Should we use cortical bone screws for cortical bone trajectory?

OBJECT In 2009, Santoni et al. reported cortical bone trajectory (CBT) as a method of inserting pedicle screws to obtain more solid fixation, and proposed the use of cortical trajectory screws with a more closely placed thread (cortical screws) for CBT. Since the entry trajectory in CBT differs from that in the traditional trajectory, it is unclear whether the increased strength derives from the specific trajectory or the shape of the screw thread in contact with the cortical bone. Whether the use of cortical screws is always required with CBT thus remains unclear. The authors therefore investigated the relationship between screw entry trajectory and screw thread characteristics and pullout strength in animal experiments. METHODS Lumbar vertebrae (L1–L4) from 4-month-old female pigs were randomly assigned to one of 4 groups, with cancellous screws or cortical screws inserted via the traditional trajectory or CBT. For pullout strength testing, the screw was pulled out vertically against the direction of insertion. Rod pullout testing (toggle testing) was also performed, and the peak breaking strength was measured. RESULTS The maximum pullout strength was significantly greater for CBT using cortical screws than for the traditional trajectory using cancellous screws. Pullout strength tended to be higher when cortical screws were used in both CBT and the traditional trajectory, although the difference was not significant. Toggle testing showed no significant differences among the 4 groups. CONCLUSIONS The specific unconventional trajectory seemed to have a major impact on the increased strength obtained with CBT.

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Biomechanical evaluation of lumbar pedicle screws in spondylolytic vertebrae: comparison of fixation strength between the traditional trajectory and a cortical bone trajectory

Journal of Neurosurgery Spine ◽

10.3171/2015.11.spine15926 ◽

2016 ◽

Vol 24 (6) ◽

pp. 910-915 ◽

Cited By ~ 19

Author(s):

Keitaro Matsukawa ◽

Yoshiyuki Yato ◽

Hideaki Imabayashi ◽

Naobumi Hosogane ◽

Takashi Asazuma ◽

...

Keyword(s):

Cortical Bone ◽

Pedicle Screws ◽

Axial Rotation ◽

Fixation Strength ◽

Isthmic Spondylolisthesis ◽

Pullout Strength ◽

Lateral Bending ◽

Cortical Bone Trajectory ◽

Significant Difference ◽

Flexion Extension

OBJECTIVE In the management of isthmic spondylolisthesis, the pedicle screw system is widely accepted surgical strategy; however, there are few reports on the biomechanical behavior of pedicle screws in spondylolytic vertebrae. The purpose of the present study was to compare fixation strength between pedicle screws inserted through the traditional trajectory (TT) and those inserted through a cortical bone trajectory (CBT) in spondylolytic vertebrae by computational simulation. METHODS Finite element models of spondylolytic and normal vertebrae were created from CT scans of 17 patients with adult isthmic spondylolisthesis (mean age 54.6 years, 10 men and 7 women). Each vertebral model was implanted with pedicle screws using TT and CBT techniques and compared between two groups. First, fixation strength of a single screw was evaluated by measuring axial pullout strength. Next, vertebral fixation strength of a paired-screw construct was examined by applying forces simulating flexion, extension, lateral bending, and axial rotation to vertebrae. RESULTS Fixation strengths of TT screws showed a nonsignificant difference between the spondylolytic and the normal vertebrae (p = 0.31–0.81). Fixation strength of CBT screws in the spondylolytic vertebrae demonstrated a statistically significant decrease in pullout strength (21.4%, p < 0.01), flexion (44.1%, p < 0.01), extension (40.9%, p < 0.01), lateral bending (38.3%, p < 0.01), and axial rotation (28.1%, p < 0.05) compared with those in the normal vertebrae. In the spondylolytic vertebrae, no statistically significant difference was observed for pullout strength between TT and CBT (p = 0.90); however, the CBT construct showed lower vertebral fixation strength in flexion (39.0%, p < 0.01), extension (35.6%, p < 0.01), lateral bending (50.7%, p < 0.01), and axial rotation (59.3%, p < 0.01) compared with the TT construct. CONCLUSIONS CBT screws are less optimal for stabilizing the spondylolytic vertebra due to their lower fixation strength compared with TT screws.

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Surgical Invasiveness of Single-Segment Posterior Lumbar Interbody Fusion: Comparing Perioperative Blood Loss in Posterior Lumbar Interbody Fusion with Traditional Pedicle Screws, Cortical Bone Trajectory Screws, and Percutaneous Pedicle Screws

Asian Spine Journal ◽

10.31616/asj.2020.0296 ◽

2020 ◽

Author(s):

Tetsuji Inoue ◽

Masaya Mizutamari ◽

Kuniaki Hatake

Keyword(s):

Blood Loss ◽

Cortical Bone ◽

Interbody Fusion ◽

Pedicle Screws ◽

Posterior Lumbar Interbody Fusion ◽

Lumbar Interbody Fusion ◽

Cortical Bone Trajectory ◽

Single Segment ◽

Perioperative Blood Loss

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Fixation Strength of Caudal Pedicle Screws after Posterior Lumbar Interbody Fusion with the Modified Cortical Bone Trajectory Screw Method

Asian Spine Journal ◽

10.4184/asj.2016.10.4.639 ◽

2016 ◽

Vol 10 (4) ◽

pp. 639 ◽

Cited By ~ 5

Author(s):

Hironobu Sakaura ◽

Toshitada Miwa ◽

Tomoya Yamashita ◽

Yusuke Kuroda ◽

Tetsuo Ohwada

Keyword(s):

Cortical Bone ◽

Interbody Fusion ◽

Pedicle Screws ◽

Posterior Lumbar Interbody Fusion ◽

Fixation Strength ◽

Lumbar Interbody Fusion ◽

Cortical Bone Trajectory

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Feasibility and safety of using thoracic and lumbar cortical bone trajectory pedicle screws in spinal constructs in children: technical note

Journal of Neurosurgery Pediatrics ◽

10.3171/2017.7.peds17240 ◽

2018 ◽

Vol 21 (2) ◽

pp. 190-196 ◽

Cited By ~ 3

Author(s):

Jonathan N. Sellin ◽

Jeffrey S. Raskin ◽

Kristen A. Staggers ◽

Alison Brayton ◽

Valentina Briceño ◽

...

Keyword(s):

Cortical Bone ◽

Pedicle Screw ◽

Spine Surgery ◽

Intraoperative Complications ◽

Thoracolumbar Spine ◽

Pedicle Screws ◽

Instrumented Fusion ◽

Cortical Bone Trajectory ◽

Estimated Blood Loss ◽

Posterior Instrumented Fusion

Thoracic and lumbar cortical bone trajectory pedicle screws have been described in adult spine surgery. They have likewise been described in pediatric CT-based morphometric studies; however, clinical experience in the pediatric age group is limited. The authors here describe the use of cortical bone trajectory pedicle screws in posterior instrumented spinal fusions from the upper thoracic to the lumbar spine in 12 children. This dedicated study represents the initial use of cortical screws in pediatric spine surgery.The authors retrospectively reviewed the demographics and procedural data of patients who had undergone posterior instrumented fusion using thoracic, lumbar, and sacral cortical screws in children for the following indications: spondylolysis and/or spondylolisthesis (5 patients), unstable thoracolumbar spine trauma (3 patients), scoliosis (2 patients), and tumor (2 patients).Twelve pediatric patients, ranging in age from 11 to 18 years (mean 15.4 years), underwent posterior instrumented fusion. Seventy-six cortical bone trajectory pedicle screws were placed. There were 33 thoracic screws and 43 lumbar screws. Patients underwent surgery between April 29, 2015, and February 1, 2016. Seven (70%) of 10 patients with available imaging achieved a solid fusion, as assessed by CT. Mean follow-up time was 16.8 months (range 13–22 months). There were no intraoperative complications directly related to the cortical bone trajectory screws. One patient required hardware revision for caudal instrumentation failure and screw-head fracture at 3 months after surgery.Mean surgical time was 277 minutes (range 120–542 minutes). Nine of the 12 patients received either a 12- or 24-mg dose of recombinant human bone morphogenic protein 2. Average estimated blood loss was 283 ml (range 25–1100 ml).In our preliminary experience, the cortical bone trajectory pedicle screw technique seems to be a reasonable alternative to the traditional trajectory pedicle screw placement in children. Cortical screws seem to offer satisfactory clinical and radiographic outcomes, with a low complication profile.

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Balancing Rigidity and Safety of Pedicle Screw Fixation via a Novel Expansion Mechanism in a Severely Osteoporotic Model

BioMed Research International ◽

10.1155/2015/318405 ◽

2015 ◽

Vol 2015 ◽

pp. 1-11 ◽

Cited By ~ 2

Author(s):

Thomas M. Shea ◽

James J. Doulgeris ◽

Sabrina A. Gonzalez-Blohm ◽

William E. Lee ◽

Kamran Aghayev ◽

...

Keyword(s):

Cortical Bone ◽

Pedicle Screw ◽

Pedicle Screws ◽

Pedicle Screw Fixation ◽

Cortical Layer ◽

Fixation Strength ◽

Osteoporotic Bone ◽

Pullout Strength ◽

Initial Fixation ◽

Increased Risk

Many successful attempts to increase pullout strength of pedicle screws in osteoporotic bone have been accompanied with an increased risk of catastrophic damage to the patient. To avoid this, a single-armed expansive pedicle screw was designed to increase fixation strength while controlling postfailure damage away from the nerves surrounding the pedicle. The screw was then subsequently tested in two severely osteoporotic models: one representing trabecular bone (with and without the presence of polymethylmethacrylate) and the other representing a combination of trabecular and cortical bone. Maximum pullout strength, stiffness, energy to failure, energy to removal, and size of the resulting block damage were statistically compared among conditions. While expandable pedicle screws produced maximum pullout forces less than or comparable to standard screws, they required a higher amount of energy to be fully removed from both models. Furthermore, damage to the cortical layer in the composite test blocks was smaller in all measured directions for tests involving expandable pedicle screws than those involving standard pedicle screws. This indicates that while initial fixation may not differ in the presence of cortical bone, the expandable pedicle screw offers an increased level of postfailure stability and safety to patients awaiting revision surgery.

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

Applied Sciences ◽

10.3390/app112210583 ◽

2021 ◽

Vol 11 (22) ◽

pp. 10583

Author(s):

Kuo-Chih Su ◽

Kun-Hui Chen ◽

Chien-Chou Pan ◽

Cheng-Hung Lee

Keyword(s):

Finite Element ◽

Lumbar Spine ◽

Cortical Bone ◽

Pedicle Screw ◽

Spinal Surgery ◽

Pedicle Screws ◽

Element Model ◽

Cortical Bone Trajectory ◽

Significant Difference ◽

Flexion Extension

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.

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Fixation Strength of Pedicle and Cortical Lumbar Vertebral Screws after Laminectomy: A Cadaver Study

Journal of Neurological Surgery Part A Central European Neurosurgery ◽

10.1055/s-0038-1639333 ◽

2018 ◽

Vol 79 (04) ◽

pp. 273-278

Author(s):

Dai-Soon Kwak ◽

Ho-Jung Cho ◽

Ho Chang ◽

Moon Park ◽

In-Sung Kim ◽

...

Keyword(s):

Lumbar Vertebrae ◽

Pedicle Screws ◽

Cadaver Study ◽

Fixation Strength ◽

Pullout Strength ◽

Screw Insertion ◽

Cortical Screw ◽

Significant Difference ◽

Midline Approach ◽

Biomechanical Strength

Background and Study Aim Cortical screws were proposed as an alternative to the traditional pedicle screws. Diverse experimental results support the biomechanical superiority of cortical screws compared to pedicle screws. Laminectomy is often part of multilevel lumbar surgeries. Laminectomy might weaken the medial bony edge at the entry of the divergently oriented screw and, thereby, the screw purchase. This study investigated the biomechanical strength of lumbar cortical screw after laminectomy. Objective To compare the fixation strength of cortical screws and traditional pedicle screws after lumbar laminectomy. Material and Methods A total of 120 pedicles from 60 lumbar vertebrae of 12 cadavers (8 men, 4 women) were assessed. The mean age of the cadavers was 73.4 ± 6.2 years (range: 62–82 years). Using a posterior midline approach, we inserted the traditional pedicle screws into one and the cortical screws into the other side of each vertebra. Laminectomy was performed after screw insertion. Vertical pullout strength and toggle strength testing were performed to compare the fixation strength between the two sides. Results After laminectomy, the pullout strength of the cortical screws was 718.92 ± 340.76 N, and that of the pedicle screws was 625.78 ± 287.10 N (p = 0.183). The toggle strength of the cortical screws was 544.83 ± 329.97 N; that of the pedicle screws was 613.17 ± 311.70 N (p = 0.145). No significant difference was found in biomechanical strength between the two types of screws. Conclusion Despite laminectomy, lumbar cortical screws offers comparable pullout and toggle biomechanical strength as traditional pedicle screws.

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