Three-dimensional morphometry of the first two sacral segments and its impact on safe transiliac-transsacral screw placement.

Abstract

Abstract Introduction : Percutaneous screw fixation of the posterior pelvic ring is a popular technique to treat unstable pelvic ring lesions. This technique is practicable in both, the high-energy pelvic ring fractures, mostly in the young population as well as the osteoporotic fractures in the elderly. Risk of the transiliac-transsacral screw positioning is that the critical area of nerve root exit has to be passed twice. For secure screw placement, without causing iatrogenic neurovascular injuries, the knowledge of distances to the narrowest areas is essential. Purpose of this anatomical study was to examine the optimal intraosseous screw placement for the first two sacral segments. Material/Methods : Images of uninjured pelves from 50 patients (64-line CT scanner) were evaluated. Then virtual transiliac-transsacral srews were positioned into the first two sacral segments. The distance from the screws’ entrance points at the ilium s alar bone to the narrowest portion of the whole pedicle as well as the height and width in this area were measured. Descriptive statistics were used and gender related differences were evaluated using student T-test. Results : For the first sacral segment the distance to the narrowest zone amounted in mean 62.75 mm respectively 63.31 mm, depending on the selected way of measurement. For the second segment the mean distance to the neuroforamina was on average 50.61 mm, respectively 51.54 mm. The average height in S1 measured 25.88 mm and the average width 25.49 mm. The average height for S2 was 17.54 mm and the average width 17.61 mm. We could not find any statistically significant gender correlation for the measured distances. Conclusion : Results of this anatomical study may help in performing a safe surgical procedure.