With the development of surgical technology, bilateral nerve roots can be decompressed via the single transforaminal approach . With this method, the hybrid technique using a combination of a UPS plus a single contralateral TLFS in TLIF, pioneered by Jang et al. in 2005 , has gained increasing popularity due to diminished soft tissue injuries, reduced estimated blood loss, lower operative costs, and reduced potential risk of neurological injury [6, 8, 15], compared with the standard BPS method. Recent biomechanical data suggest that the new fixation system provides the same degree of stability and supports the same amount of stiffness in all directions, such as flexion–extension, lateral bending, and axial rotation, compared with the BPS method [9, 16–18]. Moreover, some clinical assessments demonstrated that although there was no significant difference between the two methods in terms of clinical outcome, fusion rate, or complication rate, the operative time, blood loss, and cost were significantly reduced in the hybrid method [7, 8].
However, the hybrid technique is technically more challenging and has been associated with neurological injuries. During insertion of the TLFS, which was devised by Magerl  as a less invasive alternative for posterior pedicle screw stabilization, the incidence of intraoperative complications including partial dorsal laminar breach or penetration of the screw into the spinal canal could not be completely avoided [20, 21]. In addition, increased exposure to intraoperative radiation should not be ignored. To increase the safety and accuracy of TLFS placement, Grob and Humke  described a prototype device that they invented to percutaneously insert the TLFS as a supplementary posterior fixation method to anterior lumbar interbody fusion (ALIF). However, their study lacked technical details and clinical outcomes. Jang et al.  introduced a guide device for the percutaneous placement of the TLFS after ALIF. Unfortunately, their device is not commercially available and, thus, their technique cannot yet be widely used. Shim et al.  reported on their experience with a fluoroscopy-assisted percutaneous TLFS fixation technique without the use of a guide device. Although this technique allows the surgeon to obtain simultaneous intraoperative multilevel visualization of the proposed screw trajectory under fluoroscopic guidance, 10% of the screws violated the lamina wall, with 15% of the screws found to be in an imperfect position. Recently, some studies have demonstrated that the use of CT, or a combination of CT and fluoroscopic guidance, can dramatically reduce the difficulty in implanting the TLFS by providing both three-dimensional landmarks and real-time imaging [24, 25]. However, these techniques may increase the exposure to radiation and the operation time, and the potential for inaccurate screw placement cannot be completely avoided.
Besides the auxiliary methods, a detailed knowledge of facet anatomy and corresponding radiographic criteria is required for the safe placement of a contralateral TLFS. Lu et al.  conducted an anatomic study in 30 dried lumbar spines to measure the screw path length, caudal and lateral angles, and superior and inferior lamina border thicknesses from L1 to L5 for insertion of the TLFS. In the human cadaveric study by Phillips et al.  the radiographic data suggested that the radiographic views identified to achieve proper placement of the TLFS were a true lateral, AP, 45º oblique, and AP view with the X-ray beam at a 30º to 45º cephalad angle (“spinal outlet” view). These studies provide the relevant data for use of the TLFS and may greatly increase the safety of screw placement. In our study, most patients obtained bicortical purchase. On the one hand, based on the preoperative measurement of 3-dimensional image reconstruction of the CT data of patients and the intraoperative length of probe, the length of TLFS was ensure to be long enough to traverse the facet joints. On the other hand, considering that Asians are smaller in size than Westerner, the TLFS used in our study was 4.0 mm in diameter, which had been proved to be effective . (Magerl inserted a 4.5 mm cortical screw for placing TLFS.) It is vital to ensure that the diameter of screw was no greater than the thickness of inferior border of the lamina, to prevent the lamina from occurring the bicortical purchase.
To ensure the safe placement of a contralateral TLFS in the hybrid technique, we slightly modified Magerl’s technique by adding a small unicortical “hole” adjacent to the facet joint at the contralateral dorsal lamina. Direct visualization of the insertion of the screw against the dorsal cortices of the lamina provides assurance, without the need for fluoroscopy, that the TLFS can be correctly located within the lamina and not entered the spinal canal. Compared with the conventional TLIF technique, our modified technique appears to be technically simple and safe, less invasive, and less expensive. We encountered no screw loosening or breakage and no neurologic injuries, and we attribute the absence of intraoperative complications to the fact that the insertion of the screws was technically easy under direct vision.
Clinically, compared to TLIF, the total operating time and estimated blood loss of the patients treated with our modified technique were reduced, which indicates that the new technique could help minimize the degree of surgical invasion and reduce the length of hospital stay. Moreover, the fusion rate (90.5%) at last follow-up and the position of the screws were satisfactory according to the postoperative CT. Biomechanical stability was ensured by postoperative dynamic X-rays. These results demonstrate that our technique has clinical efficacy and safety, and this appears to be consistent with some of the more recent studies [6–8].
In summary, our modified technique results in significant improvements in both clinical safety and efficacy during the placement of TLFS. Moreover, it reduces the operation time and blood loss and incurs a lower operative cost. However, there are some limitations in our study. Firstly, the sample size is relatively small, further studies are required to confirm the application of this modified technique in the future; Secondly, this modification lacks the partial bicortical purchase, and this difference may account for the reduced TLFS stiffness in axial rotation and lateral bending because the screws may toggle within the cancellous laminar bone. Therefore, the question of whether this technique is biomechanically as effective as the traditional TLFS method is still open to further research. Finally, although, compare with conventional TLIF, our modified technique seems to be more minimal invasive, a better comparison to other minimal invasive fixation (such as MIS-TLIF, in which no contralateral subperiosteal dissection is needed cause contralateral screws replaced percutaneously.) may lead to more clinical significance, which warrant further studies.