The pedicle screw is a cornerstone of modern spinal instrumentation, offering strong fixation for a variety of spinal pathologies such as deformity correction, trauma management, and oncologic reconstructions. The free-hand technique for the thoracic pedicle screw placement was introduced in 2000s [1]. Although image-guided navigation and robotic assistance may facilitate screw insertion, free-hand anatomy-based techniques remain essential for surgical education, rapid decision-making, and managing unexpected equipment failures [2-5]. Unlike lumbar pedicle screws, thoracic pedicle screw insertion was introduced a generation ago, yet it remains a challenging procedure [6]. The primary challenges associated with thoracic pedicle screw insertion arise from anatomical variability of pedicle. The transverse pedicle width of the thoracic spine has been reported to range from 2 to 6 mm, and the medial pedicle angle has been reported to range from -5° to 30° [7]. To accommodate these variations, transpedicular screw insertion requires a medial convergence angle same as the medial pedicle angle, and screw diameters as small as 3 mm may be necessary.

Early free-hand methods relied on entry points that varied at each spinal level according to anatomical variability [1,8]. Several studies have noted that previously published techniques and “thoracic pedicle screw charts” can be difficult to adopt and teach because of variability in entry points and angulations, and have therefore proposed using a uniform entry point instead [2,9,10]. Concerns regarding accuracy led to modifications in which a single-entry point was applied to groups of 3 to 4 consecutive vertebral levels or to triangular anatomical areas. However, substantial variability in pedicle size and transverse angulation across thoracic levels continues to make it difficult to apply a uniform entry-point rule for thoracic transpedicular screws. Since then, several alternative techniques—claiming improved safety and accuracy—have continued to emerge [9-11].

A common indication for thoracic transpedicular screw insertion in oncologic disease is spinal metastases [12]. In metastatic lesions, the pedicle is often compromised because tumor spread commonly begins in the pedicle and lead to its lysis, resulting in thinner pedicles. In addition, for planning and delivering radiation therapy, it is preferable for the screw to be positioned as far from the spinal cord as possible. Moreover, these lesions are frequently osteolytic with poor bone quality, yet strong fixation is still required [13,14].

To achieve this, we developed a free-hand technique that uses a uniform entry point and maximizes pullout strength, tailored to the unique characteristics of the metastatic spine. Therefore, this study aims to identify a uniform entry point that can overcome the limitations of conventional techniques and enhance the precision and reproducibility of screw fixation.

This study was designed as a retrospective analysis of prospectively and consecutively collected data to evaluate the accuracy and feasibility of L-point entry, juxtapedicular, and endplate-parallel trajectory (L-JET) fixation compared with the conventional transpedicular screw in patients with thoracic spinal tumors. Patients were followed for at least 2 years postoperatively to assess the durability and safety of the procedure. The study was conducted at Seoul National University Hospital and was approved by the Institutional Review Board (IRB approval number: 2504-021-1628). Patients who underwent thoracic pedicle screw fixation for extradural spinal tumors between November 2022 and October 2023 were consecutively included. The inclusion criteria were: (1) adult older than 20 years old, (2) extradural tumors, including metastases, requiring pedicle screw fixation at T3–10, and (3) availability of postoperative computed tomography imaging. Screws placed at levels with previous surgical instrumentation or pediculectomy were excluded from analysis. Patient demographics, clinical presentation, indications for hardware placement, radiological studies, operative variables, and length of follow-up were reviewed for each case.

A total of 40 patients who underwent thoracic pedicle screw fixation for thoracic spinal tumor surgery were included in the study. Among them, 108 screws of 22 patients were performed by the L-JET screw fixation, while 98 screws of 18 patients were done by the conventional method. Baseline characteristics are summarized in Table 1. The mean follow-up duration was 12.0±8.9 months in the L-JET group and 18.7±15.3 months in the traditional group, which was not statistically significant (p=0.31). Level-specific analysis from T3 to T10 demonstrated no significant difference in pedicle diameters between traditional and L-JET group at T3 (5.30±0.79 mm vs. 4.83±0.69 mm, p=0.12), T4 (4.83±0.98 mm vs. 4.35±0.85 mm, p=0.17), T5 (4.37±0.88 mm vs. 4.19±0.99 mm, p=0.66), T6 (5.31±1.00 mm vs. 4.43±1.17 mm, p=0.05), T7 (5.05±1.12 mm vs. 4.63±1.16 mm, p=0.28), T8 (4.62±0.61 mm vs. 4.30±1.34 mm, p=0.50), and T9 (5.38±1.08 mm vs. 5.17±0.84 mm, p=0.62). A statistically significant difference was observed at T10 (7.12±1.24 mm vs. 5.27±1.49 mm, p≤0.01).

A total of 108 screws were placed in the L-JET group and 98 in the conventional group in Table 2 (p=0.34). The L-JET group used screws with a significantly larger mean diameter (6.06±0.65 mm) compared to the conventional group (5.74±0.80 mm; p=0.02) (Table 2). Subanalysis by level showed that screw diameter in the L-JET group was significantly larger in both the upper thoracic spine (T3–4; 5.73±0.43 mm vs. 5.00±0.66 mm, p<0.014) and the low thoracic spine (T9–10; 6.83±0.69 mm vs. 6.31±0.70 mm, p=0.02) in Figure 4, whereas no significant difference was observed in the midthoracic region (T5–8, p=0.10). In the L-JET group, the screw diameter was 0.94–1.83 mm larger than the corresponding pedicle width. The conventional group showed variable sizing, with screw diameters both above and below pedicle width. There was no significant difference in overall mean screw length between the L-JET (43.89±5.31 mm) and conventional groups (44.60±4.82 mm, p=0.31). Level-specific analysis showed a shorter screw length in the upper thoracic spine in the L-JET group (39.17±2.31 mm vs. 42.33±4.56 mm, p<0.01), with no significant differences in the midthoracic (p=0.38) or low thoracic levels (p=0.47).

Analysis of screw breach according to the Gertzbein-Robbins grading system is summarized in Table 2. In the conventional group, lateral breaches were observed in 13 screws graded A and 4 graded B, while in the L-JET group, lateral breaches included 60 screws graded A, 28 graded B, and 4 graded C. Although lateral breach was frequent in the L-JET group, this was considered an inherent and predictable aspect of the juxtapedicular insertion technique. Medial breaches occurred in 1 screw graded B in the conventional group and in 2 screws graded A and 1 graded B in the L-JET group. No superior or inferior breaches were observed in either group. No neurovascular events were observed in either group. At final follow-up, radiographic loosening was identified in one patient per group, each involving a single screw at different vertebral levels (right T10 in the conventional group and right T3 in the L-JET group) and not at the upper instrumented vertebra or lower instrumented vertebra; given the extremely low event count and level heterogeneity, statistical comparison was not feasible. Aside from these isolated radiographic findings, no other hardware-related adverse events were noted, and no instrumentation revisions were required in either group.

This study evaluated the safety and utility of the L-JET technique for thoracic spinal tumor surgery. The L-JET technique provides ease of insertion by utilizing a uniform entry and a trajectory comparable to lumbar pedicle screws, thus facilitating surgeon adaptation. Apart from the anticipated lateral breaches associated with the L-JET technique, surgical complications occurred at comparable rates between the L-JET and conventional methods. Furthermore, at a minimum follow-up of 2 years, procedure-related complications were acceptable, supporting the safety of the L-JET technique. The L-JET technique is particularly useful in the thoracic spine, especially in the upper to midthoracic levels with narrow pedicles, as it enables the insertion of larger-diameter screws. Given the established association between screw size and pullout strength, this approach may enhance the robustness of fixation.

One consideration associated with the juxtapedicular technique is the higher frequency of lateral breaches observed in the L-JET group. Although this was anticipated due to the lateralized entry point and juxtapedicular approach, these breaches may result in screw threads becoming exposed along the lateral aspect of the pedicle. However, the rib-pedicle-transverse process unit provides a continuous anatomical barrier, substantially reducing the risk of screw exposure to adjacent neurovascular or soft tissue structures [18,19]. Furthermore, previous studies using extrapedicular or juxtapedicular screw techniques have reported complication rates comparable to those associated with conventional transpedicular screw insertion [18-21]. In the current study, no patient in either group experienced adverse events or required revision surgery related to screw placement for 2-year follow-up. According to our findings, this screw insertion technique may demonstrate an acceptable safety profile.

Prior biomechanical work has shown that even with lateral wall violation, pedicle screws remain biomechanically stable [21]. A meta-analysis reported no significant difference in ultimate pullout strength between transpedicular and extrapedicular screws [22]. Other previous studies have noted that the pedicle, transverse process, and rib together form a 3D structural unit, and that screws inserted into this pedicle-rib unit are not inferior to transpedicular screws in terms of stability [18-21].

With respect to pullout strength, this study used screw diameter and length as surrogate markers and evaluated screw-related problems at the 2-year follow-up as outcome measures. Biomechanical studies suggest that larger screw diameters and greater medial convergence may enhance pullout strength and allow the use of longer screws [23]. In this study, L-JET group showed significantly larger diameter of screw than that of the conventional group, which may accomplish positive effect to pullout strength. Regarding screw length, both groups did not show statistical significance. The reason is not short screw in L-JET, but long screw in conventional group. Mean length of screws for thoracic spine was 44.6 mm in the conventional group and 43.9 mm in the L-JET group, which is substantially long screw. A previous paper of 854 pedicle screws reported that mean length was 35–40 mm, 30–35 mm, and 25–30 mm in lower thoracic, middle thoracic and upper thoracic areas, respectively [24]. This finding was attributed to the frequent use of a bicortical screw placement technique in the conventional group.

The L-jet technique is technically simple and reasonable for thoracic pedicular screw placement. This technique utilizes a single consistent entry point and trajectory; thus, memorizing level-specific variable entry points or attempting to identify the entire superior articular facet border to determine its midline as required in conventional techniques is unnecessary [1,10]. Although many studies described the sagittal trajectory as straightforward, few provide guidance regarding the axial trajectory as named as medial convergence [2,9]. Some free-hand techniques for the thoracic pedicle screw insisted that a uniform entry and a fixed medial convergence angle of 20° for transpedicular screw insertion from T3 to T12 [2,11]. Because significant anatomical variation in transverse pedicle across thoracic levels, inserting a transpedicular screw with a single, uniform medial convergence angle is practically unfeasible. Surgeons may either use a small diameter screw or accept a higher risk of cortical breach. Considering the anatomical variability of the thoracic spine, a practically reasonable utilizing a uniform entry point and trajectory is to enter at the L-point and follow a juxtapedicular path. This consistent approach facilitates easier teaching, learning, and procedural standardization in the thoracic spine, particularly in compromised pedicles in patients with spinal tumors.

When placing pedicle screws in patients with spinal tumors, some specific factors need to be considered: (1) the potential for tumor involvement into the pedicle, which may render transpedicular screw placement difficult or compromise pullout strength; (2) inserting the screws as far from the spinal cord as possible to avoid interference with future radiation therapy planning and treatment; and (3) ensuring sufficient pullout strength because metastatic involvement often compromises bone quality. Our rationale for selecting patients with spinal tumors was the high likelihood of pedicle compromise, which often makes transpedicular screw insertion challenging and reduces the biomechanical advantages over extrapedicular screws. Therefore, these findings cannot be generalized to patients with degenerative conditions in whom the pedicles are intact; we cannot assert that this technique is superior to conventional methods in such cases. For patients with pedicle involvement of the tumor, the L-JET technique, using a juxtapedicular path with larger-diameter screws, may serve as an effective alternative. A potential future direction would be to investigate the L-JET technique in nonmalignant thoracic spine conditions, where longer survivorship may allow more comprehensive assessment of long-term fixation durability, including loosening and failure rates.

This study has several limitations that should be acknowledged. First, the study's retrospective, single-center design may introduce selection bias and limit generalizability. Additionally, while the sample size was sufficient for preliminary comparison, it may be underpowered to detect small but clinically significant differences in complication rates or long-term fixation outcomes. Second, although the study was designed for a minimum 2-year follow-up, the mean follow-up period was 13 months, as long-term analysis was limited by the survivorship of metastatic patients. Radiographic complications were rare, suggesting the L-JET technique may not be inferior to conventional methods in fixation durability, though these findings are preliminary due to the low event rate. Third, the evaluation of pullout strength of screw was based on parameters previously established in the literature, including medial convergence, screw diameter, screw length, and cortical breach. The individual contributions of these parameters have been well-established; however, due to uncertainty regarding their relative effects, we only conducted a qualitative evaluation. Future biomechanical studies are needed to objectively quantify these effects. Finally, although operative time and blood loss are important surgical parameters, we were unable to measure the time and bleeding attributable to each individual screw insertion. In particular, differences in case selection, underlying pathology, and extent of decompression or reconstruction may have contributed to the observed variations. Moreover, the number of instrumented levels varied widely among patients, and total operative time and blood loss are strongly influenced by the overall fixation length. For this reason, it is difficult to meaningfully interpret these parameters on a per-screw basis.

Larger multicenter studies are needed to generalize these findings across broader populations and surgical teams. Taken together, these results indicate that the L-point juxtapedicular screw technique offers advantages in terms of uniform entry and trajectory, without increasing complication rates. The technique may be particularly useful in cases with narrow pedicles or pedicle lysis, where conventional transpedicular insertion is limited or risky.

The L-JET technique may be an easy and safe alternative to conventional transpedicular screw insertion in thoracic spinal fixation. It facilitates consistent screw placement using larger-diameter screws, even in compromised pedicles, without increasing complication or revision rates. These findings support its clinical utility; however, further studies are necessary to validate its long-term outcomes.