Treatment of unstable spinopelvic fractures: outcome of three surgical techniques—a retrospective single-center case series

The aim of our retrospective study is to analyze how spinopelvic dissociations (SPDs) were treated in a single center trying to better understand how to improve surgical and non-surgical options. Twenty patients of a single center surgically treated for SPDs between 2013 and 2021 were retrospectively included in this study. Three surgical techniques have been used: modified triangular stabilization, triangular stabilization and double iliac screws stabilization. Follow-up was assessed for up to 11.6 ± 9.9 months through ODI, MRS, NRS, IIEF or FSFI, a CT scan and whole spine X-ray examination. Twenty patients were admitted to our ER for traumatic spinopelvic dissociation. Surgical treatment for spinopelvic dissociation has been performed on average 11.5 ± 6.7 days after the trauma event. Eighteen fractures were C3 type and two C2 types. Neurological examination showed nerve root injury (N2) in 5 patients, incomplete spinal cord injury (N3) in 4 patients and cauda equina syndrome in two patients (N4). In case of neurologic deficits, routinary nerve decompression was performed. Three different surgical techniques have been used: 8 triangular fixations (Group 1), 6 modified triangular stabilization (Group 2) and 6 double iliac screws triangular fixation (Group 3). In patients with post-traumatic neurological deficit, decompression surgery and fracture reduction seem to be associated with clinical improvement; however, sexual disorders seem to be less responsive to the treatment. Some open stabilization techniques, such as the double iliac screw, could help in restoring the sagittal balance in case of severe deformities.


Introduction
Spinopelvic dissociations (SPDs) are unusual high-energy injury fractures (less than 1% of all spine fractures), characterized by transverse and bi or unilateral longitudinal multiplanar sacral fractures forming an H-, Y-, T-or U-shaped pattern. Instability is due to a lesion of one of the articular processes of L5/S1 that can lead to fracture reduction problems and lumbosacral pain [1].
A spinopelvic dissociation results from two major mechanical components: axial load first produces bilateral vertical fracture; then, due to vertical instability and high-energy transfer, the sacrum is forced in a rotational movement that causes an additional horizontal fracture, usually between S1 and S2. The result is complete instability: the rostral part of the sacrum stays attached to the lumbar spine, while the caudal part remains connected to the posterior pelvic ring [2] Complex sacral fractures with spinopelvic instability are rare. Nork et al. reported a case series of 442 pelvic ring injuries of whom 13 (2.9%) were identified as "U-shaped" sacral fractures [3].
A tremendous amount of force is necessary to produce this kind of injury and the survivability is low, especially because of associated soft tissue, bone, visceral and neurological lesions.
The initial neurological status following trauma is a cause of debate for the type of surgical indication: actually there is no consensus regarding the different type of treatment to perform (conservative, minimally invasive surgery, open surgery).

Materials and methods
The aim of our retrospective study is to analyze how SPDs were treated in a single center trying to better understand how to improve surgical and non-surgical options.
Twenty patients of a single center (Spine Surgery Uniti, Careggi Hospital, Florence), surgically treated for SPDs between 2013 and 2021, were retrospectively included in this study; patient characterizations are widely reported in Table 1.
Advanced trauma life support (ATLS) was followed to all the patients at first assessment and the orthopedics principles of damage control were carried out: urgent surgical procedures were performed in the emergency room if life-threatening injuries were assessed.
AO classification of sacral fractures was used to classify the fractures, along with pre-and postoperative neurological status, through ODI, MRS and NRS, and pelvic parameters with sacrococcygeal angle.
The integration of total-body computed tomography (CT) scan with 3D reconstruction into early trauma care was used to significantly improve the probability of early diagnosis and the consequent survival rate in patients with polytrauma.
AO spine classification was independently utilized by a neurosurgeon and a trauma surgeon with 25 years of experience in the treatment of spine fractures with 100% concurrence (assessed through Cohen's kappa calculation, k = 1.00) on the definition of the different sacral fractures with involvement of the posterior pelvic ring and the associated neurological status and additional conditions [4].
Informed consent for proposed surgery was collected for each patient.
LSCIS treatment algorithm was used to help in the decision making for the treatment of traumatic spinopelvic dissociation.
All patients were treated as quickly as possible compatibly with additional skeletal and internal organ trauma and hemodynamic and respiratory stability in an average time of 11 ± 6.9 days. Whenever a neurological deficit was found, surgery was performed within 24 h from trauma and was postponed only in the presence of a life-threatening condition requiring emergency treatment.
Depending on the degree of dissociation, comminution and intraoperative reducibility, 3 surgical techniques have been used: modified triangular stabilization, triangular stabilization and double iliac screws stabilization.
Modified triangular stabilization was used in case of low degree of deformity and limited sacro-iliac disjunction; triangular stabilization in case of spinopelvic dissociations with moderate rate of deformity and displacement of sacroiliac joint along only one axis; and stabilization with a double iliac screw in case of more complex fractures.
All three surgical techniques were performed by 2 neurosurgeons with at least 10 years of experience with spinal trauma. Percutaneous iliosacral screw placement, in the case of triangular stabilization, was performed by an orthopedist with 20 years of experience in treating sacral trauma.
In every surgery titanium Solera (Medtronic ® ) and Matta system (Stryker ® ) were used.
The modified triangular stabilization is an open technique: first the pedicle screws in the lumbar pedicles are inserted; then caudal screws are implanted into the iliac bone through the posterior-superior iliac spine (PSIS) and parallel to the sacroiliac joint. Connecting rods are inserted and tightened initially only over the proximal pedicle screws of L4. Then reduction is carried out using pedicle screws as a guide for reduction in vertical and horizontal direction, a distractor over pedicle screws or a bone hook to pull the iliac wing. At this point, the connecting rod was tightened over the distal (PSIS) screws, stabilizing the fracture. In order to obtain stabilization in the horizontal plane, a 6-mm rod is inserted as a transversal cross-link between the two longitudinal connecting rods.
In case of mild S1 body comminution, a mono/bilateral iliosacral screw was positioned to stabilize the horizontal shear of fracture instead of using the transverse connecting rod, along with the lumbosacral stabilization. Before placing these iliac screws, rods were secured to the lumbosacral pedicle screws.
In a percutaneous way, with the help of fluoroscopic guidance trough a C-arm, a true lateral projection is obtained with superimposition of the iliac cortical densities (ICD) and S1 body cortices. The ICD marks the anterosuperior boundary of the safe zone for an iliosacral screw insertion which may injure the L5 nerve root if it penetrates this cortex. The iliosacral screw is placed through a skin incision made at the identified site using a guidewire tapped or drilled in the selected entry point under constant monitoring with fluoroscope in lateral, inlet and outlet projection.
The double iliac screw technique is used to obtain an easier and better reduction in case of a high displaced fracture. With this technique, the upper iliac screw is used to place a screwdriver as a lever to reduce the fracture, while the inferior iliac screw allows to block and secure the construct placing a first short rod between this and the L5 pedicle screw. A second rod is then placed between the first iliac screw and the L4 pedicle screw. Moreover, this method allows avoiding sacrum screw placement to spare it from the axial load, avoid rod passage and bending difficulties and enable a more extensive sacral decompression. Double iliac screws create a more stable construct and allow a better reduction because more strength can be applied during reduction's maneuvers and permits to keep tension during the following operations (counterlateral pedicle screws placement, cross-link placement). Reduction of the fracture was also obtained through closed technique by prone positioning with abdominal support and moderate traction of the lower limbs in order to allow, as far as possible, the re-establishment of the sacral angle.
In all treated cases direct decompression by laminectomy, removal of present fracture fragments, and debridement of neural foramen was performed if neurological deficit was present.
Clinical follow-up was assessed for up to 11.6 ± 9.9 months by evaluating ODI, MRS, NRS and International Index of Erectile Function (IIEF) or Female sexual function index (FSFI) [5,6]. Postoperative radiological evaluation was made with a CT scan of the lumbar spine and an X-ray examination of the whole spine under load.

Results
Twenty patients (10 females and 10 males) were admitted to our ER for traumatic spinopelvic dissociation. The patient's average age is 41.8 ± 13 years. A whole-body CT scan was performed to detect any bone and visceral lesion. Pelvic ring injury occurred with different traumatic mechanisms: in 9 patients for suicidal jump, in 8 patients for a major motor vehicle accident, while 3 patients fell occasionally from height. Surgical treatment for spinopelvic dissociation has been performed on average 11.5 ± 6.7 days after the trauma event due to different conditions that could have postponed the surgery. Nineteen patients suffered skeletal fractures elsewhere, 13 of whom required immediate surgery; 10 patients had internal bowel injury, 1 of whom required immediate intervention; 8 acute respiratory disorders and 11 patients hemodynamic instability.
In our case series, 18 fractures were C3 type and two C2 types. In 10 cases there were associated anterior pelvic ring injuries (M3), 4 of these presented open book fracture (> 2 cm, AO surgery references) so that an early stabilization was performed with an internal pelvic orthotic device in the same surgical time of the posterior lumbopelvic fixation. Sacroiliac joint injury (M4) was found in 12 patients. Six patients had concurrent anterior pelvic ring and sacroiliac joint injury (M3 + M4).
Neurological examination showed nerve root injury (N2) in 5 patients, incomplete spinal cord injury (N3) in 4 patients and cauda equina syndrome in two patients (N4).
In case of neurologic deficits, routinary nerve decompression was performed. Improvement of neurological status has been achieved in 9 cases out of 11, with a complete recovery in 4 cases (2 motor deficit, 1 sensitive deficit and 1 sphincter function). In 5 cases we observed an improvement in motor function.
Three different surgical techniques have been used, depending on the grade of sacroiliac joint injury, comminution and intraoperative reducibility of the fracture: 8 triangular fixations (Group 1), 6 modified triangular stabilization (Group 2) and 6 double iliac screws triangular fixation (Group 3).
One case of postoperative CSF leakage occurred in our case series and required surgical intervention. One patient had a wound complication not requiring surgery. Four patients developed complications related to orthopedics surgery. Three patients presented hemodynamic instability following SPD stabilization surgery needing a transfusion.
Mean values of outcome scale used during follow-up (Odi, MRS and NRS) are reported in Table 2.
Mean values of pre-and postoperative sacrococcygeal angle (SCA) are reported in Table 3.

Discussion
Spinopelvic dissociation is a rare type of injury and, even if a lot of studies have tried to report their experiences, there is no uniform protocol in surgical treatment, reduction techniques and timing for any nerve decompression.
Early operation, with consequent early mobilization, can lead to improved long-term outcomes, and quality of life compatibly with hemodynamic and respiratory stability and the presence of additional lower extremity fractures that may require a prolonged period of non-weight bearing [1,7]. Evaluation of neurological state after the trauma is one of the main hinge points in the definition of a correct algorithm treatment for SPDs.
Gibbons classification of cauda equina impairment firstly tried to assess the correlation between neurological status and sacral fracture type [8].
Severe neurological complications, ranging from incomplete radiculopathy to bowel and bladder dysfunction, ruptured nerve roots and complete cauda equina syndrome, may occur; the incidence of these severe complications may reach 80% of patients [9].
Neurological recovery and clinical outcome seem to be associated with the degree of initial translation displacement of the transverse sacral fracture, which could be related to bilateral sacral nerve root compression [10].
Sexual dysfunctions after pelvic injuries are common but underestimated complications and are generally caused by high-energy trauma in young and usually sexually active subjects [11]. Fractures that involves bilateral pubi rami, sacral neuroforamen and fractures or dislocations of the sacro-iliac joints are more frequently associated with sexual disorders. Discomposed fractures with a high degree of deformity have been associated with a higher likelihood of developing sexual disorders [12].
In our series, we observed a quit high rate of residual sexual disfunction, especially in patients with highly displaced fracture (Group 3). Another issue to consider is time of follow-up, because patient with a longer follow-up tend to have a better sexual function outcome.
Some studies showed neurologic improvement regardless of surgical or nonsurgical management, while others have reported better outcomes with decompression of the fracture site or full sacral laminectomy [2,13].
The timing of any surgical treatment should be chosen on the basis of treatment goals, the patient's general medical status, and the invasiveness of the surgical procedure [14]. Overly aggressive early surgery can lead to unacceptable intraoperative blood loss, soft-tissue breakdown, and infection. On the other hand, delayed decompression of neural elements beyond 2 weeks may adversely affect chances for neurologic recovery. Thus, the ideal timing for the surgery seems to be between 1 and 2 weeks.
In our case series the average interval between the trauma and the lumbopelvic fixation was 11 days.
Probably high-energy pelvic trauma may be associated with direct damage to soft tissue, sacral and hypogastric plexuses, or sphincter muscles. Therefore, posterior decompression of nerve structures involved in these functions, even if performed early, is less likely to be associated with improved sexual and genitourinary function in contrast to motor functions, which seem to respond well to early decompression.
In case of complete spinal cord injury, we didn't obtain any improvement, nor in motor or sensitive function, nor in genitourinary or sexual disorders. In patients with incomplete spinal cord injury, instead, a complete resolution was achieved in 2 cases and an improvement in 2 cases. All patients with motor deficit obtained an improvement and a complete resolution was observed in 2 cases.
Although no statistical significance has been achieved, our results seem to confirm that global clinical outcome is particularly related with fracture displacement and grade of comminution. Indeed, patients who underwent triangular fixation show better results in outcome scales used at followup evaluation ( Table 2).
Different techniques have been proposed to stabilize spinopelvic dissociations.
The two main interventional options are iliosacral screw fixation [15] and lumbopelvic fixation (LPF) [16]. A study by Kelly et al. demonstrated that both techniques can be used without any difference in length of stay or need for ICU, however, LPF allows immediate weight bearing by-passing direct charge on the damaged sacrum and reconnecting the hemipelvis to the axial skeleton [17]. Moreover, with LPF it is possible to cranially lengthen the stabilization in case of associated lumbar fracture. In our cohort, 4 patients presented a lumbar fracture that required cranial elongation of LPF.
The best choice for biomechanical efficiency is triangular stabilization (TPO). It consists of a lumbar pelvic fusion with mono or bilateral iliosacral screws. This allows counterbalancing the vertical and horizontal forces on the posterior pelvic ring during unipodal stance providing multiplanar stability [18]. Mouhsine et al. showed similar stability and good rate of horizontal and vertical reduction and stability with a modified triangular stabilization (mTPO). It consists of a lumbopelvic fixation with a transversal connector between the two rods instead of the iliosacral screws, keeping sparing axial load from the sacrum such as in TPO [19], (Figs. 1 and 2).
The patients are mostly hemodynamically unstable because of trauma and a minimally invasive approach may be indicated. Percutaneous screws and rod placement have shown good accuracy and fracture stabilization with very little intra-and postoperative blood loss [20].
The possibility to navigate and minimally invasively insert sacral and iliac screws with the support of 3d fluoroscopy or CT images (o-Arm) turns into greater safety for the surgeon in the placement of difficult percutaneous screws, avoiding open approaches, long surgery time and other complications related to open reduction and internal fixation [21].
On the other hand, in case of higher grade fractures and deformities, often associated with neurological deficits, a percutaneous stabilization could preclude the possibility of 1 3 obtaining a better reduction, decompression of neural structures by an open approach and overall stability [22]. SPD with high deformity grade is unlikely to be reduced by positioning patient prone and creating postural pelvic extension [3] or applying caudal (bifemoral skeletal pulling) and cranial (Mayfield's tongue) traction [13]. Open methods of reduction allow disimpaction and decompression if needed. Systems of lever using Schanz pin on lumbar pedicles, sacral body and ilium screws have been described [16] (Figs. 3, 4 and 5).
In our series, patients were positioned prone with the abdomen unloaded and soft traction was performed on the lower extremities to achieve initial reduction by closed maneuver. If adequate reduction of the fracture was not evident at fluoroscopy, an open approach was used using reduction technique with the two iliac screws or Schanz pin and transverse bars to avoid losing reduction traction.
Pelvic incidence and sacrococcygeal angle are the radiological parameters used to assess reduction and seem to be associated with the consecutive quality of life [23,24].   In our series, pelvic parameters were evaluated postoperatively and with remote follow-up, performed on average 12 months after surgery ( Table 3). The degree of reduction and the sagittal balance obtained are superimposable in the three different surgical techniques performed ( Fig. 6  and 7).

Conclusion
Spinopelvic dissociation is a very impactful condition related to high impact injury and is often associated with neurological impairment, soft tissue injury and deformity.
In patients with post-traumatic neurological deficit, decompression surgery and fracture reduction seem to be associated with clinical improvement; however, sexual disorders seem to be less responsive to the treatment.
Some open stabilization techniques, such as the double iliac screw, could help in restoring the sagittal balance in case of severe deformities.
This retrospective study contains several limitations (low number of patients, absence of a control group, relatively short follow-up time).
Therefore, a prospective study with a closer clinical follow-up, with a higher number of patients and taking into account the possibility of percutaneous treatment in low deformities, could help in the definition of a treatment algorithm for spinopelvic dissociations.
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