**1. Introduction**

Spinopelvic dissociation (SPD) is associated with transverse sacral fractures, which cause the dissociation of the sacrum from the pelvis [1,2]. It is associated with 3% of transverse sacral fractures and 3% of sacral fractures are associated with pelvic ring injuries [3]. SPD is well known for its high mortality and comorbidities such as nerve root injuries [4]. When SPD is correctly diagnosed and appropriately treated, patient outcomes can be optimized [5]. However, a high level of consensus and a unified approach for dealing with this complex issue are lacking.

The traditional fixation methods for the posterior pelvic ring include tension band transiliac plate fixation, local plate fixation, open or percutaneous ilio-sacral screw fixation, and transiliac bars, which do not guarantee postoperative stability and may result in fixation failures [6,7]. In recent years, surgeons have used triangular osteosynthesis (TOS) in combination with the surgical technique of unilateral L5 fixation using S2AI or iliac screws for SPD treatment, and the literature indicates that these patients show satisfactory postoperative function and radiological outcomes [8]. With or without a combination of bilateral or dual iliac screw fixation techniques [9], TOS is a reliable form of fixation that enables early weight-bearing while preventing the loss of reduction [9–12]. In addition, compared with traditional surgical methods, its complication rate is low [3,5] (Figure 1A–F).

**Citation:** Su, P.-H.; Huang, Y.-H.; Yeh, C.-W.; Chen, C.-Y.; Lo, Y.-S.; Chen, H.-T.; Tsai, C.-H. What Are the Key Factors of Functional Outcomes in Patients with Spinopelvic Dissociation Treated with Triangular Osteosynthesis? *J. Clin. Med.* **2022**, *11*, 6715. https://doi.org/10.3390/ jcm11226715

Academic Editors: Steffen Rosslenbroich and Chang-Wug Oh

Received: 8 October 2022 Accepted: 11 November 2022 Published: 13 November 2022

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**Copyright:** © 2022 by the authors. Licensee MDPI, Basel, Switzerland. This article is an open access article distributed under the terms and conditions of the Creative Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ 4.0/).

**Figure 1.** (**A**–**F**) Pre- and postoperative radiography and CT images of a 21-year-old woman who fell from a bridge and developed bifrontal EDH, facial bone fractures, and bilateral sacral fractures with spinopelvic dissociation that were presented in the emergency room. (**A**) AP view of the pelvis on admission showing bilateral fracture lines on the sacrum; (**B**) lateral view of the sacral spine view on admission showing fracture lines on the sacrum, indicating displaced fragments over the fracture site; (**C**) axial CT view of the sacrum demonstrating bilateral fracture lines indicating U-type sacral fractures; (**D**) 3D CT view of the sacrum demonstrating a displaced U-shape sacral fracture (red arrows) and AO/OTA 54C3 type, Denis Zone II sacral fracture; (**E**) Postoperative AP pelvic view: the sacral fracture was stabilized by bilateral triangular osteosynthesis with S2AI screws. (**F**) Postoperative lateral view of the sacral spine: The trajectory of S2AI screws was set under O-arm navigation to obtain an optimal length. Abbreviations: EDH = epidural hematoma, CT = computed tomography, and AP = anteroposterior.

Currently, a radiographic assessment remains the standard peri-operative measurement for displacement and reduction in studies of pelvic fractures. However, there is still a lack of research investigating the relationship between peri-operative SPD and prognosis from the perspective of radiology in patients with SPD who underwent reduction and fixation by TOS using S2AI screws. Though the measurement of outcomes is difficult and the level of evidence in this area is poor, this article revealed three such methods for measuring radiographic displacement [11,13,14].

This study aimed to investigate the recovery time course and imaging parameters relevant to the functional recovery of patients with SPD treated by TOS.

#### **2. Materials and Methods**

*2.1. Patient Selection and Classification*

This is an observational, retrospective study. From August 2018 to September 2021, 29 patients with SPD were recruited. One was excluded due to severe spinal cord injuries, and five were lost to follow-up in our orthopedic clinic department. Complete series of

pre-and post-operative radiographs were collected from the remaining 23 patients who suffered pelvic fractures with SPD treated by TOS fixation using the S2AI screw fixation technique. To make the procedure more appropriate and to obtain an optimal length and deflection angle, we set the trajectory of the S2AI screws under O-arm navigation (Figure 2A–F) [15]. These patients were postoperatively followed-up for a minimum of one year in the clinic as a single cohort. The study protocol was approved by the Research Ethics Committee of the China Medical University Hospital, Taichung, Taiwan (protocol ID: CMUH108−REC3−144) and conducted in accordance with the ethical principles of the Helsinki Declaration. The inclusion criteria include skeletally mature patients who suffered pelvic fractures with SPD treated by TOS fixation. Based on the anatomic relationship between the fracture site and the sacral neural foramen, Denis et al. classified sacral fractures into three types. Roy-Camille et al. classified transverse sacral fractures of the Denis III zone into three subtypes based on the degree of displacement and the traumatic mechanism [16,17]. In this study, most patients were in Denis zones I and II.

**Figure 2.** (**A**–**F**) Pre- and postoperative radiography and CT images of a 56-year-old man who was hit by a vehicle and had right superior and inferior rami fractures, a right L5 transverse process fracture, and a right sacral fracture with spinopelvic dissociation. The associated injury included a left femoral shaft fracture, right femoral shaft segmental fracture, and left medial malleolar fracture. (**A**) Axial CT view of the sacrum on admission demonstrating fracture lines (yellow arrows) over the right L5 transverse process; (**B**) coronal CT view of the sacrum on admission demonstrating fracture lines (yellow arrows) over the right sacrum; (**C**) 3D CT view of the pelvis showing right superior and inferior rami fractures (yellow arrows), a right L5 transverse process fracture (yellow arrows), and a right AO/OTA 61C1.3 and 54B3 type, Denis Zone II, sacral fracture (yellow arrows); (**D**) with the assistance of O-arm navigation, the optimal trajectory of the S2AI screw was set (O-arm and Stealth Station S7 Surgical Navigation System, Stryker); (**E**) postoperative view of the inlet pelvis—the sacral fracture was stabilized by triangular osteosynthesis with S2AI screws, and the right superior rami fracture was reduced and fixed with a pre-contoured locking plate; (**F**) postoperative lateral view of the sacral spine. Abbreviations: CT = computed tomography.
