The aim of surgical treatment of unstable pelvic fractures is to correct the deformity, restore the anatomical structure of the pelvic ring, and promote early functional exercise. Previous studies have shown that the anterior and posterior rings account for 40% and 60% of the stability of the pelvis, respectively . Therefore, simultaneous fixation of the anterior and posterior pelvic rings is often necessary to treat unstable pelvic fractures.
Treatment of posterior pelvic ring fractures
Surgical fixation options for managing traumatic disruptions to the posterior pelvic ring included percutaneous sacroiliac screw fixation, plate fixation, and lumbosacral iliac screws. However, the most popular operative treatment option at present is percutaneous sacroiliac screw fixation, as it is associated with less trauma, less blood loss, and earlier mobilization than other treatments . The fixation of double screws into the sacrum is associated with an increased risk of nerve injury due to significant variation in sacral anatomy .
Sacroiliac joint screw placement in the S1 vertebral body is the standard technique for posterior ring fixation [19, 23, 24]. Mears et al. showed that a single sacroiliac screw fixation can restore biomechanical stability similar to that of the complete pelvis in cadaveric models, under 10–350 N of vertical compressive load . However, Yinger suggested that in unstable pelvic fractures, the placement of two sacroiliac joint screws increases stability against rotation and vertical displacement when the pelvic ring is loaded to 1000 N . It is likely that the study by Mears et al. did not detect a difference between the techniques due to the use of inadequate vertical compressive load. In our study, we found no difference in anterior and posterior pelvic ring stability between the single- and double-screw fixation techniques when axial loading was less than 200 N; There is no differences between the single- and double-screw fixation in posterior stability under loads of 400 N and 800 N. However, for anterior pelvic ring stability, with loads of 400 N and 800 N, significant differences emerged between the two techniques, suggesting the superiority of the double-screw fixation technique.
Treatment of anterior pelvic ring fractures
Traditionally, open reduction and plate fixation is the optimal treatment for anterior pelvic ring fractures, providing excellent stability and early mobilization. However, disadvantages include long operation times, large wound sizes and periosteal stripping areas, and increased bleeding. In addition, the risk of infection and re-operation exists, especially in obese patients or patients with a history of abdominal surgery. Furthermore, another technique employed in the treatment of these fractures is channel screw fixation, but it requires extensive training and a high level of surgical skill.
To address these treatment challenges, in 2009, Kuttert et al. performed the first anterior ring fixation for unstable pelvic fractures using INFIX . INFIX has since become a popular treatment technique for unstable pelvic fractures, with reported benefits including reduced soft tissue injury, less blood loss, and low incidence of intraoperative iatrogenic nerve injury [7–9]. Studies investigating the biomechanics, anatomy, and clinical outcomes of INFIX have found that INFIX may provide adequate pelvic stability and achieve good clinical outcomes, despite its associated complications [27–30].
There are no data on the functional outcome of INFIX plus single versus INFIX plus double sacroiliac screw fixation technique for unstable pelvic ring injury (AO/OTA type C). We found that INFIX plus double sacroiliac screw fixation offered significantly better stability in the anterior pelvis than INFIX plus single sacroiliac screw fixation, under 400–800 N of axial loading. This result further supports the conclusion that the addition of a second screw improved the stability of the pelvis, which is consistent with the results of previous studies [18, 26, 31].
In addition, to investigate whether the INFIX plus double sacroiliac screw fixation technique improved functional outcomes clinically, 19 patients with unstable pelvic ring injury (AO/OTA type C) were retrospectively analyzed and followed up. We found that all fractures healed by the 6-month follow-up visit, with one patient who received INFIX plus single sacroiliac screw fixation experiencing non-union of the pubic ramus fracture.
In terms of joint stability, we did not find greater joint instability with single-screw fixation in our biomechanics study, but we did observe greater joint instability in the retrospective clinical analysis. In terms of nerve injury, two patients developed anterolateral numbness in the affected thigh, which resolved by three months post implant removal. Fang et al. reported an LFCN paralysis rate of 48.3% , which was much higher than the rate in our study. The reason for our finding may be improved surgical execution of the INFIX technique in the last decade and our use of pedicle screws with a smaller diameter (6.5 mm), compared with those used in Fang et al.’s study (7.3–10 mm). The limitations of this study is a retrospective study with a small sample size. A multi-center prospective studies with large sample size should be conducted in future study.