No abstract

Background: The infra-acetabular corridor is quite narrow, which makes a challenge for the orthopedists to insert the screw. This study aimed to explore the relationship between the infra-acetabular corridor diameter (IACD) and the minimum thickness of medial acetabular wall(MTMAW), and to clarify the way of screw placement. Methods: The Computed tomography (CT) data of 100 normal adult pelvises (50 males and 50 females respectively) were collected and pelvis three-dimensional(3D) reconstruction was performed by using Mimics software and the 3D model was imported into Geomagic Studio software. The perspective of acetabulum was carried out orienting from iliopubic eminence to ischial tuberosity and the IACD was measured by placing virtual screws which was vertical to the corridor transverse section of "teardrop". The relationship between IACD and MTMAW was analyzed. When IACD was ≥ 5 mm, 3.5mm all-in screws were placed. When IACD was < 5 mm, 3.5mm in-out-in screws were placed. Results: The IACD of males and females were (6.15 ± 1.24) mm and (5.42 ± 1.01) mm and the MTMAW in males and females were (4.40 ± 1.23) mm and (3.60 ± 0.81)mm respectively. The IACD and MTMAW in males were significantly wider than those of females (P < 0.05), and IACD was positively correlated with MTMAW (r = 0.859), the regression equation was IACD = 2.111 + 0.917 MTMAW. In the all-in screw group, 38 cases (76%) were males and 33 cases (66%) were females respectively. The entry point was located at posteromedial of the apex of iliopubic eminence, and the posterior distance and medial distance were (8.03±2.01)mm and (8.49±2.68)mm respectively in males. As for females, those were (8.68±2.35)mm and (8.87±2.79)mm respectively. In the in-out-in screw group, 12 cases (24%) were males and 17 cases (34%) were females, respectively. The posterior distance and medial distance between the entry point and the apex of iliopubic eminence were (10.49±2.58)mm and (6.17±1.84)mm respectively in males. As for females, those were (10.10±2.63)mm and (6.63±1.49)mm respectively. The angle between the infra-acetabular screw and the sagittal plane was medial inclination (0.42 ± 6.49) °in males, lateral inclination (8.09 ± 6.33) °in females, and the angle between the infra-acetabular screw and the coronal plane was posterior inclination (54.06 ± 7.37) °. Conclusions: The placement mode of the infra-acetabular screw(IAS) can be determined preoperatively by measuring the MTMAW in the CT axial layers. Compared with all-in screw, the in-out-in screw entry point was around 2mm outwards and backwards, and closer to true pelvic rim.

Background: Research into minimally-invasive fixation of acetabular posterior column fracture has mostly focused on anatomic measurement through the ischial tuberosity in a retrograde manner, and few anatomic studies have been carried out on anterograde percutaneous Magic screws. The purpose of this paper was to discuss the entry point, entry direction and fixation range of Magic screws for fixation of acetabular posterior column fracture.Method: Materialise’s Interactive Medical Image Control System (Mimics) 19.0 software was used to carry out three-dimensional (3-D) reconstruction based on the Computed tomography (CT) data of the pelvises of 100 cases. A virtual Magic screw was placed in the acetabular posterior column, and the screw entry point, entry direction, length, diameter, safety range and fixation range were determined. Osteotomy modeling was performed on the acetabular posterior column with virtual Magic screw fixation, and the changing law of the width of the screw channel was observed. The narrowest distance and position between the screw edge and the acetabulum were measured.Results: The bone entry point of the Magic screw on the posterior side to the anterior inferior iliac spine and cephalad side to the acetabular top for the males were 33.32 ± 5.52 mm and 13.42 ± 3.68 mm, respectively; and those for females were 33.94 ± 5.43 mm and 9.11 ± 3.82 mm, respectively. The screw for males had a back rake angle of 57.37 ± 6.53° and a leaning inside angle of 52.12 ± 5.61°, with an angle of 15.16 ± 3.45° to the iliac wing. For females, those angles were 55.61 ± 7.94°, 51.53 ± 5.59° and 9.76 ± 3.69°, respectively. The maximum screw diameter was 6.97 ± 0.98 mm for males and 6.39 ± 0.85 mm for females. The screw length was 76.73 ± 9.20 mm for males and 63.64 ± 8.37 mm for females. The safety ranges of back rake angle and leaning inside angle of the 5.5 mm diameter screws for the males were 7.18 ± 3.32° and 9.42 ± 3.96°, respectively, and those of 5.2 mm diameter screws for females were 8.39 ± 2.83° and 10.37 ± 3.92°, respectively. For 60% of the male specimens, the screw fixation range was above the acetabular top, with a length of 60.45 ± 5.92 cm; and for 40% of the male specimens, the screw fixation range was below the acetabular top, with a length of 50.68 ± 6.49 cm. For females, 24% of the specimens were above the acetabular top, with a length of 52.19 ± 7.76 cm; and 76% of the specimens were below the acetabular top, with a length of 38.40 ± 4.35.Conclusion: Percutaneous Magic screws provide a minimally-invasive fixation method for acetabular posterior column fracture with high surgical difficulty, and can be used to fix fractures located in the middle and upper segment of the posterior column.

Background The infra-acetabular corridor is quite narrow, which makes a challenge for the orthopedists to insert the screw. This study aimed to explore the relationship between the infra-acetabular corridor diameter (IACD) and the minimum thickness of medial acetabular wall (MTMAW), and to clarify the way of screw placement. Methods The Computed tomography (CT) data of 100 normal adult pelvises (50 males and 50 females respectively) were collected and pelvis three-dimensional (3D) reconstruction was performed by using Mimics software and the 3D model was imported into Geomagic Studio software. The perspective of acetabulum was carried out orienting from iliopubic eminence to ischial tuberosity and the IACD was measured by placing virtual screws which was vertical to the corridor transverse section of “teardrop”. The relationship between IACD and MTMAW was analyzed. When IACD was ≥5 mm, 3.5 mm all-in screws were placed. When IACD was < 5 mm, 3.5 mm in-out-in screws were placed. Results The IACD of males and females were (6.15 ± 1.24) mm and (5.42 ± 1.01) mm and the MTMAW in males and females were (4.40 ± 1.23) mm and (3.60 ± 0.81) mm respectively. The IACD and MTMAW in males were significantly wider than those of females (P < 0.05), and IACD was positively correlated with MTMAW (r = 0.859), the regression equation was IACD = 2.111 + 0.917 MTMAW. In the all-in screw group, 38 cases (76%) were males and 33 cases (66%) were females respectively. The entry point was located at posteromedial of the apex of iliopubic eminence, and the posterior distance and medial distance were (8.03 ± 2.01) mm and (8.49 ± 2.68) mm respectively in males. As for females, those were (8.68 ± 2.35) mm and (8.87 ± 2.79) mm respectively. In the in-out-in screw group, 12 cases (24%) were males and 17 cases (34%) were females, respectively. The posterior distance and medial distance between the entry point and the apex of iliopubic eminence were (10.49 ± 2.58) mm and (6.17 ± 1.84) mm respectively in males. As for females, those were (10.10 ± 2.63) mm and (6.63 ± 1.49) mm respectively. The angle between the infra-acetabular screw and the sagittal plane was medial inclination (0.42 ± 6.49) °in males, lateral inclination (8.09 ± 6.33) °in females, and the angle between the infra-acetabular screw and the coronal plane was posterior inclination (54.06 ± 7.37) °. Conclusions The placement mode of the infra-acetabular screw (IAS) can be determined preoperatively by measuring the MTMAW in the CT axial layers. Compared with all-in screw, the in-out-in screw entry point was around 2 mm outwards and backwards, and closer to true pelvic rim.