The safety of transverse iliosacral screw fixation of longitudinal sacral fracture

Abstract

ObjectiveTo evaluate the safety of transverse iliosacral screw fixation of longitudinal sacral fracture.MethodsWe obtained CT scan data of the pelvis from 100 adults without any bony problems from September to December 2009. They were 52 males and 48 females, aged from 15 to 91 years (average, 43. 1 years) . We then reconstructed virtual three-dimensional models of the pelvis. The three-dimensional models were re-segmented through the sacral horizontal axis to obtain standard sagittal planes of the sacrum. To identify the safe zone for transverse screw fixation, we marked off the sacral margin on each sagittal plane. In simulation of the transverse screw ipsilateral fixation and transfixation, one single virtual cylindrical implant was inserted into the safe zone. The maximum diameter of the virtual cylindrical implant was measured.ResultsA 20. 0％ rate of sacral variation was observed (80 normal versus 20 deformed morphological sacrums). In ipsilateral fixation, the average screw diameter of variant S2 (14. 92 ± 2.57 mm) ＞normal S2 ( 12. 37 ± 1.84 mm) ( P =0. 000) ＞ normal S1 ( 11.87 ± 3.92 mm) ( P =0. 319 ) ＞ variant S3 (9. 30 ± 2. 00 mm) ( P =0. 000). In transfixation, the average screw diameter of variant S2 ( 13.63 ± 2. 68 mm) ＞ normalS2 (11.48 ±1.92mm) (P=0. 002) ＞ normal S1(10. 40 ±4.05 mm) (P=0.033) ＞variant S3 (7.95 ± 2. 26 mm) ( P =0. 001 ) . The maximum screw diameter of normal S2 showed a slightly negative correlation with that of normal S1, but there was no correlation between the maximum screw diameter for each sacral vertebra and the acetabulum diameter. The normal male S2 was significantly larger than the female one ( P ＜ 0.05), but there was no significant difference in S1 between genders ( P ＞ 0.05) .ConclusionsIn most Chinese people, the posterior pelvic ring could be fixed with 2 iliosacral screws of 6. 5 mm in diameter simultaneously in horizontal direction, but care should be taken because the safety zone is quite limited. A variant sacrum is not a contraindication for iliosacral screw fixation, but the entry point, the screw length and the sacral vertebra to be fixed must be determined after careful radiological evaluation. Key words: Sacrum; Fractures; Sacroiliac joints; Bone nails