±5. 65)° and (15. 21 ±3.42)° in male, which were (55. 64±8. 01)°, ( 51. 55±5. 58)° and (9. 85±3. 68)°in female. The maximum diameter of male screw was (6. 97±0. 98) mm, which was (6. 39±0. 85) mm in female. The length of male screw was (76. 73±9. 20) mm, which was (63. 64±8. 37) mm in female. The safe range of posterior inclination and interior inclination of were ( 7. 19 ± 3. 30)° and (9. 41 ±3. 95)° in male screw with 5.5 mm diameter, which were (8. 37±2. 82)° and ( 10. 32±3. 93)° in female screw with 5. 2 mm diameter. In the direction of the screw, the length range of the posterior column which is fixed by screw was (56. 87±7. 60) mm, and the proportion of fractures fixed with screws which were located on the top of the acetabular was 20/50 in male, which were (41. 71±7. 97) mm and 8/50 in female. Conclusion Percutaneous Magic screw is a minimally invasive treatment for acetabular posterior column fracture, which is difficult to operate. The screw can fix the fracture which is located at the middle and upper part of the acetabular posterior column.
ABSTRACT
Objective To investigate the position, direction and fixation range of retrograde screw of the posterior column of acetabulum based on CT data. Methods Totally 100 cases (50 males, 50 females) of normal adult pelvic CT data were collected from the First Affilated Hospital of Chongqing Medical University. The pelvis was reconstructed by Mimics 17. 0 software and imported into Geomagic Studio 2015 software. The virtual screw was placed in the posterior column from the ischial tuberosity to the iliac fossa, the maximum diameter, the entrance point, the exit point, the direction, safe fixation inclination angles of the screw were measured. The range of the screw fixing, the best fluoroscopic views and the easy-to-penetrate site of the screw in the posterior column were assessed. Results The safe corridor the posterior column of the acetabulum was similar to the "triangular prism" shape. The entrance point was located on the midline of the medial edge and lateral edge of the ischial tuberosity, which were ( 12. 99±1. 99) mm in male and ( 13. 26±2. 58) mm in female from farthest end of the ischial tuberosity. There were no stitistical significant differences between male and female ( P > 0. 05). The exit points was located at the iliac fossa, which were (23. 65 ± 2.42) mm in male and ( 24. 94 ± 2. 39) mm in female to the ipsilateral anterior sacroiliac joint line,and ( 19. 33±2. 60) mm in male and (17.63±2.00) mm in female to the arcus marginalis. The maximum diameters of screw were ( 17. 21±1. 41) mm in male and ( 15. 54±1. 51) mm in female. The angles between screw and coronal plane were ( 15. 00±4. 92)° in male and ( 12. 94±4. 72)° in female; the angles between screw and sagittal plane were ( 10. 52 ± 3. 04)° in male and ( 7. 72 ± 2. 99)° in female. The abore data had statistially significant differences between male and female ( P < 0. 05). Percutaneous retrograde screw could fix the acetabular posterior column fracture that below the 4. 0 cm proximal the horizontal plane of the femoral head center. The easy-to-penetrate sites were the junction of the acetabular posterior wall and the sciatic branch ,the middle part of the acetabulum, and below I. 0 cm of the highest point of greater sciatic notch. The tangential position of three lateral faces of the "triangular prism" were ilium oblique position 10° , the ilium Oblique position 60° and obturator Oblique position 60°. Conclusion The entrance point of the retrograde screw is located on the midline of the ischial tuberosity, which is 1. 3 cm from farthest end of the ischial tuberosity and the direction is forward inclination about 15° , external inclination about 10°. The acetabular posterior column fracture that below 4. 0 cm proximal plane to the femoral head center can be fixed by the retrograde screw.