CT Imaging Anatomical Study of Percutaneous Magic Screw Fixation for Acetabular Posterior Column Fracture

Abstract 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.