Minimally Invasive 360° Fusion Using a Combination of INFIX and Minimally Invasive Spinopelvic Fixation by Intraoperative Computed Tomography Navigation for Unstable Pelvic Ring Fracture: A Technical Note

Abstract

Objective

Fluoroscopy is often used in the surgery of unstable pelvic ring fractures, and improved safety in implant placement is an issue. An anterior subcutaneous pelvic fixator (INFIX) combined with a percutaneous screw has been reported to be a minimally invasive and effective surgical technique for unstable pelvic ring injuries. However, although percutaneous screw fixation is minimally invasive, its indications for fracture fixation and fractures with large fragment displacements in the vertical plane remain controversial. Therefore, this technical note aims to describe a new technique for unstable pelvic ring fractures.

Methods

We describe a 360° fusion of the pelvic ring to treat unstable pelvic ring fractures, including vertical shear pelvic ring fractures, using an intraoperative CT navigation system. Seven patients were treated with 360° fusion for type C pelvic ring fractures. In surgery, after reducing the fracture with external fixation, intraoperative CT navigation is used to perform a 360° fusion with INFIX and minimally invasive surgical spinopelvic fixation (MIS‐SPF). We will introduce a typical case and explain the procedure.

Results

A 360° fixation was performed, and no perioperative complications were noted. The mean blood loss was 253.2 ± 141.0 mL, and the mean operative time was 224.3 ± 67.4 min. In a typical case, bone union was obtained 1 year after surgery, and we removed all implants.

Conclusions

MIS‐SPF has a strong fixation force and helps reduce fractures' horizontal and vertical planes. In addition, 360° fusion with intraoperative CT navigation may help treat unstable pelvic ring fractures.

Fixation of unstable pelvic ring fractures and surgical methods for fractures with large fragment displacement in the vertical plane remains controversial. We describe the new techniques of an unstable pelvic ring fracture by 360° fusion with INFIX and minimally invasive surgery (MIS)‐SPF using intraoperative CT navigation.

Introduction

An unstable pelvic ring fracture is a serious, potentially life‐threatening injury that often requires internal fixation of the pelvis. Notably, AO/orthopaedic trauma association (AO/OTA) type C pelvic ring fractures, which are severe and unstable, are often accompanied by a rupture of the posterior ligaments, ¹ and vertical displacement (VD) may be present. These vertical shear pelvic fractures are unstable injuries caused by complete rupture of the anterior and posterior pelvic rings. Traditional unstable pelvic ring fixation methods include open reduction and internal fixation (ORIF). ² Various fixation techniques have been reported for ORIF. Each surgical method used to treat these injuries, including iliosacral screws (ISS) or transiliac–transsacral (TITS) screws, spinopelvic fixation (SPF), and transiliac plate fixation, has advantages and disadvantages. The surgical incision for traditional ORIF is highly invasive due to the extensive skin incision. In unstable pelvic ring injuries, anterior plating fixation alone may not reduce the posterior injury. The additional fixation of the posterior lesion is recommended, especially for vertical shear injuries. However, compared with patients undergoing other procedures, patients with ORIF for unstable pelvic ring fracture often experience more operative trauma, postoperative complications, and longer rehabilitation time. Thus, recently, the usefulness of a minimally invasive surgery (MIS) using intraoperative CT navigation has been reported. ³ , ⁴ , ⁵ , ⁶

An important aspect of posterior pelvic ring injury repair is ensuring sufficient stability to balance vertical and horizontal stress. Therefore, insufficient fixation leads to poor outcomes. ⁷ Previous papers have shown that simultaneous fixation of the anterior and posterior pelvic rings can offer adequate biomechanical stability, satisfactory healing, and functional recovery. ⁸ , ⁹ Thus, anterior and posterior fixation is recommended for treating unstable pelvic ring fractures. Commonly used methods for anterior fixation include plating, percutaneous screws, and external fixators. However, anterior plating is cumbersome and technically difficult in vertical shear, lateral compression injuries, and injuries due to a combined mechanism that usually results in complex fracture patterns of an anterior ring. In addition, anterior plating increases extensive exposure, prolongs the operative time, and is prone to complications.

To address these issues, an anterior subcutaneous pelvic fixator (INFIX) using spinal implants for pelvic ring fractures has been reported, which reduces intraoperative time and blood loss compared with conventional open surgery. ¹⁰

Moreover, MIS‐SPF procedures using percutaneous pedicle screws (PPS) have also been reported for posterior procedures, and their usefulness is recognized. ¹¹ , ¹² However, it is sometimes technically challenging to perform anteroposterior fixation for unstable pelvic ring fractures using only fluoroscopy. Therefore, we have performed a 360° fusion procedure using INFIX and MIS‐SPF with intraoperative computed tomography (CT) navigation for unstable pelvic ring fractures. The purpose of this study is to describe the surgical method for 360° fusion for unstable pelvic ring fractures. In this technical note, we describe a 360° fusion of the pelvic ring to treat unstable pelvic ring fractures, including vertical shear pelvic ring fractures, using an intraoperative CT navigation system.

Methods

Ethics Approval

The study protocol was reviewed and approved by the Committee on Ethics, the Institutional Review Board of Tokai University School of Medicine, and the Profit Reciprocity Committee (22R‐141). Because this study was a technical note, the requirement for informed consent was waived.

Radiological Evaluation and Surgical Technique

Fracture asymmetry (pelvic deformity index [PDI]) was measured using three‐dimensional (3D) CT, following the cross‐measurement method first described by Keshishyan et al. ¹³ and later modified by Lefaivre et al. ¹⁴ Furthermore, measurements of VD and pubic symphyseal width (PSW) were also carried out according to Lefaivre et al. ¹⁴ and Vaidya et al. ¹⁵ These measurements were performed preoperatively and postoperatively (Figure 1).

Fig. 1.

Measurement of the pelvic deformity index (PDI), vertical displacement (VD), and pubic symphyseal width (PSW) using 3D CT reconstruction. VD was measured from the top of the iliac crests, from a line perpendicular to the L5 reference line. X or Y is the diagonal length from the inferior sacroiliac joint (iliac side) to the inferior aspect of the teardrop. PDI = absolute (X − Y)/(X + Y). PSW was the largest width of the symphysis pubis.

Typical Case Patient History before Surgery

A 48‐year‐old man sustained fractures in a traffic accident, including a C1.3 pelvic fracture based on the AO/OTA classification system and type II left sacral fracture based on the Denis classification system, that is, vertical shear pelvic fractures (VD, 22.8 mm) and pubic symphysis dissociation (PSW, 20.6 mm). In addition, right ischium and pubis fractures were also observed. His other injuries included multiple rib fractures, hemopneumothorax, and ankle fractures. His preoperative X‐ray and 3D CT are shown in Fig. 2. The PDI was 0.0459, and no neurological abnormalities were noted. Temporary fixation was performed by external wound fixation on the day of injury.

Fig. 2.

Preoperative plain radiograph (A) and 3D CT reconstruction (B) of pelvic ring fracture indicated a type C1.3 fracture with Denis II fracture.

The INFIX Approach Using Intraoperative CT Navigation

In internal fixation surgery, the patient is initially operated on for internal fixation in the supine position on the operating carbon table (OSI Modular Table System; Jackson Table; Mizuho, Union City, CA, USA) under general anesthesia. After proper disinfection and draping, surgery begins. Once initiated, the external fixation is reassembled under fluoroscopy, and the fracture is reduced as much as possible. We then fix the navigation reference frame to the iliac crest. The intraoperative CT (O‐arm2® Imaging System; Medtronic, Dublin, Ireland) is then positioned, and 3D‐reconstructed images are acquired and transmitted to the StealthStation Surgical Navigation System (S7; Medtronic Sofamor Danek, Minneapolis, MN, USA). We use the navigation to identify the approach point without requiring fluoroscopy. A 2–3‐cm vertical incision is centered on the anterior inferior iliac spine, and the Sartorius and tensor fasciae latae are carefully spaced, taking great care to protect the lateral femoral cutaneous nerve.

The Navigate Fast Bar Stealth‐Midas System (Medtronic Sofamor Danek, Minneapolis, MN, USA) and navigated pedicle probe are used to drill screw holes and insert CD Horizon® Ballast screws (Medtronic Sofamor Danek, Minneapolis, MN, USA), which are polyaxial pedicle screws. Navigation is also used to size the screws according to the patient's physique. However, we mainly use multiaxial pedicle screws with a diameter of 8.5 mm and a length of 80 mm, with at least 60 mm of the screw being intraosseous and about 20 mm outside the bone. The screw head is placed to rest above the deep fascia to avoid compression of the femoral nerve and inguinal ligament (Fig. 3). After screw insertion, we use fluoroscopy to check for misplacement of the screws. Fluoroscopy is directed toward the oblique exit of the obturator to view the resulting teardrop (corridor for screw insertion) and to verify the correct screw insertion (Fig. 4).

Fig. 3.

Anterior screw insertion method using intraoperative CT navigation. (A) Navigated pedicle probe and (B) navigated CD Horizon® Ballast screw.

Fig. 4.

Intraoperative obturator outlet fluoroscopic view showing teardrop for the anterior screw.

Next, rod insertion is performed. The insertion position of the rod is set to pass through the “bikini line.” This area is especially prominent in obese people but is found in most people. We can check this by flexing both hip joints, that is, the upper edge of this area is usually a fold or line marking the path of the subcutaneous rod. Because the area is the same whether the patient sits or stands, we can place the rod here regardless of the patient's position. We measure the length of the rod we need and bend the rod to fit the contour of the anterior pelvis. We then insert a 5.5‐mm‐diameter rod from one side and guide it to the subcutaneous surface toward the other side. As the rod approaches the contralateral screw, it is guided to the contralateral pedicle screw using rod‐holding forceps. Once the rod is in place, the set screw is secured to the screw, and the screw head is fixed to both sides. The reduction position, including the anterior elements, is confirmed by fluoroscopy, and the external fixation is removed (Fig. 5).

Fig. 5.

After INFIX with external fixation. Intraoperative x‐rays before (A) and after (B) external fixation indicate posterior vertical dislocation (arrow).

We present a video of the INFIX technique with intraoperative CT navigation (Additional file 1: Video S1).

MIS‐SPF Technique

After INFIX, and the patient is placed in the prone position. The reference frame is placed on the spinous process, and intraoperative CT is retaken. The imaging range (field of view) is widened so that the entire pelvis can be seen, and information is transmitted to the navigation workstation. The implant is a PPS and a Ballast iliac screw with the CD Horizon SOLERA Voyager System (Medtronic, Dublin, Ireland).

After registering all instruments dedicated to Stealth navigation, the lumbar PPS is inserted using real‐time navigation. When inserting the PPS, we do not insert the L5 screw on the side of the vertical dislocation, as it interferes with the reduction maneuver. Instead, the connector is placed between the rods and is used to distract the screws. An entry point is created using the Stealth‐Midas System, and it is possible to determine the screw size intraoperatively by displaying the virtual tip. After inserting the PPS into the lumbar spine, the left and right iliac screws are inserted. A 5‐cm incision is made along the medial border of the posterior superior iliac spine (PSIS). We then proceed with the resection of the iliac bone, exposing the superior surface of the PSIS. Bone resection is performed to ensure that there is no protrusion of the heads of the screws to prevent postoperative irritation and skin necrosis. Then, using navigational techniques, insert two iliac screws bilaterally as equidistant as possible. Iliac screws with dimensions that do not allow for penetration of cortical bone are selected. Where possible, we use large iliac screws, that is, >7 mm in diameter with a length ≥ 60 mm. The iliac screws are set lower than the top of the PSIS.

Next, the offset connector attached to the iliac screw through the rod from the PPS direction of the cranial side is connected to the rod (Fig. 6). Vertical reduction of the fracture is then advanced by placing the gripper on the rod and performing the distraction between the offset connector and the gripper. After vertical reduction, the reduction is performed by applying compression in the lateral direction. The distance between the screws on the left and right sides is measured, and 5.5‐mm‐diameter rods are cut to an appropriate length based on the distance. Since the sacrum bulges dorsally and the iliac screws on both sides are inserted laterally, bending the rods into a W‐shape makes it easier to place them under the muscle layer. By connecting the rod to the lower pairs of screws on both sides, the left and right iliac screws are connected. Finally, closure is carried out layer by layer by covering the head of each screw with fascia to prevent discomfort as much as possible related to the protuberance of the screw head.

Fig. 6.

Minimally invasive surgical spinopelvic fixation (MIS‐SPF) technique for unstable pelvic ring fractures with vertical shear. Navigation‐assisted (A) percutaneous pedicle screws (PPS) insertion and (B) rod insertion; (C) distraction technique between the gripper and offset connector; (D) surgical field after distraction; (E) fluoroscopic image after distraction (arrow); (F) fluoroscopic image after lateral compression (arrow), and connection of the rod to the lower pairs of screws on both sides. From (E) to (F): dislocation of the sacroiliac joint has been reduced due to the lateral compression force applied to the iliac screw.

We present a video about the MIS‐SPF technique using intraoperative CT navigation (Additional file 2: Video S2).

Although the patient's starting time for walking varied depending on the presence or absence of other comorbid injuries, we allowed them to use a wheelchair and walk during the early postoperative period, including, if pain allowed, the day after the operation. A postoperative CT scan was always taken immediately to ensure all implants were in the correct position and the reduction was good.

Typical Case Patient History after Surgery

In our 48‐year‐old patient, 360° fusion was performed 4 days after the patient's accident. Anterior surgery with INFIX had an operative time of 149 min and an estimated blood loss of 146 mL. The posterior MIS‐SPF had an operative time of 120 min and an estimated blood loss of 301 mL. No perioperative complications were noted. The patient was transferred to another hospital 38 days after the operation (Fig. 7). Postoperative 3D CT improved VD to 2.2 mm, PSW to 8.7 mm, and PDI to 0.0250. Six months after surgery, the anterior implant was removed. One year after the operation, bone union was obtained, and the posterior implant was also removed (Fig. 8). The Majeed score ¹⁶ at the time of posterior implant removal was 73 points (Pain, 25; Work, 0; Sitting, 10; Sexual intercourse, Four; Walking aids, 12; Unaided gait, 12; Walking distance, 10). There were no complaints concerning the pelvic ring fracture, and the patient almost returned to preinjury activity levels.

Fig. 7.

The postoperative (A) pelvic anteroposterior (AP) view and (B) 3D CT reconstruction of the pelvic ring fracture confirmed the reduction of the vertical shear dislocation and pubic symphysis dissociation of the fracture. (C) There is no deviation of each anterior (dashed arrow) and posterior screw (solid arrow) in the obturator outlet view by 3D CT reconstruction.

Fig. 8.

Postoperative plain radiograph 1 year after surgery. (A) Pelvic anteroposterior (AP) view; (B) pelvic inlet view; and (C) pelvic outlet view. Postoperative plain radiograph 1 year after surgery showed bone union, and all implants were removed.

We present a walking video after implant removal (Additional file 3: Video S3).

Results

The Patients Demographics and Surgical Data

The results of the surgeries of the seven patients (four men, three women; age 39.9 ± 18.3 years) using 360° fusion (INFIX + MIS‐SPF) are summarized in Table 1. The AO/OTA classification of fracture type was 61‐C1.1 in one patient, C1.2 in two, and C1.3 in four. Seven patients had pubic rami fractures, and two had PSW. The mean injury severity score was 19.0 ± 9.9 (median, 22). Traffic accidents were the leading cause of injury (five patients). The mean elapsed time from traumatic event to surgery was 4.1 days. The mean blood loss was 253.2 ± 141.0 mL, and the mean operative time was 224.3 ± 67.4 min. Because two patients had surgery for femoral fractures along with pelvic ring fractures, the results also include operative time and blood loss. The operative time and blood loss, excluding the treatment of comorbid fractures, were 196.2 ± 53.3 min and 277.6 ± 142.8 mL, respectively. This operating time also includes the time for patients' position change, the time for intraoperative CT navigation, and the time for external fixation.

TABLE 1.

Patient demographic data for 360° fusion (anterior subcutaneous pelvic fixator [INFIX] + Minimally invasive surgical spinopelvic fixation [MIS‐SPF])

Characteristic		Data
No. of patients		7
Age (years)		39.9 (18.3)
Sex (male/female)		4/3
ISS		19.0 (9.9)
Mechanism of injury	Traffic injury	5
	Fall from height	2
Pelvic fracture type (AO/OTA classification)	C1.1	1
	C1.2	2
	C1.3	4
Anterior pelvic ring injury	Pubic rami fracture	7
	Pubic symphysis dissociation	2
Associated injury	Brain injury	1
	Rib fracture	4
	Limb fracture	5
	Abdominal injury	3
Time from injury to surgery (days)		4.1 (3.8)
Operation time (min)		224.3 (67.4)
Blood loss (mL)		253.2 (141.0)
VD (mm)	Pre‐operation	8.3 (8.7)
	Post‐operation	4.6 (9.6)
PSW (mm)	Pre‐operation	9.2 (13.7)
	Post‐operation	2.8 (2.8)
PDI	Pre‐operation	0.0454 (0.0215)
	Post‐operation	0.0336 (0.0256)

Note: Data are presented as mean (SD)

Abbreviations: AO/OTA, AO/orthopaedic trauma association; ISS, injury severity score; HD, horizontal displacements; PDI, pelvic deformity index; VD; vertical displacements.

Pre‐ and postoperative 3D CT showed a mean reduction in VD from 8.3 to 4.6 mm and PSW from 9.2 to 2.8 mm. The PDI improved from 0.0454 to 0.0336 before and after surgery.

Discussion

This technical note described a 360° fusion using an intraoperative CT navigation system for seven patients with unstable pelvic ring fractures, including vertical shear pelvic ring fractures. Anterior fixation combined with posterior fixation is recommended to treat unstable pelvic ring fractures. However, conventional anterior fixation is invasive for patients because it requires large skin incisions. Hence, the INFIX technique was developed; this is a minimally invasive internal fixation procedure for the pelvic ring using spinal implants. ¹⁰ Compared with other fixation types, INFIX has been reported to be less invasive to soft tissue and has fewer reported wound infections. Therefore, anteroposterior 360° fusion using INFIX and percutaneous screws such as ISS or TITS can also be applied to unstable pelvic ring fractures. ⁷

The 360° fusion procedure at our hospital is usually performed from anterior to posterior. The advantage of starting anteriorly is that intraoperative external fixation can be used, and we can fix the pelvic ring by maintaining the reduction position while performing external fixation. Although most INFIX surgeries reported to date have been performed under fluoroscopy, ¹⁵ , ¹⁷ we previously noted that this technique could be easily performed using intraoperative CT navigation. ¹⁸

In posterior procedures, the application of ISS and TITS screws is widely accepted for treating posterior pelvic ring injuries. ¹⁹ , ²⁰ However, this screw fixation reduces the transverse plane but not the vertical plane of dislocation. Moreover, the optimal corridors of ISS and TITS screws are narrow, and the fluoroscopy procedure requires a high degree of technical skill. Therefore, insertion of the screw in cases with severe vertical or horizontal dislocation is difficult. It has been suggested that a statistically significant correlation exists between vertical shear‐type fractures and the frequency of sexual dysfunctions. ²¹ Thus, reduction in the vertical plane is particularly important functionally. ²² For example, among unstable pelvic ring fractures, pelvic ring fractures with a vertical dislocation of ≥10 mm are considered to cause lumbosacral plexus neuropathy. ²³ A previous paper demonstrated that incomplete fracture reduction of acetabular fractures correlated with a worse outcome because of secondary spinopelvic imbalance, with posture and gait impairment. ²⁴ Furthermore, in the case of hemipelvis elevation or elevation–rotation, asymmetry in acetabular orientation or indirect leg length difference is functionally not exceptionally well tolerated. Thus, techniques such as vertical reduction by intraoperative traction or a reduction operation by SPF using a spinal instrument have been reported. ²⁵ , ²⁶ SPF provides vertical reduction, stabilizing the fracture in multiple planes and allowing an early return to weight‐bearing. However, one of the drawbacks of conventional open SPF is the high infection rate, with the surgical site infection rate reported to be 16%. ²⁷

MIS‐SPF using PPS can help to reduce the infection rate and shorten the average surgical time. ¹¹ This is particularly important in treating hemodynamically unstable polytrauma patients, but it may also be useful in treating more fragile elderly patients. Thus, 360° fusion using INFIX + MIS‐SPF is suitable for unstable pelvic ring fractures with severe vertical or lateral dislocations. A similar procedure using INFIX and crab‐shaped fixation has been reported. ⁸ However, our technique uses intraoperative CT navigation, which enables 360° fusion in a minimally invasive manner and may reduce the surgeon's stress. On the other hand, the disadvantage of this procedure is the need for CT navigation during surgery, which poses the problem of equipment introduction costs and high investment. Furthermore, it is an evaluation of the accuracy of navigation. ²⁸ Further verification of the cost‐effectiveness of this procedure may be necessary. Regarding the accuracy of navigation, it is necessary to check fluoroscopy for discomfort during surgery. Another issue that deserves more attention is radiation dosage. The radiation dosage for intraoperative CT is typically much higher than conventional fluoroscopy. ²⁹ However, the previous paper demonstrated that total radiation exposure for intraoperative CT‐assisted posterior spinal fusion throughout treatment is not significantly different from fluoroscopy. ³⁰ This may be related to the times of intraoperative fluoroscopy, duration of use, and the rate of pre‐and postoperative CT scans. Screw insertion by fluoroscopy requires more time than intraoperative CT navigation techniques. In contrast, there are lower pre‐ and postoperative CT scans with the assistance of the intraoperative CT navigation technique. Of equal concern is the proportion of total radiation dose applied to surgeons and operating room staff during fluoroscopy. However, intraoperative CT navigation procedures can limit radiation exposure for surgeons and operating room staff. Additionally, the surgeon is closest to the radiation source during conventional screw insertion, which is not the case with intraoperative CT.

Strength and Limitations

Our 360° fusion by intraoperative CT may be considered less invasive for unstable pelvic ring fractures. Some limitations, such as the short follow‐up and the small number of patients included, should be noted. Unfortunately, this is a technical note paper, and a longer follow‐up of more patients or a comparison with the other techniques is needed to confirm that this technique is beneficial. In addition, in future work, it is necessary to examine patients to determine the possible degree of correction and obtain a detailed clinical evaluation. A new score that assesses psychological aspects is considered necessary, especially for evaluating the outcome of unstable pelvic fractures. ³¹

Conclusion

In conclusion, 360° fusion using intraoperative CT navigation is useful as a safe surgical technique even for severe unstable pelvic ring fractures. It provides strong fixation and reduces fracture‐dislocation. This is particularly advantageous for vertical shear pelvic ring fractures.

Author Contributions

All authors have read and approved the manuscript. Akihiko Hiyama and Taku Ukai: study design, data interpretation, surgical procedures, writing of manuscript and final approval. Shota Ogasawara: data collection, data interpretation and surgical procedures. Tatsumi Tanaka: data collection and final approval. Masahiko Watanabe: data interpretation and final approval.

Supporting information

VIDEO S1: Supporting Information.

VIDEO S2: Supporting Information.

VIDEO S3: Supporting Information.