The Technique Of Buttress Plate Placement In The Postrior Column Of The Acetabulum

Objective: Most acetabulumm fractures involved in the posterior column and posterior wall need open reduction and internal fixation (ORIF), and the most frequently used internal fixation technique is acetabular posterior column plate technique during operation. Sometimes serious complication occurs during internal fixation of the fractured fragment, such as screw penetrating the joint surface, injuring important blood vessel and nerve, especially palcing screw on the middle region of the posterior column is dangerous. The quantitative anatomic documents about how to fix firmly and to prevent serious complication such as screw penetrating the joint surface when using cetabular anterior column plate technique are few at present. We make the serial cross-sections of the acetabular posterior column with cadaveric adult antiseptic specimens and study it, determine the angle of inclination and the mean length of screw placed on the posterior column, and solve the problem of screw penetrating the joint surface easily when placing the screw on the middle region of the posterior column.Methods: 10 cadaveric adult antiseptic specimens were prepared. Determine superior acetabular margin, inferior acetabular margin and make the serial cross-sections of the acetabular posterior column. Measure the the width of posterior column, the width of acetabulum and the ratio of the width of acetabulum to the width of posterior column, and measure the angle of inclination and the mean length of screw on all entry points, put all data into software SPSS 10.0 for statistics process. Results:1. Superior acetabular margin and inferior acetabular margin: The projection of superior acetabular margin on the surface of posterior column is 10.2±2.7 mm higher than the top of greater sciatic notch, the projection of inferior acetabular margin on the surface of posterior column is 11.5±2.6 mm higher than the lower margin of the ischial spine, the distance from the projection of superior acetabular margin to the projection of inferior acetabular margin on the surface of posterior column is 54.7±4.8 mm.2. The width of posterior column, the width of acetabulum and the ratio of the width of acetabulum to the width of posterior column on each cross-section. The width of posterior column, the width of acetabulum and the ratio of the width of acetabulum to the width of posterior column on cross-section A is 52.2±4.4 mm, 0 mm and 0% respectively; The width of posterior column, the width of acetabulum and the ratio of the width of acetabulum to the width of posterior column on cross-section B is 40.8±2.2 mm, 19.2±1.3 mm and 47.1 % respectively; The width of posterior column, the width of acetabulum and the ratio of the width of acetabulum to the width of posterior column on cross-section C is 39.3±4.5 mm, 22.4±1.5 mm and 56.9% respectively; The width of posterior column, the width of acetabulum and the ratio of the width of acetabulum to the width of posterior column on cross-section D is 38.1±3.6 mm, 17.6±1.1 mm and 46.2% respectively; The width of posterior column, the width of acetabulum and the ratio of the width of acetabulum to the width of posterior column on cross-section E is 48.2±5.1 mm, 0 mm and 0% respectively. To link the inner endpoint of cross-sectionA, B, C, D and E form the absolute dangerous region of the acetabulum, it means if placing screw perpendicular to the surface of posterior column on the region, the screw should penetrate into the joint surface.3. The angle of inclination and the mean length of screw of each entry point on cross-section B, C and D. On cross-section B, the angle of inclination and the mean length of screw of entry point BO is 41° and 44 mm respectively; the angle of inclination and the mean length of screw of entry point B1 is 66° and 42.2 mm respectively; the angle of inclination and the mean length of screw of entry point B2 is 91° and 59.5 mm respectively; the angle of inclination and the mean length of screw of entry point B3 is 107° and 64 mm respectively; the maximum angle of inclination and the mean length of screw of entry point B4 is 123° and 65.47 mm respectively; the minimum angle of inclination and the mean length of screw of entry point B4 is 109° and 59 mm respectively. On cross-section C, the angle of inclination and the mean length of screw of entry point CO is 39° and 39 mm respectively; the angle of inclination and the mean length of screw of entry point C1 is 57° and 36 mm respectively; the angle of inclination and the mean length of screw of entry point C2 is 74° and 36 mm respectively; the angle of inclination and the mean length of screw of entry point C3 is 90° and 36 mm respectively; the angle of inclination and the mean length of screw of entry point C4 is 106° and 76 mm respectively. On cross-section D, the angle of inclination and the mean length of screw of entry point DO is 42° and 35.5 mm respectively; the angle of inclination and the mean length of screw of entry point D1 is 61° and 33 mm respectively; the angle of inclination and the mean length of screw of entry point D2 is 81° and 32 mm respectively; the angle of inclination and the mean length of screw of entry point D3 is 100° and 31 mm respectively; the angle of inclination and the mean length of screw of entry point D4 is 120° and 74 mm respectively.Conclusion: Acetabular posterior column plate technique: on the outer 1/4 region, outer-middle 1/4 region, inner-middle 1/4 region and inner 1/4 region of the acetabulum region, screw-posterior column angle is 40°～60°, 60°～75°, 75°～90° and 90°～parallel to the square area respectively, and the length of the screw is 30mm.