Efficacy and safety of conventional biplanar and triangulation method for sacroiliac screw placement in the treatment of unstable posterior pelvic ring fractures: A real-world retrospective cohort study

Abstract

Purpose

The fixation method commonly employed worldwide for treating unstable fractures of the posterior pelvic ring is the percutaneous iliosacral screw technique. However, prolonged operation time and frequent fluoroscopies result in surgical risks. This study aimed to investigate whether a new triangulation method could reduce operative and fluoroscopy times and increase the accuracy of screw placement.

Methods

This study is a real-world retrospective cohort analysis that examined a patient cohort who underwent percutaneous iliosacral screw fixation between January 1, 2019 and December 31, 2022. Inclusion criteria were patients (1) diagnosed with posterior pelvic ring instability who underwent pelvic fracture closed reduction and percutaneous S1 transverse-penetrating iliosacral screw placement and (2) aged >18 years. Exclusion criteria were: (1) combined proximal femoral fractures, (2) severe soft tissue injury in the surgical area, (3) incomplete imaging data, and (4) declining to provide written informed consent by the patient. The patients were divided into 2 groups according to the screw insertion method: conventional and triangulation methods. Screw placement and fluoroscopy times recorded by the C-arm were compared between the 2 methods. The accuracy of screw placement was evaluated by Smith grading on postoperative CT. Normality tests were conducted to assess the distribution of the quantitative variables and the Chi-square test was used to compare the qualitative variables.

Results

The study included a total of 94 patients diagnosed with posterior pelvic ring instability, who underwent percutaneous iliosacral screw placement. The patients were divided into 2 groups: 46 patients treated with the conventional surgical method and 48 patients received the triangulation method. The operation time (61.13±9.69 vs. 35.77±6.27) min and fluoroscopy frequency times (52.15±9.29 vs. 24.40±4.04) of the triangulation method were significantly reduced (p<0.001).

Conclusions

The use of a triangular positioning technique for the surface positioning of percutaneous iliosacral screws could reduce the operative time and fluoroscopy frequency. And the screw placement accuracy using this new method was comparable to that using other conventional methods.

1. Introduction

High rates of mortality and disability are commonly observed in individuals with unstable fractures of the posterior pelvic ring.^1,2 The sequelae of treatment failure include intestinal and bladder incontinence, sexual dysfunction, pain, and movement disorders.^3,4 Iliosacral screws are frequently used for stabilizing posterior pelvic ring injuries.^5,6 They offer several benefits such as reduced surgical duration, minimal invasiveness, decreased bleeding, low infection risk, and dependable fixation.7, 8, 9 However, achieving precise placement remains a challenge with reported rates of iliosacral screw misplacement under C-arm guidance ranging between 2% and 24%.10, 11, 12 Successful placement necessitates a comprehensive comprehension of the lumbosacral pelvic region's anatomy and expertise in operating the C-arm. Inexperienced surgeons encounter extended operative and fluoroscopy durations, which heighten surgical safety risks and impede the advancement and acceptance of this approach.

The conventional positioning method for percutaneous iliosacral screws is the dual-plane fluoroscopy-guided method,¹³ by which the surgeon observes the relationship between the guide pin and safe channel under C-arm fluoroscopy of the pelvis. The position of the screw entry point was determined by lateral pelvic radiographs, which often necessitated multiple adjustments of the C-arm position and consumed a significant amount of time (Fig. 1A). At present, the primary emphasis in studies regarding iliosacral screw placement has been directed toward positioning screws within the sacrum.14, 15, 16 However, the position of guide pins on the body surface should not be ignored. The iliosacral screw guide pin is passed through the gluteus maximus muscle during insertion. If placed on the surface of the body, it becomes displaced, making adjustments to the screw or guide pin located beneath the gluteus maximus muscle challenging. Surgeons often need to perform multiple fluoroscopies to adequately adjust the guide pins, which increases the risk of radiation exposure. Moreover, repeated adjustment of the guide pin in the soft tissue could increase the risk of bleeding and infection.³ Recently, there has been a rise in the use of advanced techniques for positioning, including the implementation of robot-assisted positioning and O-arm navigation.^17,18 However, the timely application of this method is often not available to patients with acute and severe diseases. Further studies are necessary to improve the accuracy of the free-hand placement of iliosacral screws. Moreover, in some hospitals, affording the cost of this advanced equipment is difficult (Fig. 2).

Fig. 1.

Comparison between conventional and triangulation methods. (A) The conventional technique necessitates the use of a fluoroscopic lateral view of the pelvis to identify a secure pathway through the sacrum and subsequently ascertain the precise location for making an incision on the skin. (B) The triangulation method involves drawing an equilateral triangle that connects the anterior superior iliac spine with the greater trochanter of the femur to determine the precise location for the surgical incision. The femoral greater trochanter choice for the central point. (C) An example of a triangulation method in action.

Fig. 2.

Flow chart of study inclusion.

Our prior investigation on a 3-dimensional model of pelvic CT reconstruction in normal individuals revealed that the skin entry point of the percutaneous iliosacral screw had a positional relationship with the anterior superior iliac spine and greater trochanter from an entry point on the skin (Fig. 1B).¹⁹ There exists a triangular relationship that is equilateral, which defines the S1 transverse iliosacral screw, anterior iliac spine on the same side, and greater trochanter (Fig. 1C). In this study, we investigated whether the triangulation method could reduce the number of fluoroscopies required and operating time, increase screw placement accuracy, and make it a feasible option in clinical practice compared with the conventional dual-plane adjustment technique.

2. Methods

2.1. Study design

This study was a retrospective, single-center investigation conducted from January 1, 2019 to December 31, 2022 at the Trauma Center of Qilu Hospital of Shandong University. This research study followed the ethical guidelines specified in the 1964 Declaration of Helsinki. Approval of the study design was granted by the Medical Ethics Committee of the Hospital.

2.2. Patient selection

The inclusion criteria were as follows: patients (1) diagnosed with posterior pelvic ring instability who underwent pelvic fracture closed reduction and percutaneous S1 transverse-penetrating iliosacral screw placement and (2) aged >18 years. The exclusion criteria were as follows: (1) combined proximal femoral fractures, (2) severe soft tissue injury in the surgical area, (3) incomplete imaging data, and (4) declining to provide written informed consent by the patient. The patients were divided into 2 groups according to the screw insertion method: the conventional method group and the triangulation method group. Both groups underwent surgery by the same surgical team.

2.3. Resuscitation and perioperative protocol

The patients were transferred to the emergency department in our hospital directly from the trauma scene or primary care. The advanced trauma life support resuscitation protocol was followed in the emergency department. Thereafter, the patients were transferred to the emergency surgical general ward or intensive care unit as needed. Pelvic fracture fixation was performed immediately after hemodynamic stabilization. Imaging studies included radiography (anteroposterior, entrance, and exit views) and whole-body CT to assess the degree of injury and detect potential fractures. Subsequently, individual surgical plans were established according to associated injuries and fractures. Similar imaging examinations were performed postoperatively to evaluate the quality of pelvic ring reduction and precision of implant position.

2.4. Surgical technique

Under general anesthesia, the patient was placed in the supine position and an iliosacral screw was inserted. Reduction was performed according to the type of pelvic injury before screw insertion. After satisfactory reduction, a pelvic external fixator, infix, pubic symphysis plate, LC2 screw, or other methods can be used to stabilize the anterior pelvic ring. The conventional biplanar positioning technique was used for cases undergoing surgery from January 1, 2019 to June 30, 2021. The surgical procedures were as follows: the C-arm was adjusted to obtain a lateral pelvic radiograph; the iliac cortical density line was adjusted to coincide well; the S1 safe channel was determined according to the lateral sacral image (Fig. 1A). A guide pin was placed in the soft tissue and pointed to the safety pass. After confirming the guide pin position, the cortical bone was broken. Images of the pelvic inlet and outlet views were used for confirming whether the positioning point and direction of the guide were pinpointed toward the safe channel of the iliosacral screw. During implantation, the C-arm was repeatedly adjusted to obtain pelvic inlet and outlet position films to monitor whether the guide pin was positioned in a safe channel.

The triangulation group included surgical cases from July 1, 2021 to December 31, 2022. Before the operation, the anterior superior iliac spine and greater trochanter of the femur were marked and the equilateral triangle of the iliosacral screw was drawn (Fig. 3A). The skin insertion point was determined preliminarily and was adjusted based on the patient's body type, sex, and other influencing factors. This method required fluoroscopy only at the inlet and outlet positions. After placing the screws, a lateral view of the sacrum was used to verify the position of the screws. A 7.3-mm half-threaded or 6.5-mm full-threaded hollow screw could be used as the target implant depending on whether compression was required (Fig. 3B). Image data of the C-arm were recorded and saved during percutaneous screw placement. The main difference between the triangulation and conventional methods is the positioning of the skin incision through the greater trochanter of the femur and anterior superior iliac spine, without the need for fluoroscopic lateral pelvic radiographs.

Fig. 3.

Surgical procedure of the triangulation method. (A) The surgical incision is located by triangulation before the operation. (B) Intraoperative fluoroscopic images to monitor the guide pin is positioned in the safe passage of the sacrum. (C) Postoperative CT images. (D) Postoperative X-ray films.

2.5. Postoperative measurement

As part of the standardized treatment protocol, all patients underwent thin-slice CT scans for pelvic fixation and serial radiography before discharge (Fig. 3C & D). The follow-up strategy comprised one radiographic examination in the first postoperative month, including the inlet, outlet, and lateral views of the pelvis, and imageological examinations every 2 months thereafter for at least 6 months. The follow-up included an investigation of whether the patients experienced sacroiliac pain and had bowel and bladder function, or motor function.

2.6. Data collection

We recorded the demographic data of each patient, including sex and age. The number of fluoroscopies was determined based on the actual number of C-arm recordings. The actual operative time was calculated based on the time of the first pelvic image recorded by the C-arm and the time of the last pelvic image after screw placement. Screw placement accuracy was scored using the Smith method, including anterior perforation, spinal canal or posterior perforation, superior or inferior perforation, and angulation scores. The patients were followed up according to their outpatient records.

2.7. Statistical analysis

Statistical analyses were performed using SPSS software (version 26.0; IBM Corp., Armonk, NY, USA). Normality tests were conducted to assess the distribution of the quantitative variables. The student t-test or the Mann–Whitney U test was used to compare quantitative variables based on the results of the normality test. The Chi-square test was used to compare the qualitative variables. Statistical significance was set at p < 0.05.

3. Results

3.1. Patient demographics

A total of 94 patients (54 male and 40 female individuals) with posterior pelvic ring instability were treated with percutaneous S1 transverse-penetrating iliosacral screw fixation (Table 1). Among them, 46 and 48 patients were treated with conventional surgical method and the triangulation method, respectively. There were no statistically significant differences in sex, age, or type of pelvic fracture.

Table 1.

Patient demographics.

Variables	Conventional surgical methods, n = 46	Triangulation method, n = 48	p value
Sex, n (male/female)	27/19	27/21	0.809
Age, mean ± SD (year)	41.70 ± 14.80	40.60 ± 13.90	0.720
BMI, mean ± SD (kg/m2)	23.97 ± 3.55	23.04 ± 3.46	0.211
AO type, n (%)			0.622
A	0 (0)	0 (0)
B	31 (67.39)	30 (62.50)
C	15 (32.61)	18 (37.50)
Denis classification, n (%)			0.120
I	22 (47.83)	19 (39.58)
II	15 (32.61)	16 (33.33)
III	5 (10.87)	2 (4.17)
Sacroiliac joint separation	4 (8.70)	11 (22.92)

SD: standard deviation; AO: adverse outcome; BMI: body mass index.

3.2. Screw placement

The triangulation group showed a significantly shorter operative time compared with the conventional surgery group. The mean duration of surgery was (61.13±9.69) min in the conventional surgery group, whereas it was only (35.77±6.27) min in the triangulation group. Additionally, there were averages of 24.40±4.04 and 52.15±9.29 fluoroscopies per screw in the triangulation and conventional surgery groups, respectively (p<0.001).

3.3. Smith score

The Smith score was used to evaluate iliosacral screw accuracy (Table 2). In the conventional surgery and triangulation groups, the average Smith scores were 0.61 and 0.46, respectively. No statistically significant disparities were found between the 2 groups.

Table 2.

Smith score of conventional method and triangulation method groups.

Variables	Conventional surgical methods, n = 46	Triangulation method, n = 48	p value
Anterior perforation			0.991
0 mm	36 (78.3)	38 (79.2)
<2 mm	9 (19.6)	9 (18.8)
2–4 mm	1 (2.1)	1 (2.0)
>4 mm	0 (0)	0 (0)
Canal or posterior perforation			0.877
0 mm	39 (84.8)	43 (89.6)
<2 mm	6 (13.0)	5 (10.4)
2–4 mm	1 (2.2)	0 (0)
>4 mm	0 (0)	0 (0)
Superior or inferior perforation			0.574
0 mm	38 (82.6)	46 (95.8)
<2 mm	8 (17.4)	2 (4.2)
2–4 mm	0 (0)	0 (0)
>4 mm	0 (0)	0 (0)
Angulation			0.749
<5°	45 (97.8)	44 (91.7)
5°–10°	1 (2.2)	4 (8.3)
11°–15°	0 (0)	0 (0)
Smith Score	0.61 ± 0.82	0.46 ± 0.73	0.356

Data presented as n (%) or mean ± SD. SD: standard deviation;

3.4. Complications

The patients were followed up for an average of 7 months. None of the patients experienced infection, bleeding, or iliosacral screw breakage. Five patients experienced sacroiliac pain (2 in the conventional surgery group and 3 in the triangulation group). After re-examination of the CT images to confirm fracture healing, the screw was removed, leading to the patient's sacroiliac pain disappearance. One patient still experienced plantar numbness and ankle joint movement disorder 3 months after the operation. The Smith score of 1 was considered to be related to the original fracture injury.

4. Discussion

This study aimed to assess the effectiveness and safety of the conventional biplanar and triangulation techniques in 94 patients who underwent percutaneous placement of the iliosacral screw. The findings indicated that compared with the conventional approach, using the triangulation method resulted in reduced operation time and decreased need for fluoroscopies. Regarding safety, no significant disparities were observed between the triangulation technique and conventional surgical approaches.

The technique of triangular positioning entails the use of anatomical reference points, e.g., the anterior superior iliac spine and greater trochanter of the femur, on the external surface of the body to ascertain the exact insertion site for a percutaneous transverse-penetrating screw at S1 in the iliosacral region. In our previous study, 182 healthy pelvises were collected. After modeling, Mimics software (Mimics25.0, Materialise N.V., Belgium) was used to simulate the placement of the S1 transverse-penetrating iliosacral screw; both ends of the screw were extended to intersect the skin to determine the entry point of the iliosacral screw. The measurements and modeling of the distances between the anterior superior iliac spine and the greater trochanter of the femur, as well as between the insertion point and both the ipsilateral anterior superior iliac spine and greater trochanter of the femur, were conducted in a 2-dimensional plane. Statistical analysis indicated that the majority of entry points (95%) were concentrated within a 12 mm range near the apex of an equilateral triangle. This triangle was formed by connecting the anterior superior iliac spine and the greater trochanter of the femur, with a preference toward the dorsal side at the head end. Various factors such as sex, body mass index, and angle of femoral external rotation had an impact on the precision of this modified approach. Compared with men, the positioning in women is more ventral. Furthermore, the positioning in individuals with overweight is more dorsal. Since the greater trochanter of the femur is connected to the pelvis through the hip joint, the rotational position of the femur is also an important factor affecting positioning accuracy. To minimize the effect of femoral rotation, the tip of the patient's foot was adjusted to a vertical position.

The posterior pelvic ring bears 60% of the load on the human body,⁸ for which firm fixation is required to stabilize it. The technique of placing the screw laterally to the sacroiliac joint for fixing sacral fractures, known as iliosacral screw placement, aims to stabilize the S1 vertebral body. This method of central fixation is biomechanically advantageous in promoting stability during internal fixation and facilitates earlier weight-bearing in these patients.²⁰ It additionally offers the benefits of reduced trauma, decreased blood loss during surgery, and minimized periosteal damage, all contributing positively to the recuperation process following the operation.¹⁵ The reliable fixation is achieved by the transverse iliosacral screw, which effectively penetrates 6 layers of cortical bone. However, in patients without safe passage through the S1 vertebra, only oblique screws could be selected. In patients who require oblique screw placement, the position of the transverse-penetrating screw placement can also be found on the body surface using the triangulation method and then adjusted to the ventral head end by referring to the position of the transverse screw placement through the deviation of the screw in the channel.

In actual operations, the difficulty of closed reduction in the posterior pelvic ring varies across patients. Therefore, we select the actual screw placement time rather than the operative time as a parameter in our study. The actual screw placement time is measured from the entrance position of the pelvis after closed reduction to the end of the lateral view of the pelvis after screw placement. Total intervention times are calculated from the time recorded by the C-arm images. Since patients with pelvic fractures often have additional fractures, other procedures may be necessary during the actual operation. For complex fractures that may be associated with soft tissue entrapment, closed reduction requires prolonged traction. Therefore, the actual implantation time is selected to reduce the confounding factors during surgery.

The conventional surgical methods pose several challenges. Regarding conventional surgery, the placement of the transverse sacroiliac screw skin incision is determined through fluoroscopic lateral view of the pelvis. Achieving an optimal lateral pelvic radiograph often requires significant time for adjusting the C-arm angle during the procedure. Additionally, owing to the need to traverse the gluteus maximus muscle during sacroiliac screw placement, there are limitations to adjusting the guide pin angle after crossing this muscle. Furthermore, multiple adjustments of the guide pin position can lead to unnecessary additional damage to soft tissues and increase the risk of infection.

Shortening screw placement time and reducing the fluoroscopy time can ensure the improved patient safety, reduce the risk of anesthesia adverse events, and reduce the radiation exposure among patients and doctors. In addition, the shortening of placement time and reduction in fluoroscopy time also indirectly reflect the reduction in the number of guide needle adjustments in the patient's body and thus can reduce soft tissue injury and the risk of infection. Currently, the use of orthopedic surgical robots or O-arm systems is a research hotspot directed at improving the accuracy of iliosacral screw placement, shortening the operation time, and reducing the number of fluoroscopies. Berger-Groch et al.¹¹ conducted a comparison between a conventional fluoroscopy technique and a 2-dimensional navigation procedure, revealing similar rates of positional errors. However, it was observed that the radiation dose associated with the conventional technique was twice as high as that of the 2-dimensional navigation procedure. Richter et al.²¹ discovered that the use of intraoperative CT resulted in a notable decrease in screw perforation incidents compared with conventional three-dimensional navigation techniques. The study by Florio et al.¹⁸ found that the use of an O-arm for iliosacral screw placement significantly reduced operative time and allowed the surgeon to completely avoid radiation exposure. However, these new technologies require a long learning curve and are expensive for patients.²⁰ Robot navigation technology is difficult and not widely used in intermediate and primary care hospitals due to its high operational costs and complex technical equipment requirements.²² The total cost must be considered, which makes performing the iliosacral screw technique difficult in secondary hospitals. Triangulation is a simple method based on surgical experience that improves positioning accuracy. It is easy to promote and the risk is small.

The triangulation method is employed to determine the precise location of the surgical skin incision using bone markers. However, it exhibits a significant bias in cases of obesity. Additionally, the presence of hematoma resulting from soft tissue injury within the surgical area is considered a contraindication to this approach. Moreover, reliance on the greater trochanter of the femur as a reference point for positioning poses challenges in patients with hip fractures.

This study has some limitations. First, the sample size of this study was small. Additionally, considering that the operator's increased proficiency may have influenced the reduction in operative time and fluoroscopy times is important. Our plans involve expanding the sample size and extending the follow-up period to further investigate both the advantages and potential contraindications associated with using the triangulation method for transverse placement of the first sacral iliosacral screw.

In conclusion, the implementation of the triangulation technique in this research for identifying the surface of percutaneous iliosacral screws led to reduced operative time and reliance on fluoroscopy. Nevertheless, no notable disparity was observed in terms of screw positioning precision compared with conventional approaches.

CRediT authorship contribution statement

Yu-Bo Zheng: Data curation, Formal analysis, Investigation, Methodology, Resources. Xing Han: Supervision, Validation. Xin Zhao: Resources, Supervision, Validation, Writing – original draft. Xi-Guang Sang: Funding acquisition, Investigation, Validation, Visualization, Writing – original draft, Writing – review & editing.

Ethical statement

Ethical approval was obtained from the Ethics Committee at Qilu Hospital of Shangdong University.

Funding

This work was supported by the National Key Research and Development Program of China (2019YFF0302303).

Declaration of competing interest

None.