Thoracolumbar (TL) burst fractures are relatively common, occurring in approximately 20% of all vertebral fractures1, and are characterized by retropulsion of the fractured middle column fragments into the spinal canal. Although the management of TL burst fractures has been extensively studied, the indication for surgical treatment remains under debate. Previous studies have reported that long-term functional outcomes may not differ substantially between operative and nonoperative treatment for neurologically intact TL burst fractures1. Nevertheless, these comparative studies were launched decades ago, making their results not applicable in this era when surgical techniques have substantially improved since then.
Recent advances in surgical techniques may have changed the surgical indications. Recently, minimally invasive approaches for TL injuries have become popular, and good results have been reported. Although their sample sizes are small, studies about the emerging novel techniques and implants support surgical treatment for neurologically intact TL fractures1.
Generally, surgical treatment of neurologically intact TL fractures aims to ensure good alignment correction, reduction of fracture fragments with ligamentotaxis, and secure fixation2,3. In patients with neurological symptoms, direct or indirect decompression of the neural structure is added to these aims. There are variations in the surgical techniques used for posterior fixation of TL burst fractures, such as surgery with and without fusion, the use of vertebroplasty, different numbers of fixation levels, and the use of additional screws on the fractured vertebrae.
Non-fusion fixation using percutaneous pedicle screws (PPSs) is commonly performed because it is less invasive and allows segmental motion after implant removal. The advantages of PPS over conventional open techniques are not limited to smaller skin incisions; PPS is associated with less paraspinal muscle damage compared to an open approach4. Moreover, a human cadaver study reported that PPS reduces the risk of medial branch nerve injury, which leads to multifidus muscle denervation5. Currently, a TL fracture is among the most common indications for minimally invasive surgery using PPSs, and a minimally invasive PPS system without fusion is reportedly associated with improved surgical outcomes in patients with TL burst fractures2,3.
Reduction techniques are also a topic of interest. Since the 1980s, the Schanz screw system has been used for TL burst fracture treatment; this system allows good angular correction, vertebral height reduction, and reduction of retropulsion fragments by ligamentotaxis. Good results have been reported with the Schanz screw system6. However, the original Schanz system appears unsuitable for percutaneous use because the connectors are too bulky and use a side-loading system.
In contrast, the designated PPS system, which was developed in the 2000s, has been widely used for various conditions7. Although it is associated with less invasiveness to back muscles, one drawback of conventional multiaxial screws (MAS), compared with the Schanz system, is that screws have less angular stability due to a mobile screw head. Monoaxial screws, which have better angular stability than MAS, are also available as PPS options. However, it is often technically demanding to align all screw heads in the same plane as rods percutaneously without any angulation of the screws to avoid excessive mechanical stress on the screws or bones. Additionally, creating lordosis after screw insertion is almost impossible when monoaxial screws are used.
To overcome these issues, the sagittal adjusting screw (SAS) system was introduced in 2013 and was first aimed to correct spinal deformity secondary to fractures. The SAS is a monoaxial screw system with a fixed head that resembles a common head-loading pedicle screw; it has a concave sliding saddle that allows lordotic sliding of the rod in the sagittal plane after screw insertion. Since then, the use of SAS has expanded among acute TL burst fractures8,9 as well as elective procedures including correction of spondylolisthesis10. The SAS only allows motion on the sagittal plane, allowing both secure fixation and angular reduction, which is usually impossible after screw insertion using conventional monoaxial screws.
One biomechanical study demonstrated that the SAS system has better force-displacement properties and fatigue test results than other head-loading PPSs, equivalent to the Schanz screw system. Trauma reduction devices can be attached to the extension towers of the SAS system and, therefore, both distraction and angulation forces can be applied at the instrumented levels using such a device9. Good results have also been reported for such trauma reduction devices used for TL fractures8.
The aim of this protocol is to describe the technique for alignment correction and fracture reduction methods using the SAS system in TL burst fractures and discuss the advantages of the SAS system. In the following protocol, PPS placement and fracture reduction using the SAS system and trauma reduction device are outlined. We also show representative cases demonstrating the results of this procedure.