Biomechanical evaluation of fixation strength among different sizes of pedicle screws using the cortical bone trajectory: what is the ideal screw size for optimal fixation?

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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Biomechanical evaluation of the fixation strength of lumbar pedicle screws using cortical bone trajectory: a finite element study

Journal of Neurosurgery Spine ◽

10.3171/2015.1.spine141103 ◽

2015 ◽

Vol 23 (4) ◽

pp. 471-478 ◽

Cited By ~ 32

Author(s):

Keitaro Matsukawa ◽

Yoshiyuki Yato ◽

Hideaki Imabayashi ◽

Naobumi Hosogane ◽

Takashi Asazuma ◽

...

Keyword(s):

Finite Element ◽

Cortical Bone ◽

Pedicle Screws ◽

Axial Rotation ◽

Fixation Strength ◽

Lateral Bending ◽

Cortical Bone Trajectory ◽

Flexion Extension ◽

Flexion And Extension ◽

Multidirectional Loading

OBJECT Cortical bone trajectory (CBT) maximizes thread contact with the cortical bone surface and provides increased fixation strength. Even though the superior stability of axial screw fixation has been demonstrated, little is known about the biomechanical stiffness against multidirectional loading or its characteristics within a unit construct. The purpose of the present study was to quantitatively evaluate the anchorage performance of CBT by the finite element (FE) method. METHODS Thirty FE models of L-4 vertebrae from human spines (mean age [± SD] 60.9 ± 18.7 years, 14 men and 16 women) were computationally created and pedicle screws were placed using the traditional trajectory (TT) and CBT. The TT screw was 6.5 mm in diameter and 40 mm in length, and the CBT screw was 5.5 mm in diameter and 35 mm in length. To make a valid comparison, the same shape of screw was inserted into the same pedicle in each subject. First, the fixation strength of a single pedicle screw was compared by axial pullout and multidirectional loading tests. Next, vertebral fixation strength within a construct was examined by simulating the motions of flexion, extension, lateral bending, and axial rotation. RESULTS CBT demonstrated a 26.4% greater mean pullout strength (POS; p = 0.003) than TT, and also showed a mean 27.8% stronger stiffness (p < 0.05) during cephalocaudal loading and 140.2% stronger stiffness (p < 0.001) during mediolateral loading. The CBT construct had superior resistance to flexion and extension loading and inferior resistance to lateral bending and axial rotation. The vertebral fixation strength of the construct was significantly correlated with bone mineral density of the femoral neck and the POS of a single screw. CONCLUSIONS CBT demonstrated superior fixation strength for each individual screw and sufficient stiffness in flexion and extension within a construct. The TT construct was superior to the CBT construct during lateral bending and axial rotation.

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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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Comparison of Three Different Screw Trajectories in Osteoporotic Vertebrae: A Biomechanical Investigation

10.21203/rs.3.rs-78150/v1 ◽

2020 ◽

Author(s):

Jan-Sven Jarvers ◽

Stefan Schleifenbaum ◽

Christian Pfeifle ◽

Christoph Oefner ◽

Melanie Edel ◽

...

Keyword(s):

Cortical Bone ◽

Fatigue Behavior ◽

Fixation Strength ◽

Patient Specific ◽

Promising Alternative ◽

Cortical Bone Trajectory ◽

Pull Out ◽

Group A ◽

The Mean ◽

Group B

Abstract Background: Pedicle screw insertion in osteoporotic patients is challenging. Achieving more screw-cortical bone purchase and invasiveness minimization, the cortical bone trajectory and the midline cortical techniques represent alternatives to traditional pedicle screws. This study compares the fatigue behavior and fixation strength of the cement-augmented traditional trajectory (TT), the cortical bone trajectory (CBT) and the midline cortical (MC). Methods: Ten human cadaveric spine specimens (L1 - L5) were examined. The average age was 86.3 ± 7.2 years. CT scans were provided for preoperative planning. CBT and MC were implanted by using the patient-specific 3D-printed placement guide (MySpine®, Medacta International), TT were implanted freehand. All 10 cadaveric specimens were randomized to group A (CBT vs. MC) or group B (MC vs. TT). Each screw was loaded for 10,000 cycles. The failure criterion was doubling of the initial screw displacement resulting from the compressive force (60 N) at the first cycle, the stop criterion as a doubling of the initial screw displacement. After dynamic testing, screws were pulled out axially at 5 mm/min to determine their remaining fixation strength. Results: The mean pull-out forces did not differ significantly. Concerning the fatigue performance, only one out of ten MC of group A failed prematurely due to loosening after 1,500 cycles (L3). Five CBT already loosened during the first 500 cycles. The mean displacement was always lower in the MC. In group B, all TT showed no signs of failure or loosening. Three MC failed already after 26 cycles, 1,510 cycles, and 2,144 cycles, respectively. The TT showed always a lower mean displacement. In the subsequent pull-out tests, the remaining mean fixation strength of the MC (449.6 ± 298.9 N) was slightly higher compared to the mean pull-out force of the CBT (401.2 ± 261.4 N). However, MC (714.5 ± 488.0 N) were inferior to TT (990.2 ± 451.9 N).Conclusion: The current study demonstrated that cement-augmented TT have best fatigue and pull-out characteristics in osteoporotic lumbar vertebrae, followed by the MC and CBT. MC represent a promising alternative in osteoporotic bone if cement augmentation should be avoided. Using the patient-specific guide contributes to improve screws’ biomechanical properties.

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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 Cross Trajectory Technique for Pedicle Screw Insertion: Combined Use of Traditional Trajectory and Cortical Bone Trajectory

Orthopaedic Surgery ◽

10.1111/os.12212 ◽

2015 ◽

Vol 7 (4) ◽

pp. 317-323 ◽

Cited By ~ 5

Author(s):

Keitaro Matsukawa ◽

Yoshiyuki Yato ◽

Hideaki Imabayashi ◽

Naobumi Hosogane ◽

Takashi Asazuma ◽

...

Keyword(s):

Cortical Bone ◽

Pedicle Screw ◽

Cortical Bone Trajectory ◽

Screw Insertion ◽

Pedicle Screw Insertion ◽

Combined Use ◽

Biomechanical Evaluation

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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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