The posterior transpedicular internal fixation technique is widely used in the treatment of various degenerative spinal diseases owing to its ability to provide stable three-column spinal fixation [1–4]. However, the wide range of soft tissue dissection, large trauma, and excessive bleeding during the surgical process can easily result in postoperative back pain, infection, and other complications. Patients with developed back muscles or obesity are more likely to experience such issues. Osteoporosis patients frequently experience postoperative screw loosening and removal [5,6].

To address the aforementioned issues, Santoni et al. [7] proposed cortical bone trajectory (CBT) for lumbar pedicle screws in 2009, which increased the screw’s contact with the cortical bone and optimized the screw’s biomechanical properties. The closer the insertion point is to the midline, the less the dissection of the soft tissue in the back muscle. Several published studies show that this technique is a viable alternative to the traditional pedicle screw technique [8,9]. Because it reduces surgical time, soft tissue exposure, and blood loss; improves biomechanical stability; and allows for faster patient recovery, cortical trajectory screw fixation has been widely used in the treatment of various degenerative lumbar diseases [10–12].

As an emerging surgical technique, CBT remains controversial in terms of preoperative evaluation methods, key surgical techniques, complication prevention and treatment, postoperative follow-up, and other aspects, resulting in unclear indications and contraindications for some doctors and posing great challenges for its steady promotion [13–15]. Currently, there is no expert consensus on the application of CBT. The modified Delphi method is an anonymous approach of gathering expert opinions via multiple rounds of face-to-face surveys and systematically designed questionnaires [16]. The goal of this study was to determine the consensus of experts on the use of CBT for lumbar pedicle screws using the modified Delphi method.

Of the 81 panelists invited, 74 participated, with responses from 72, 70, and 69 for each survey (Table 1). Consensus was reached on 24 questions, including 59 options, following the Delphi rounds. Grade A consensus was reached in 35.6% of options, grade B in 37.3%, and grade C in 27.1%.

Tables 2–4 summarized grade A, B, and C recommendations as well as the percentage of agreement with the summary of CBT, which included indications and contraindications, advantages and disadvantages, preoperative evaluation, complications, and postoperative follow-up evaluation, among other things.

The research team searched several Chinese and English databases, and the majority of the consensus points were supported by evidence-based studies.

In this consensus, indications of CBT include lumbar disc herniation or lumbar spinal stenosis with osteoporosis (it can also be used for normal bone density); 1° or 2° lumbar spondylolisthesis; degenerative scoliosis with Cobb angle less than 20°; adjacent segmental diseases (ASD) after lumbar internal fixation; multi-anchor fixation (cortical bone screw satellite rod technique); screw placement after lumbar bone cement implantation (vertebroplasty); and remedial measures after failure of traditional pedicle screw placement. Contraindications of CBT include lumbar spondylolisthesis of 3° or higher, isthmic spondylolisthesis, previous surgery or bone-destroying diseases that result in bone destruction or absence in the lamina or isthmus, and degenerative scoliosis with more than 2° rotation.

They were consistent with the published literature. Zhang et al. [18] performed a large-scale comparative meta-analysis and found that both cortical bone screws and traditional screws could produce good results after lumbar interbody fusion. The Visual Analog Scale score of postoperative back and leg pain, Japanese Orthopaedic Association score, and interbody fusion rate did not significantly vary between the two groups of patients. However, in the cortical bone screw fixation group, the duration of surgery, intraoperative blood loss, length of hospital stay, incidence of postoperative complications, adjacent segmental degeneration, incidence of ASD, and Oswestry Disability Index were significantly lower than those for traditional pedicle screw fixation. Chang et al. [19] reviewed and analyzed the research progress of CBT in the surgical treatment of lumbar spondylolisthesis and discovered that CBT was superior to pedicle screws in terms of surgical bleeding, surgical duration, the incidence of intraoperative complications, postoperative adjacent segment degeneration, and revision surgery owing to degeneration at a 1-year follow-up. Menon et al. [15] also revealed that the CBT screw technique for lumbar spinal stenosis and grade 1 lumbar spondylolisthesis could provide comparable results. Hussain et al. [20] also found that CBT screws had similar clinical effects to traditional pedicle screws in the treatment of lumbar spondylolisthesis after a 1-year follow-up. Chen et al. [21] used CBT screw technology to treat six patients with postoperative adjacent vertebral diseases of the lumbar spine without removing the original internal fixation devices during the operation, with a short incision, small exposure area, less blood loss and soft tissue injury, and satisfactory postoperative outcomes. Ueno et al. [22] used the dual-track technique to treat a patient with degenerative lumbar scoliosis and severe osteoporosis. They used cortical bone screws as well as pedicle screws. Follow-up 14 months after surgery revealed that the patient had good postoperative internal fixation with no corrective loss.

The CBT screw track crosses four bone cortices: the dorsal entry point, the medial posterior wall of the pedicle, the lateral anterior wall of the pedicle, and the vertebral body. The nail track has a larger contact area with cortical bone, which improves biomechanical stability, pull-out force, and control force [23,24]. It provides significant benefits to patients with osteoporosis. CBT screw technology is closer to the insertion point, reducing dissection of the back muscle soft tissue. This can greatly reduce the difficulty of surgery and postoperative pain in patients with muscular backs or obesity. Several published studies have confirmed that the CBT screw technique leads to smaller surgical incisions, shorter operative times, less blood loss, faster patient recovery, and improved postoperative outcomes [11,24,25]. Orita et al. [26] proposed percutaneous cutaneous bone trajectory to make the wound less invasive. With the advancement of The Times and the use of robots and navigation, CBT screw technology can become more precise and minimally invasive, lowering surgical trauma and postoperative complications [27]. Han et al. [28] discovered in a 3-year follow-up study that compared to traditional pedicle screw internal fixation and fusion technology, single-segment cortical screw internal fixation effectively reduces the occurrence of postoperative degeneration of adjacent segments.

However, although CBT screw technology reduces the surgical incision, it makes the operation more difficult. Because of the smaller incision and limited exposure range during the operation, it is common to have difficulty identifying the anatomical structure of the vertebral body and determining the intraoperative screw placement path. Improper screw placement may result in nerve injury [29]. Simultaneously, due to the screw’s limited direction and exposure range, connecting the screw rod when fixing the long segment of the lumbar spine is often difficult.

CBT technique necessitates high accuracy in nail placement path, so precise surgical operation is one of the keys to surgical success. Matsukawa et al. [30] conducted morphological studies and determined that the ideal insertion point for CBT was outside the pedicle isthmus, at the intersection of the superior articular process’s midline and the 1-mm horizontal line below the lower edge of the transverse process. Gao et al. [31] discovered that for CBT screw placement channels, the maximum screw length gradually increased from 32.0 to 35.3 mm from L1 to L4 before decreasing to 34.8 mm in L5. A CBT screw length of 30 mm was considered safe for the Chinese lumbar spine. The diameter of the thickest screw grew gradually from 4.5 mm in L1 to 7.5 mm in L5. CBT screws with diameters of 4.0 mm in L1 to L2 and 4.5 mm in L3 to L5 are recommended. The CBT screw placement and sagittal angles are 10°–16° and 25°–30°, respectively. CBT screws and traditional pedicle screws can be modified in osteoporotic lumbar vertebrae, with each screw retaining adequate torque, pull-out strength, and fatigue resistance. The biomechanical stability of conventional pedicle screws with modified CBT was comparable to that of the initial pedicle screws, but it decreased significantly when compared to that of the original CBT screws. The screw path of the original pedicle screw greatly influences the screw path of the modified CBT screw. However, the track of the original CBT screw had little influence on the track of the traditional pedicle revision screw.

When using an unfamiliar surgical approach and performing an unskilled operation, the risk of accidental injury and postoperative complications increases significantly. The learning curve and potential complications should be considered when performing CBT.

Petrone et al. [25] investigated 238 patients with lumbar degenerative diseases who underwent CBT and discovered that the overall postoperative complication rate was 4.2%. The most common complications were improper screw placement and surgical incision infection, followed by fusion device displacement and neurological issues. Preoperative CT for surgical path planning and intraoperative three-dimensional printed guide plates can significantly reduce the number of complications associated with internal fixation. Lee et al. [8] investigated early postoperative complications of CBT and discovered that complications related to internal fixation were as high as 29.4%, with internal fixation loosening and fusion device displacement being the most prevalent. Incorrect screw placement and osteoporosis are the most common causes of complications with internal fixation. The intraoperative exposure range is reduced when compared to traditional pedicle screws, which may result in inaccurate anatomical understanding and displacement of the insertion point for surgeons who are new to using CBT screw technology.

The modified Delphi method is widely used for gathering expert opinions via multiple rounds of face-to-face surveys and systematically designed questionnaires. In the Delphi survey, the selection of panelists is critical to achieving expert consensus. Improper selection of experts will increase bias in the investigation and reduce the response rate in the consultation process.

In this study, panelists were chosen from the authoritative academic organization of the CSSLS, and all met the selection criteria, which were well represented in terms of age and medical practice. During the expert evaluation process, the questionnaire recovery rate exceeded 90%, and a large proportion of experts proposed changes.

There are also some limitations to this study: (1) Because all of the selected panelists are from China, the expert consensus is not applicable to other countries or regions. (2) There is a lack of statistical analyses in the Delphi rounds. The absence of statistical methods such as the Likert scale and content validity ratio in the Delphi study may have reduced the precision and reliability of our findings. Despite these limitations, our study sheds light on the clinical application of CBT for lumbar pedicle screws and establishes a foundational expert consensus. Moving forward, addressing these methodological considerations will strengthen and broaden the applicability of the research.

By establishing clear guidelines for the use of CBT, the study enables clinicians to make informed decisions about patient selection, which is critical for improving outcomes and avoiding complications. The consensus on key surgical techniques and best practices can assist surgeons in effectively implementing CBT, potentially improving patient safety. Recommendations for preoperative evaluation and postoperative follow-up provide practical advice to improve patient care and recovery. Identifying common complications and management strategies aids in anticipating and mitigating potential problems, ultimately improving treatment outcomes. While expert consensus provides a foundational understanding, these findings are intended to fill gaps in clinical practice and direct future research. We believe that these recommendations will improve the use of CBT in lumbar pedicle screw surgery and lead to better patient outcomes.

The modified Delphi method was used to establish expert consensus to inform clinical decision-making regarding the use of CBT. CBT is a minimally invasive, effective, and safe treatment for many degenerative lumbar disorders. The best indications for CBT are lumbar disc herniation or lumbar spinal stenosis with osteoporosis; 1° or 2° lumbar spondylolisthesis; degenerative scoliosis with Cobb angle less than 20°; ASD; multi-anchor fixation; screw placement after lumbar bone cement implantation; and remedial measures after traditional pedicle screw failure.