Biomechanical Evaluation of Cortical Bone Trajectory Fixation with Traditional Pedicle Screw in the Lumbar Spine: A Finite Element Study

Cortical bone trajectory (CBT) is increasingly used in spinal surgery. Although there are many biomechanical studies, the biomechanical effect of CBT in combination with traditional pedicle screws is not detailed. Therefore, the purpose of this study was to investigate the effects of the traditional pedicle screw and CBT screw implantation on the lumbar spine using finite element methods. Based on the combination of the traditional pedicle screw and the CBT system implanted into the lumbar spine, four finite element spinal lumbar models were established. The models were given four different load conditions (flexion, extension, lateral bending, and axial rotation), and the deformation and stress distribution on the finite element model were observed. The results show that there was no significant difference in the structural stability of the lumbar spine model between the traditional pedicle screw system and the CBT system. In addition, CBT may reduce stress on the endplate. Different movements performed by the model may have significant biomechanical effects on the spine and screw system. Clinical spinal surgeons may also consider using the CBT system in revision spinal surgery, which may contribute to smaller wounds.

Comparison of Surgical Outcomes between Cortical Bone Trajectory and Conventional Pedicle Screw Trajectory for Lumbar Degenerative Spondylolisthesis (systematic review of literature)

Background Pedicle screw fixation the gold standard for lumbar spine stabilization. Pedicle screw has fixation offers multiple advantages, allowing superior correction of spinal deformities, and reduced rates of loss of non-union. Cortical Bone Trajectory (CBT) is a new technique in which screws follow a caudal-to-cephalad path in the sagittal plane and a medial-to-lateral directed path in the transverse plane. CBT is reducing operative and post-operative complications and has high fixation strength. Purpose To Compare the clinical outcomes between CBT and traditional trajectory (TT) in surgical management of degenerative spondylolisthesis. Materials and Methods A comprehensive electronic search in Pubmed, MEDLINE and Chocrane library databases, Google scholar and Research gate for articles that published between 2009 to 2020 using these keywords: Cortical bone trajectory, Cortical bone trajectory-pedicle screw, Pedicle screw. Results The majority of literature suggests that the CBT technique results in similar or decreased postoperative back and leg pain compared to TT. Regarding the disability ODI and the operative time showed no significant differences between the CBT and TT. Radiographic outcomes between both studies show no statistical difference in fusion rates and vertebral slippage. Intraoperative blood loss was significantly less with CBT compared to TT. Conclusion there is no widely accepted consensus regarding comparison of clinical outcomes and complications between the CBT and TT procedures. Generally, indications for CBT and TT are similar between most studies, especially for common pathologies resulting in spondylolisthesis.

Incidence of Screw Loosening in Cortical Bone Trajectory Fixation Technique between Single- and Dual-Threaded Screws

Purpose: This study aims to elucidate the radiological outcome after Cortical bone trajectory (CBT) screw fixation and whether dual-threaded (DT) screws should be used in the fusion surgery. Methods: 159 patients with degenerative lumbar disorder who had undergone midline lumbar inter-body fusion surgery by CBT screw-fixation technique (2014 to 2018). Patient subgroups were based on single-threaded (ST) or DT screw, fixation length, as well as whether fixation involved to sacrum level (S1). Serial dynamic plain films were reviewed and an appearance of a halo phenomenon between screw–bone interfaces was identified as a case of screw loosening. Results: 29 patients (39.7%) in ST group and 10 patients (11.6%) in DT group demonstrated a halo phenomenon (p < 0.0001 ****). After subgrouping with fixation length, the incidence rates of a halo phenomenon in each group were 11.1%:3% (ST-1L vs. DT-1L), 37%:13.8% (ST-2L vs. DT-2L), and 84.2%:23.5% (ST-3L vs. DT-3L). Among the 85 patients with a fixation involved in S1, 26 patients (52%) with single-threaded screw (STS group) and 8 patients (22.8%) with dual-threaded screw (DTS group) demonstrated a halo appearance (p = 0.0078 **). After subgrouping the fixation level, the incidence of a halo appearance in each group was 25%:0% (STS-1L vs. DTS-1L), 40.9%:26.3% (STS-2L vs. DTS-2L), and 87.5%: 30% (STS-3L vs. DTS-3L). Conclusion: Both fixation length and whether fixation involved to S1 contribute to the incidence of screw loosening, the data supports clinical evidence that DT screws had greater fixation strength with an increased fixative stability and lower incidence of screw loosening in CBT screw fixation compared with ST screws. Level of evidence: 2.