Evolution of the reduction technique for unstable pelvic ring fractures: a narrative review

Abstract

Unstable pelvic ring fractures are associated with high mortality and morbidity, and the quality of reduction is critical to the prognosis. While previous reviews have examined general fracture reduction techniques, there is limited focus on the specific advancements and challenges in the reduction technique of unstable pelvic ring fractures. The pelvic fracture reduction technique has undergone a four-stage evolution: open reduction, conventional closed reduction, navigation-assisted closed reduction, and robot-assisted automatic closed reduction. This review discusses and compares the features, effectiveness, and safety of each reduction technique. Open reduction improves clinical outcomes compared to nonsurgical management; however, it is no longer commonly practiced due to its association with extensive soft tissue damage. Although conventional closed reduction is minimally invasive and reduces intraoperative blood loss, surgical duration, and the length of hospital stay, frequent fluoroscopy is required to assess the reduction position, imposing a high risk of radiation exposure. Computer-aided navigation technology has advanced closed reduction techniques by allowing better visualization of the fracture site and surgical instruments, thereby enhancing the quality of pelvic fracture reduction and reducing radiation exposure. The recently developed robot-assisted automatic reduction technique relieves the burden on orthopedic surgeons and further reduces intraoperative radiation exposure. Future advancements in the pelvic reduction technique may involve big data-based intelligent reduction to enable broader indications such as bilateral pelvic fractures.

Background

Unstable pelvic ring fractures, characterized by the loss of posterior osteoligamentous integrity, typically arise from high-energy trauma in young individuals and low-energy injuries in older populations. Despite their relatively low prevalence among all skeletal injuries, unstable pelvic ring fractures can be life-threatening [1]. A 10 year epidemiological study from 2008 to 2017 revealed that the mean annual mortality rate of unstable pelvic fractures was 5.5% and increased to 14.3% when the fractures had an Injury Severity Score ≥ 16 [2]. Most unstable pelvic ring fractures feature complex spatial displacement. The primary treatment goal is to achieve fracture reduction and fix the fragments to restore pelvic stability. Patients with an unsatisfactory reduction often experience chronic pain, deformity, lower-limb dysfunction, and poor functional recovery [3,4,5]. Previous studies have shown that excellent reduction with a residual displacement of < 5 mm is the only predictor of favorable functional results [6, 7]. Therefore, accurate reduction is crucial for the successful treatment of unstable pelvic ring fractures.

The irregular shape of the pelvis, which contains complex nervous and vascular structures, makes anatomical reduction of displaced pelvic fractures particularly challenging. In recent decades, the surgical treatment of pelvic fractures has gradually evolved from open surgery to minimally invasive surgery (MIS), and the progress in navigation and robotic technologies has further advanced reduction techniques for pelvic fractures. Although general fracture reduction technique has been discussed [8, 9], a focused review on the evolution of the reduction technique for unstable pelvic ring fracture is still lacking. This review aimed to fill this knowledge gap by describing the evolution, safety, effectiveness, and future direction of surgical reduction techniques for unstable pelvic ring fractures. We performed a systematic search of the literature databases PubMed and Embase on April 16, 2024, to identify articles reporting pelvic fracture reduction. The search and screening strategies are displayed in Supplementary Table 1 and Supplementary Fig. 1, respectively. A total of 58 articles were included in this review.

Pelvic anatomy and fracture classification

The pelvis ring is composed of a sacrum and two innominate bones, each of which is a fusion of the ilium, ischium, and pubic bones. The ring is formed by connecting the two innominate bones at the pubic symphysis and to the sacrum at the sacroiliac (SI) joints [10] (Fig. 1a). The pelvic ring is stabilized by the ligaments at the pubic symphysis and SI, and sacrospinous, sacrotuberous, lumbosacral, and iliolumbar ligaments (Fig. 1b) [11]. An unstable pelvic ring may disrupt the major ligaments and cause injury to the soft tissue, internal organs, and vasculature of the pelvis. The Young–Burgess classification system defines an unstable pelvic ring as anterior–posterior compression type II/III, lateral compression type III, vertical shear, or a combined mechanism. In the AO/Tile classification system, types B (partially unstable) and C (completely unstable) describe an unstable pelvic ring [12].

Fig. 1

Pelvic anatomy. a Osseous anatomy of the pelvic ring. b Interosseous ligaments maintaining pelvic stability

Reduction techniques

Nonsurgical methods, such as bed rest, skeletal traction, pelvic slings, and hip spica casts, are often associated with high risks of nonunion, malunion, and complications involving multiple organs because of requiring a long period of recumbency [3]. Thus, early fixation of the posterior elements is crucial for the effective treatment of unstable pelvic ring fractures. The development of reduction techniques for unstable pelvic fractures has progressed through four stages: open reduction, conventional closed reduction, computer navigation-assisted closed reduction, and robot-assisted automatic closed reduction.

Open reduction

In the mid-nineteenth century, the open reduction and internal fixation (ORIF) technique was introduced for the management of unstable pelvic fractures [13]. This technique requires the surgeon to expose the pelvis, manually manipulate the displaced fracture segments, and fix the repositioned segments using plates and screws. When pelvic fractures involve symphysis disruptions, exposure of the pubis covering the pubic tubercle is usually adequate. If anterior pelvic injuries involve ramus fractures and symphysis disruption, exposure needs to be extended up to the pelvic brim through a midline incision to achieve fixation above the acetabulum [14]. Posterior fracture reduction can be achieved by either a posterior or anterior approach. In the posterior approach, the SI joint is exposed with the patient in the prone position. As the SI joint is sheltered from the posterior part of the ilium, direct visualization of the final reduction is impossible. In the anterior approach, the lateral window of the ilioinguinal approach can be used with the patient in the supine position. This approach allows a direct view of the SI joint; however, the proximity of the L5 nerve root to the SI joint poses a significant risk [14]. When reducing posterior pelvic fractures, proximal tibial or distal femoral skeletal traction is usually applied preoperatively in addition to intraoperative manipulative treatment. The application of skeletal traction facilitates the reduction process intraoperatively and prevents further displacement of the hemipelvis [15].

Compared with nonsurgical management, such as prolonged traction and external pelvic fixation, ORIF yields superior reduction quality, better functional score, earlier mobilization, and a shorter length of hospital stay but at the price of high complication rates [15,16,17,18,19,20]. In a prospective cohort study, Kabak et al. reported an excellent and good reduction quality rate of 85% using Matta’s criteria, with complication rates of 17.5% for superficial infections, 12.5% for soft tissue contusion, and 17.5% for neurological deficiency in 40 cases of type C pelvic ring fracture [15]. Mardanpour et al. retrospectively reviewed the clinical outcomes of 38 patients with type B and C fractures and found that the rate of excellent and good reduction was 57.9%, and the rate of postoperative complications, including deep wound infection, lateral injury of the cutaneous nerve of the thigh, pelvic obliquity, and/or urinary tract infection, was 26.3% [19]. Korovessis et al. reported a 90% satisfactory reduction (good and very good) rate in 74 patients with unstable pelvic fractures and the complication rates of 4.1% for wound dehiscence, 12.6% for urinary tract infection, 31.1% for deep vein thrombosis, and 8.1% for hematomas [20].

Three-dimensional (3D) printing technology can generate a 1:1 scale physical model of the patient’s pelvis in vitro, allowing orthopedic surgeons to thoroughly evaluate fractures in 3D and simulate reduction manipulation at the preoperative planning stage and thus improves the preoperative planning for ORIF [21, 22]. Additionally, orthopedic surgeons can select appropriate plates and screws that match the bone surface based on the 3D model to ensure the accuracy and mechanical strength of the reduction. Li et al. demonstrated that their 3D-printed model not only showed the bone structure, but also presented the soft tissues and vasculature such as the arteries and veins; thus, they were able to understand the relative position of the fracture to the surrounding tissues and maximally avoid soft tissue damage during surgery [22]. In a meta-analysis, Wang et al. found that using 3D printing technology in ORIF significantly shortened the operative time, reduced intraoperative blood loss and rates of complications, enhanced the quality of fracture reduction, and improved functional recovery [23].

ORIF can improve clinical effectiveness but often cause excess blood loss and an increased risk of infection and complications [19]. Although with 3D printing-mediated better preoperative planning, ORIF is not practiced frequently because of its traumatic nature and heavy mental and physical burdens on surgeons. According to an epidemiological study of trends in pelvic surgery from 2005 to 2017, the number of closed reduction and percutaneous fixation (CRPF) surgeries of the pelvic ring increased by 1116%, whereas the number of ORIF surgeries increased by only 185% [24].

Conventional closed reduction

In the past two decades, the CRPF technique has become the mainstream surgical treatment for unstable pelvic fractures, with percutaneous SI screw fixation typically performed [25,26,27,28,29]. The reduction methods in the CRPF technique have the following features: (1) ipsilateral lower-limb traction may be applied preoperatively when vertical displacement exists; (2) the intraoperative reduction process is achieved through manual manipulation of the fragments during screw insertion or plate compression; (3) when the fracture fragments are manipulated from the displaced position to the anatomic position, intraoperative fluoroscopy is routinely used to confirm the position, and external fixation tools, such as forceps, ball spike pushers, and clamps, may be used to temporarily maintain the reduction before definite fixation [7, 28, 30].

Numerous retrospective cohort studies have compared the safety and effectiveness of closed versus open reduction. Lindsay et al. found that closed reduction achieved a higher percentage of excellent reduction quality (89%) than did open reduction (60%) in 113 patients with type C1 fractures [7]. In 52 patients with type B pelvic fractures, Wang et al. reported that compared with the open reduction group (n = 26), the closed reduction group (n = 26) had significantly less intraoperative blood loss (57.7 vs. 186.5 mL, P < 0.001), shorter operation duration (57.9 vs. 114.1 min, P < 0.001), shorter length of hospital stay (10.2 days vs. 17.9 days, P < 0.001), greater proportion of excellent and good reduction quality at the 6 month follow-up (80.8 vs. 65.4%), and the same incidence rate of adverse events (7.7 vs. 7.7%) [26]. Abou-Khalil et al. compared the clinical outcomes of ORIF versus CRPF in 36 cases of unstable pelvic ring fractures and found that the CRPF group had significantly less intraoperative blood loss (300 vs. 500 mL, P < 0.05) and similar functional scores, operation duration, length of hospital stay, infection rate, and neurological injury incidence rate compared with the ORIF group [31]. A comparative study of patients undergoing CRPF (n = 62) versus ORIF (n = 66) demonstrated that the CRPF group had a significantly shorter operation duration (103 vs. 152 min, P = 0.001), less blood loss (50 vs. 250 mL, P < 0.001), and a shorter postoperative length of stay (8 vs. 15 days, P < 0.001) than did the ORIF group; however, the reduction quality (excellent rate CRPF 48% vs. ORIF 50%) and complication rate (CRPF 4.8% vs. ORIF 7.6%) were similar in the two groups [32]. These studies revealed that the CRPF approach could achieve a quality of fracture reduction noninferior to that with ORIF without increasing the incidence of complications and is associated with clear advantages in reducing blood loss, operation duration, and length of hospital stay.

The most obvious advantage of closed reduction over open reduction is the avoidance of extensive soft tissue damage during surgery; however, repositioning the fractured fragments to the right place is difficult because the fracture site is invisible during closed reduction. Surgeons must continue trying until a satisfactory reduction is achieved, which necessitates repeated fluoroscopy and increases the risk of radiation exposure. Although 3D printing technology allows surgeons to plan a personalized reduction strategy preoperatively and thus simplify the closed reduction process and shorten the operation duration and fluoroscopy time in CRPF surgery [33, 34], the challenge of maintaining the reduction position for a long period of time for fixation remains daunting. To overcome this challenge, reduction frames that connect the pelvis to the operating table have been developed, such as Matta’s frame and the semicircular Starr frame (Fig. 2) [35, 36].

Fig. 2

Reduction frames. a Matta’s frame (diagram adopted from the literature [35]. b Starr frame (diagram adopted from the manufacture’s website https://www.starrframe.com/products/starr-frame/)

The basic principle of these table-skeletal frames is to securely fix the intact hemipelvis to the operating table and facilitate multiplanar reduction of the injured hemipelvis by manipulating the external fixator pins attached to the frame. In addition to facilitating the reduction process, the frames allow surgeons to fix the fracture in a controlled manner with the pelvis remaining in the reduced position. These reduction frames were invented mainly for closed reduction; however, they are also used as adjuncts in open surgery when closed reduction fails or when open osteotomies are indicated for pelvic malunion.

Matta et al. reported successful treatment of acute and malunion fractures using the Matta frame since 2002. A retrospective cohort study on 22 patients with type B or C fractures undergoing Starr frame-assisted closed reduction has shown an excellent and good reduction quality rate of 86%, average operative time of 137.0 ± 43.7 min, and average X-ray fluoroscopy time of 24.3 ± 11.2 s [37]. In another retrospective study involving 54 patients with Tile C1 fracture, Deng et al. used the Starr frame for intraoperative reduction and achieved excellent fracture reduction [38]. Chen et al. integrated the Starr frame with unlocking and traction apparatuses to develop a new reduction frame called the unlocking closed reduction technique (UCRT) [39]. This modified Starr frame is effective for irreducible, unilateral, and vertically displaced pelvic ring disruption because it can resolve fracture locking or sticking, which is often present in displaced posterior pelvic ring fractures. In a retrospective cohort study on 97 patients with type B or C fractures, Luo et al. reported a successful closed reduction rate of 91.8% using UCRT and an excellent or good reduction quality rate of 92.1% [40].

The reduction frames relieve the orthopedic surgeons’ burden in the closed reduction of unstable pelvic ring fractures, however, frequent intraoperative 2D fluoroscopy is still required to evaluate reduction quality. Therefore, the risk of radiation exposure remains high, especially for junior surgeons, who often have limited experience in matching 2D fluoroscopic images with 3D pelvic structures.

Navigation-assisted closed reduction

Computer-aided navigation is a plausible solution for improving the visualization of the 3D pelvic geometry. In pelvic fracture surgery, navigation systems have mainly been used to assist in precise screw placement rather than to facilitate accurate fracture reduction [41, 42]. Navigation systems have been combined with reduction frames to achieve pelvic fracture reduction. Zhao et al. developed a computer-aided pelvic reduction system that combined the intraoperative CT navigation technology with a modified Starr frame. The operating principle was that a 3D model of the patient and the reduction frame was constructed based on the first intraoperative CT scan, and the target reduction position of the injured hemipelvis was determined using the mirror model of the uninjured hemipelvis. Then, the 3D processing software planned and calculated each step of the reduction process based on the target reduction position. The actual reduction manipulation was performed following the calculated steps, and the software constructed the 3D model of the actual reduction position based on a second intraoperative CT scan and assessed the residual translational and rotational differences between the actual and target reduction positions. Zhao et al. evaluated the effectiveness and safety of this system in 10 patients with unstable pelvic fractures and found that the average translational residual displacement was 2.38 mm, and the average rotational maximum residual displacement was 1.55 degrees, indicating that the reduction system had high accuracy. No complications, such as nerve or vascular injuries, were observed [43].

Similarly, Li et al. combined the HoloSight Navigation System with the UCRT frame to develop a mixed-reality surgical navigation (MRSN) system. The system created a voxel model of the pelvis and infrared reflecting trackers based on preoperative 3D CT images and then transferred the model to the HoloSight Navigation System. The target reduction position was planned by mirroring the healthy hemipelvis. Reduction was achieved by translating or rotating the injured hemipelvis to the target position by manipulating the long screw that grasped the pelvis. The clinical outcomes of 30 patients with type C pelvic fractures who underwent MRSN treatment showed an excellent reduction rate of 96.6% and no cases of postoperative complications [44]. Li et al. further found that using the MRSN system to treat unstable pelvic fractures significantly decreased the reduction time (45 vs. 104 min, P < 0.001) and intraoperative fluoroscopy frequency (43 vs. 146 times, P < 0.001) and improved the reduction quality (excellent reduction quality rate: 95 vs. 65%) compared with the treatment without using the MRSN system [45].

The combination of navigation technology and reduction frames reduces radiation exposure and enhances reduction quality by enabling 3D visualization of the pelvis and reducing the surgeon’s burden of reduction manipulation. However, the bulky structure of the frame does not offer flexibility in reducing the multidimensional displaced fragments. In addition, the reduction technique based on a combination of navigation and reduction frame still requires surgeons to manually move the fracture fragment.

Robot-assisted automatic closed reduction

Orthopedic robotic systems have developed rapidly in recent decades, and these systems are used at diverse anatomical sites and indications, including the knee joint, hip, spine, trauma, and pelvis [46,47,48,49] (Table 1). Notably, only one (R-Universal, Rossum Robot) of the 11 systems was specifically designed for the automatic reduction of pelvic fractures. Zhao et al. firstly reported this intelligent robot-assisted fracture reduction (RAFR) system [50, 51]. The RAFR system adopts the mirror symmetry principle and uses 3D CT data to reconstruct the pelvic model and determine the target reduction position based on the intact hemipelvis [52]. The unique advantages of the RAFR system are to allow programming of the optimal reduction path, automatically moving the fractured fragments following the planned path, and ultimately achieving precise reduction. The results from three clinical studies support the superior reduction quality using the system.

Table 1 List of orthopedic robotic systems available in the market

A case series study of 22 patients with unstable pelvic fractures has demonstrated that the RAFR system achieved 95.5% excellent and good quality of reduction with a mean residual displacement of 4.61 ± 3.29 mm [53]. A retrospective study of 49 patients revealed that the RAFR system resulted in 93% (38/41) excellent and good quality of reduction for posterior pelvic ring fractures and 100% (8/8) for anterior pelvic ring fractures [54]. A recent case series study found a residual displacement of 6.65 ± 3.59 mm and an excellent and good quality of reduction of 85% in 20 patients with type B or C closed pelvic fractures [55]. No postoperative complications were reported in any of these clinical studies. However, despite the promising results, these clinical studies were retrospective with small sample sizes and lacked a control group. In addition, the functional recovery outcomes of the patients were not presented. Thus, large comparative studies or randomized controlled trials with long-term follow-up data are required to further verify the clinical performance and safety of this reduction system.

The automatic reduction feature considerably relieves the physical and mental burden on the surgeon during the operation and further reduces the risk of radiation exposure. Wu et al. showed that when the RAFR system was used in the operation, the fluoroscopy frequency was 29.5 times [55], which is less than that from nonautomatic reduction procedure (43 times; reported by Li et al.) [45]. In addition, the automatic reduction feature also empowers greater flexibility in the reduction process compared with reduction frames. Due to their bulky structure, reduction frames cannot support fine-tuning of the reduction, which is particularly critical for the reduction of multidimensional displacement. The automatic reduction function of the RAFR system enables smooth and precise movement of the robotic arm following a preplanned optimal reduction path, which can maximally avoid damage to the soft tissue surrounding the fracture sites and thus reduce complications. Postoperative complications were not observed in the three clinical studies on this system [53,54,55]. One limitation of the RAFR system is that the maximum load of the robotic arm of the RAFR system is set to 160 N, which is lower than the force applied by the surgeon’s bare hand. Therefore, manually assisted reduction is still required when encountering bony obstruction exceeding the maximum load and dealing with fractures requiring a larger reduction force such as old fractures.

Future perspective

The pelvic fracture reduction technique has undergone tremendous evolution from open reduction to robot-assisted automatic reduction. The features, reduction quality, advantages, and shortcomings of each reduction technique mentioned in this review are summarized in Table 2. Although the reduction technique progress substantially, an unanswered question remains: what is the solution for bilateral pelvic fractures? All current advanced reduction techniques follow the mirror symmetry principle, which determines the target anatomic reduction position of the injured hemipelvis based on the geometry of the intact hemipelvis. Thus, an optimal treatment for bilateral pelvic fractures, which account for 18.3% of all unstable pelvic fractures, is lacking [56]. Moreover, even for unilateral pelvic fractures, the mirror symmetry reconstruction method might not always be effective because the patient may have spatial asymmetry in the pelvis [57]. One plausible solution for bilateral pelvic fractures or unilateral fractures with pelvic asymmetry appears to rely on machine learning and artificial intelligence technology to calculate the ideal target anatomic reduction position, which is based on a large amount of human pelvic geometry data. Ead et al. proposed establishing 3D models of the average shape of male and female pelvises and using them to reconstruct the target reduction position for bilaterally fractured pelvises [58]. Thus, the future development of pelvic reduction techniques should involve intelligent reduction, which builds personalized 3D pelvic models based on big data on pelvic geometry, age, sex, and other relevant aspects. Although robotic and navigation technologies, especially 3D real-time navigation and automatic reduction technologies, have revolutionized the reduction techniques for pelvic fractures, the adoption of these advanced technologies in clinical practice is low. In a recent international survey investigating standard practice in the treatment of unstable pelvic ring injuries, 65.4% of the respondents stated that they never used navigation techniques and 19.5% reported seldom using them [12]. One possible reason for the poor adoption of navigation and robotic technologies is the challenging learning curve of these advanced technologies. Therefore, providing systematic training on navigation and robotic systems to orthopedic surgeons should encourage the adoption of these advanced technologies and benefit healthcare professionals and patients.

Table 2 Evolution of the reduction technique for unstable pelvic fractures

Conclusion

In recent decades, pelvic fracture reduction techniques have evolved from open reduction to closed reduction, navigation-assisted closed reduction, and robot-assisted automatic closed reduction. Currently, most unstable pelvic ring fractures can be safely and effectively treated using a minimally invasive approach. Navigation and robot-assisted automatic pelvic fracture reduction remains in the preliminary stages, and robust clinical evidence is needed to further verify the clinical performance of these techniques. Systematic operational training on navigation and robotic systems is expected to promote the adoption of the most recent pelvic fracture reduction techniques. Furthermore, interdisciplinary inventions, such as artificial intelligence, will continuously drive the development of bone fracture reduction techniques, consequently improving patient clinical outcomes.

This narrative review offers significant value by aiding orthopedic researchers in understanding the evolution of reduction techniques for unstable pelvic fractures. However, this review has some limitations. Firstly, when assessing the safety and effectiveness of open and closed reduction techniques for pelvic fractures, we included retrospective or prospective cohort studies with a relatively large sample size. We did not find randomized controlled trials to conduct a pooled analysis of the data. Second, publications available for analyzing the safety and effectiveness of navigation-assisted closed reduction and robot-assisted closed reduction are sparse because these new techniques are still in their preliminary stages. In the future, robust evidence is needed to support the superiority of the new reduction techniques over traditional ones.