Critical distance of the sacroiliac joint for open reduction using screw fixation for traumatic sacroiliac joint diastasis: a retrospective study

Background: Osteosynthesis for sacroiliac joint (SIJ) diastasis using an iliosacral screw (ISS) and a trans-iliac-trans-sacral screw (TITSS) can be performed either by a closed or open method. However, a clear indication for open reduction remains controversial. Methods: Data on patients with unilateral traumatic SIJ diastasis who underwent ISS and TITSS fixation were retrospectively collected and separated into groups according to the reduction method: closed reduction group (C group) and open reduction group (O group). Demographic data and perioperative image assessments were compared between the groups. The critical distance of the SIJ was identified to elucidate the indication for open reduction of the diastatic SIJ. Results: Fifty-six patients met the inclusion criteria over a 3-year period. There was no significant difference in the reduction in quality of the pelvic ring injuries between the groups, according to Matta’s and Lefaivre’s criteria. The improvement in the SIJ distance was significantly greater in the O group than in the C group in the axial plane on multiplanar computed tomography (p = 0.021). This model predicted that a difference >3.71mm between the injured and healthy SIJ was recommended to undergo open reduction under an area under the curve of 0.791 (95% confidence interval 0.627–0.955, p = 0.004). Conclusions: Open reduction for SIJ diastasis might achieve better reduction quality than does closed reduction in the axial plane in selected cases. When the difference between the injured and healthy SIJ was wider than 3.71 mm, open reduction for the SIJ is recommended for satisfactory radiological outcomes.