Biomechanical performance of bicortical versus pericortical bone trajectory (CBT) pedicle screws

Abstract

Purpose The cortical bone trajectory (CBT) is an alternative to the traditional pedicle screw trajectory (TT) in posterior spinal instrumentation, enhancing screw contact with cortical bone and therefore increasing fixation strength. Additional to the trajectory, insertion depth (pericortical vs. bicortical placement) could be a relevant factor affecting the fixation strength. However, the potential biomechanical benefit of a bicortical placement of CBT screws is unknown. Therefore, the aim of this study was to quantify the fixation strength of pericortical-versus bicortical-CBT (pCBT versus bCBT) screws in a randomized cadaveric study. Methods Pedicle screws were either placed pericortical or bicortical with a CBT in 20 lumbar vertebrae (2 × 20 instrumented pedicles) from four human spine cadavers by using patient-specific templates. Instrumented specimens underwent physiological cyclic loading testing (1′800′000 cycles, 10 Hz), including shear and tension loads as well as bending moments. Translational and angular displacements of the screws were quantified and compared between the two techniques. Results There was a slight decrease in translational (0.2 mm ± 0.09 vs. 0.24 mm ± 0.11) and angular displacements (0.06° ± 0.05 vs. 0.13° ± 0.11) of bCBT screws when compared with pCBT screws after 1′800′000 cycles. However, the results were non-significant (p > 0.05). Conclusion The authors do not recommend placing CBT screws bicortically, as no relevant biomechanical advantage is gained while the potential risk for iatrogenic injury to structures anterior to the spine is increased.

The treatment efficacy of cortical bone trajectory (CBT) pedicle screws for lumbar degenerative disease in the Chinese Han population

“…The risk of screw loosening is particularly high in patients with osteoporosis because an inferior reduction of intravertebral screws presents a great challenge for spine surgeons. Jose et al ( 39 ) believed that CBT screws can improve the fixation strength of patients with osteoporosis. Thus, we suggested that the indications of CBT screw included severe osteoporosis, pedicle dysplasia, thin pedicle, and repeated screw placement caused pedicle rupture.…”

Application of the cortical bone trajectory technique in posterior lumbar fixation

“…Although penetrating the sacral endplate seems dangerous, it produces more stability against pullout forces and loosening[ 90 ]. However, Spirig et al [ 91 ] did not recommend placing CBT screws that penetrate the lumbar vertebral endplate, as no relevant biomechanical advantage is gained, while the potential risk for iatrogenic injury to structures anterior to the spine is increased.…”

Editorial: Innovations to improve screw fixation in traumatology and orthopedic surgery

“…If fusion fails, eventually all spinal instrumentation either loosens or breaks. The spine cycles several million times a year, and the loads applied to the instrumentation and its fixation are highly variable (Spirig et al, 2021). They also depend on the construct design (anchor density (Widmer et al, 2020), anchor rigidity (Cornaz et al, 2021;Cornaz et al, 2022) use or absence of anterior column support (Burkhard et al, 2021), which could influence the outcomes and affect the risks of mechanical complications such as fixation loosening, material breakage, and adding on problems such as proximal junctional kyphosis or proximal junctional failure.…”