Abstract
Background Stent screw-assisted internal fixation (SAIF) has been shown to be a valid minimally invasive alternative in the treatment of high-grade osteoporotic and neoplastic fractures presenting with burst morphology, extreme collapse and kyphosis, extensive osteolysis, large pseudoarthrotic clefts, and pedicle or middle column involvement. However, the presence of local deformity and/or posterior tension band injury (as for osteoporotic fracture [OF] 4 and OF 5 fractures, according to the AO Spine-DGOU OF Classification) ideally requires a posterior fixation in addition to an armed kyphoplasty. For these cases, we have built upon our previous work that associates a posterior fixation with a SAIF by actually integrating the SAIF into the posterior fixation construct (SAIF-Rod).
Objective To describe the procedural steps and discuss the mechanical advantages of the novel technique called SAIF-Rod and present the results of our initial case series.
Methods After vertebral body stent expansion within the index vertebra, augmentable screws from the same set as the posterior fixation are introduced via K-wire exchange into the stent lumen. Kyphoplasty augmentation is performed through these screws. A posterior fixation performed above and below the index vertebra is connected to the screws at the index level. Rod-bending and compression maneuvers are used to address residual deformity that could not be corrected through the SAIF alone.
Results A total of 21 patients (13 men) with a mean age of 76 years (interquartile range [IQR] 65–80) and with neoplastic (19%), traumatic (10%), and osteoporotic (71%) thoracolumbar fractures were treated with SAIF-Rod at our institution. Demographic and surgical data for a minimum follow-up of 12 months were presented. No major early or delayed complications (Clavien-Dindo grades 4 or 5) occurred. Mean intraoperative blood loss (150 mL, IQR 100–400), operating time (318 minutes, IQR 263–346), and length of stay at the hospital (7 days, IQR 5–11) were recorded.
Conclusion In selected cases, SAIF-Rod represents a minimally invasive surgical alternative for the treatment of high-grade osteoporotic, traumatic, and neoplastic fractures, usually accompanied by deformity.
Level of Evidence 4.
- kyphosis
- metastatic vertebral fractures
- minimally invasive spine surgery
- vertebral augmentation
- osteoporotic vertebral fractures
Introduction
Vertebral augmentation (VA) techniques are routinely used for the treatment of osteoporotic and neoplastic fractures.1–3 Such procedures are efficient not only for pain palliation but also in reconstructing and stabilizing vertebral body (VB) injuries through a minimally invasive approach with the aim of avoiding more extensive anterior column reconstruction procedures in this frail patient population.
The literature reports a wide variety of devices currently in use in VA procedures, such as balloon kyphoplasty, SpineJack (Stryker, Kalamazoo, Michigan, USA), or VB Stent (VBS, DePuy Synthes-Johnson & Johnson).1,4,5 Stent screw-assisted internal fixation (SAIF) has recently been proposed as an alternative to these techniques.6–12
In SAIF, the VBS implant is connected to the pedicle through the insertion of a percutaneous transpedicular cannulated fenestrated screw, followed by cement deposition through the screw. In this way, the VBS obtains VB height restoration, creates an internal scaffold of the VB, ensures safer cement deposition and anterior column reconstruction, and anchors the VBS-cement implant to the posterior elements through the pedicle, thereby reducing the risk of VBS mobilization and the occurrence of middle column and pedicle fractures.
Biomechanical models have demonstrated advantages of SAIF over standard VA in restoring the load-bearing capacity of the anterior and middle spinal columns and in reducing bone strain in the osteoporotic lumbar spine and in an extensive neoplastic lytic model.7,8 However, a “standalone” SAIF may in certain cases result in insufficient correction of regional deformity caused by the index fracture and so may predispose a patient to loss of correction in the long term, deformity-related back pain, andadjacent-level fractures. Therefore, for cases with marked deformity and/or posterior tension band injury, a posterior fixation is usually considered.12
The association of SAIF alongside a posterior instrumentation has therefore been proposed for selected complex cases as a means of combining the advantages of both techniques (SAIF + Fix).11,12 However, this procedure does not allow a true integration of both systems, seeing that they remain separate in situ and therefore may fail to reach their full synergistic potential, discussed in further detail in this report.
We have overcome this setback by inserting, into the SAIF, screws from the same set as those used for the posterior spinal instrumentation. This effectively allows the integration of the SAIF and the posterior instrumentation into a single construct. In this article, we present the procedural steps of the posterior fixation-integrated SAIF technique (SAIF-Rod) and focus on its potential advantages, as well as present our initial case series results.
Methods
Preoperative Work-up
SAIF-Rod represents the third step in the evolution of the SAIF technique (Figure 1a–c). As in the “standalone” SAIF and SAIF + Fix procedures, osteoporotic and neoplastic fractures presenting with burst morphology, extreme collapse and kyphosis, extensive osteolysis, large pseudoarthrotic clefts, and pedicle or middle column involvement represent the principal indications for SAIF-Rod.
The evolution of stent screw-assisted internal fixation (SAIF) and derived techniques. (A) “Stand alone” SAIF performed for the treatment of an osteoporotic fracture, associated here with prophylactic vertebral augmentation in the vertebrae above and below. (B) SAIF + Fix, where a posterior instrumentation is associated with SAIF. In this technique, the SAIF and the posterior instrumentation are distinct. (C) T10–L2 posterior osteosynthesis with SAIF in T12 (SAIF-Rod). Screws placed in the SAIF are the same as those used for the posterior instrumentation. This allows a true integration of the SAIF into the construct.
With special regard to osteoporotic fractures (OFs), the technique addressed the treatment of OF 4 (with loss of integrity of the vertebral frame structure, VB collapse, or pincer-type fractures) and OF 5 fractures (injuries with anterior or posterior tension band failure), according to AO Spine-DGOU OF Classification.12,13 14
The preoperative work-up routinely includes a computed tomography (CT) to evaluate bony injury; magnetic resonance imaging to assess the posterior tension band; and standing x-ray imaging to rule out potential worsening of local deformity in the standing position (Figure 2). For neoplastic cases, the indication is discussed at a multidisciplinary tumor board meeting. In osteoporotic patients, an assessment of the disease is performed in the perioperative period. All patients gave informed consent for their procedure.
Preoperative imaging of a 77-year-old woman with severe back pain following a fall from her own height. (A) Computed tomography (CT) shows an L1 compression fracture, type OF3 according to the AO Spine-DGOU classification. (B) Magnetic resonance imaging demonstrates vertebral edema without ligament injury. (C) Standing x-ray image shows an 18° kyphotic deformity. This figure is original to this submission, so no credit or license is needed.
Technique Description
The patient is positioned prone on a radiolucent operating table under general anesthesia. The patient, table, and arm boards are checked before surgery to be within the inner diameter of the intraoperative CT or cone-beam CT (AIRO, Loop-X; Brainlab AG) to avoid conflict during intraoperative imaging and for ease of use with the spinal navigation system. 2D fluoroscopies are then acquired with the C-arm, in the frontal and lateral planes, for the correct alignment of the spinous processes in the midline and of the endplates, respectively. The procedure can be performed in a percutaneous fashion or through a Wiltse approach via a midline skin incision.
The first part of the procedure is similar to that described for the standalone SAIF technique, with only minor differences described below. Under x-ray guidance, a 4.5 mm (7G) Jamshidi needle, included in the VBS access kit, is positioned through bilateral transpedicular access in the VB, with an oblique lateromedial orientation.6,15 We advise inserting the trocar parallel to the anticipated alignment of the original pre-fracture endplates, at the lowest pedicle border of the fractured vertebra, to obtain the best height restoration during VBS expansion (Figure 3A). Manual drills are placed coaxially through the trocars to create the necessary space for the balloon-mounted VBS, which are then inserted and expanded through balloon inflation on either side of the VB until satisfactory vertebral height is restored and the fracture is reduced (Figure 3B). The balloons and the needles are then removed, leaving 2 K-wires in place. Two cannulated fenestrated screws, from the set used for the posterior fixation (Viper Prime system, DePuy Synthes), are introduced over the K-wires (Figure 3C); this is different from the screws described for the standalone SAIF technique (injection pin, 2B1, Milan, Italy). The screws are inserted into the lumen of the stents, without breaching the anterior cortex and ensuring that the screwheads are settled so as to align later with the screwheads of the posterior fixation. Care is given to avoid conflict with—and potential mobilization of—the stents; real-time fluoroscopy is performed to this end during screw insertion. Polymethylmethacrylate cement is injected through the screws inside the VBS using the dedicated cannulas in the screw set, under fluoroscopic control for instantaneous detection of any cement leakage (Figure 3D–E). The injection cannulas are then removed, leaving the screws in place.
Procedural steps, performed through a Wiltse approach. (A) Trocar access parallel to the anticipated alignment of the original pre-fracture endplates to allow the greatest possible vertebral height restoration during vertebral stent expansion. Stents have not been expanded yet. (B) Stent expansion with vertebral body height restoration. (C) Screws are inserted in the lumen of the stent. (D and E) Stent-cement complex is anchored to the posterior elements by the screws. Anteroposterior and lateral x-ray images after cement injection. (F and G) Intraoperative 3-dimensional imaging confirms correct position of the transpedicular screws above and below the stent screw-assisted internal fixation. (H) Final x-ray image after rod placement. (I and J) Radiological follow-up. (I) Preoperative standing x-ray image. (J) Postoperative x-ray image showing the stability of the construct, with markedly reduced local kyphosis (4°).
The second part of the procedure consists of the posterior transpedicular spinal fixation itself, which our group standardly performs using spinal navigation. However, fluoroscopy-guided screw placement can also be performed. If a Wiltse approach is used, we do this through a midline skin incision and bilateral fascial incisions. If a percutaneous approach is used, a small—4- to 5-cm long—midline skin incision is taken down to the thoracolumbar fascia, which is opened on either side of the spinous process and a navigation reference star is attached to it. Intraoperative 3-dimensional (3D) imaging is acquired for automatic navigation registration with the patient’s anatomy and is also used to control the radiological outcome of the SAIF (ie, the first part of the procedure). Registration accuracy is verified for each vertebra using the navigation pointer. In the percutaneous technique, the navigation pointer is used to plan the paramedian skin incisions, using its trajectory projection function. Entry points and transpedicular trajectories are planned out once on the bony surface, using the navigated drill-guide (BrainLab AG) and the navigation system’s “screw planning” function to determine the ideal screw length and diameter (DePuy Synthes-Johnson & Johnson, VIPER PRIME System). A 2.4-mm drill is then used to create a transpedicular channel, through which a K-wire is inserted, subsequently used to guide screw insertion in addition to direct screw navigation using the navigated screwdriver. A second 3D image acquisition is performed to confirm screw placement (Figure 3F–G). The reference star is removed. If indicated, screw cementation is performed under fluoroscopy. Rods are modeled to the target spinal curvature and are fixed to the screwheads on either side, settling the rod in the SAIF screwhead first to reduce mechanical stress on the SAIF. In addition to the height restoration of the fractured vertebra obtained using SAIF, rod-bending and compression maneuvers can be used at this point to address residual deformity (Figure 3H).
Postoperative Follow-up
Clinical and radiological follow-up is identical to that in patients having undergone standard spinal fixation. Patients are allowed to stand and walk on the same day of the procedure. Anteroposterior and lateral standing radiography are performed prior to discharge (Figure 3I–L). Patients are followed up at 1.5, 3, and 12 months with anteroposterior/lateral standing radiography.
Results
Data from the first 21 patients (13 men and 8 women) with thoracolumbar fractures treated at our institution with the SAIF-Rod technique from April 2017 to September 2023 were analyzed. Mean age was 76 years (interquartile range [IQR] 65–80). Four patients presented with neoplastic fractures (19%), 2 with traumatic fracture (10%), and the rest with OFs (15 patients, 71%). The minimum follow-up was 12 months, and only 1 patient was lost to follow-up before their first appointment due to death from the primary cancer. Regarding surgical technique, a posterior decompression of the spinal canal was also performed in 4 cases (19%) because of associated spinal stenosis. A short posterior instrumentation, with a fixation of 2 segments only, was performed in 13 patients (62%). No major complications (Clavien-Dindo grades 4 or 5) occurred. Minor early complications included a self-resolved hematoma (grade 1) and 2 moderate (grade 3) events that required revision surgery (a wound infection and an intraoperative decompression for cement leakage). Regarding delayed complications, 3 cases of screw mobilization and 1 wound infection were recorded, ultimately requiring revision surgery (Clavien-Dindo grade 3). The mean intraoperative blood loss was 150 mL (IQR 100–400), while the mean operating time was estimated at 318 minutes (IQR 263–346). The mean length of hospital stay was 7 days (IQR 5–11).
Discussion
SAIF-Rod is a previously undescribed procedure for the management of vertebral compression fractures with local deformity that integrates the SAIF into the posterior instrumentation by using the same screws for the SAIF as for the posterior osteosynthesis, thereby forming a single solid construct.
Standalone SAIF offers a useful alternative for the treatment of higher-grade osteoporotic and neoplastic fractures where standard VBS presents with the risk of dislocation from the VB due to wide cortical bone erosion, and highly fragmented or poor residual bone stock in the VB. Although standalone SAIF may well offer a reasonable option in compromised patients otherwise ineligible for open surgery, it may nevertheless provide insufficient stabilization when VB height loss and posterior tension band injury are marked and so cause significant regional kyphotic deformity.6–11 Management options in such cases include short-segment fixation, which comes with the advantage of preserving adjacent motion segments as compared with longer instrumentations but is associated with an implant failure rate (and subsequent kyphosis progression) that ranges from 9% to 54%.16–18 Outcomes improve when the fractured vertebra is also included into the posterior construct, especially in cases of short instrumentations, as this provides greater resistance to tension forces, but such a configuration still does not provide the anterior support that comes with a corpectomy or, in select cases, with VA.16,19–22
In contrast to previously described combined approaches, which associate a vertebroplasty or kyphoplasty of the fractured vertebra with a posterior instrumentation, the SAIF + Fix technique associates the advantages of the standalone SAIF with that of a posterior osteosynthesis.11,12 However, as in the other combined techniques, SAIF + Fix still does not provide a true integration of the 2 systems, as the screws within the SAIF are not connected to the posterior fixation, obliging the posterior construct to “skip” a point of anchorage (much-needed in osteoporotic patients), thus exposing it to the risks of a lever arm.
SAIF-Rod, in contrast, strengthens the stabilization of the anterior and middle columns obtained through SAIF at the index level while at the same time supporting the posterior column. Indeed, anchoring the VBS to a posterior construct effectively minimizes the mechanical stress on the fractured vertebra, as it is “protected” by the instrumentation of the surrounding segments. At the same time, it provides the posterior construct with an anterior support, while allowing to avoid a “skip” level—that is, a level without screws—thereby acting against loosening of the posterior fixation.18,23–26
Furthermore, integrating the SAIF’s screwheads into the posterior rod system allows for additional deformity correction through compression—that is, lordotizing—maneuvers, otherwise not possible either with standalone SAIF or with SAIF-Fix. Indeed, screws inserted in fractured vertebrae act as a push point and, when connected to the rods, provide lordotic forces and therefore improved correction of deformity.16
Fenestrated-screw cement augmentation of the instrumented vertebrae above and below the SAIF increases resistance to pullout and screw loosening in osteoporotic and oncological patients with poor bone stock.23–27 Moreover, the provision of anterior support through SAIF-integrated screws in the index fracture may allow a reduction in the length of the posterior construct.
SAIF-Rod is an image-guided, minimally invasive technique that can be performed through percutaneous or Wiltse approaches. However, our group favors Wiltse approaches, as it reduces muscle trauma and allows an easier access to the screwheads, facilitating rod-based deformity correction.
The main indications for SAIF-Rod are high-grade osteoporotic and neoplastic fractures, usually accompanied by deformity. We do not suggest using SAIF-Rod, VA, or SAIF in trauma in young patients, as their bone quality is presumed to be satisfactory and large volume implants in the VB with cement-augmentation may halt their spontaneous osseous healing. The stent-screw system is currently not available for use in the United States because it lacks US Food and Drug Administration approval.
Limitations
The preliminary results of our initial case series reported here were inferred from a small patient sample. Despite its theoretical advantages, larger studies are required to clinically validate the biomechanical rationale and efficacy of the SAIF-Rod technique. The retrospective analysis and the absence of a standardized clinical and radiological follow-up also limit the generalizability of our results at this time. Future investigations could incorporate a control group to enable comparison between SAIF-Rod and other similar combined procedures. Moreover, the higher costs associated with VBS compared with standard vertebroplasty may limit the broader implementation of the SAIF-Rod technique, particularly in the absence of evidence regarding its clinical superiority.
Conclusion
SAIF-Rod represents a minimally invasive surgical alternative for VB restoration of axial loading capacity and regional spinal deformity correction in the presence of severe vertebral compression fractures in osteoporotic or neoplastic settings.
Footnotes
Funding The authors received no financial support for the research, authorship, and/or publication of this article.
Declaration of Conflicting Interests The authors report no conflicts of interest in this work.
- This manuscript is generously published free of charge by ISASS, the International Society for the Advancement of Spine Surgery. Copyright © 2026 ISASS. To see more or order reprints or permissions, see http://ijssurgery.com.
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