Anatomic study of dorsal plate-screw fixation in sacral fractures

Objective To explore the security of dorsal plate-screw fixation in transverse or oblique sacral fractures. Methods Thirty fresh adult corpses (15 males and 15 females, the age ranged from 38 to 82 years, mean 65 years) were studied. The points of sacrum were separately defined as: label point on the sacrum of 30 cases of pelvic specimen were made and the points of sacrum were separately defined as: O points was the entry point of the sacral screw; D_1 was the screw trajectory's length when fixing to the medial; D_2 was the screw trajectory's length when vertical fixing; D_3 was the screw trajectory's length when fixing to the lateral; α was the maximum deviation angle of sacrum at cross-section when fixing to the medial; β was the maximum deviation angle of sacrum at cross-section when fixing to the lateral. Results For the S_1 screw, the average values of D_1,D_2,D_3, α and β were (38.73±5.29) mm, (31.15±4.68) mm, (41.47±6.18) mm, 31.88°±4.32° and 34.31°±5.12° respectively. For the S_2 screw, the average values of D_1, D_2, D_3, α and β were (28.53±2.19) mm, (23.95±2.59) mm, (34.69±5.13) mm, 14.70°±3.54° and 20.48°±5.35° respectively. For the S_3 screw, the average values of D_1, D_2, D_3, α and β were (30.62±3.15) mm, (17.18±3.51) mm, (24.66±5.13) mm, 52.00°±7.55° and 39.00°±5.50° respectively. For the S_4 screw, the average values of D_1, D_2, D_3, α and β were (23.21±4.14) mm, (9.07±2.20) mm,(14.52±3.51) mm, 18.47°±4.42° and 10.23°± 2.69° respectively. Conclusion It is the optimal trajectory for S_1 screw to entry at O_1 points, and be parallel to L_5 spinous process. The S_2, S_3 and 54 screw's entry points respectively are O_2, O_3 and O_4 points and the screw placement parallel to the upper endplate at sagittal plane. The optimal screw placement at cross-section is leaned to lateral less than 20.48°±5.35° for S_2 screw, leaned to medial less than 52.00°±7.55° for S_3 screw, and to lateral less than 18.47°±4.42° for S_4 screw respectively. Key words: Sacrum;  Fractures;  Bone screws;  Dissection