scholarly journals Evaluation of the Intrinsic Properties of Pedicle Screws: Do Diameter, Manufacturing and Screw Design Affect Resistance and/or Resistivity

2009 ◽  
Vol 9 (1) ◽  
pp. S77-S82 ◽  
Author(s):  
Worawat Limthongkul ◽  
Jason Savage ◽  
Emmanuel K. Nenonene ◽  
Eldin E. Karaikovic
Keyword(s):  
Pedicle Screw ◽  
Pedicle Screws ◽  
Constant Current ◽  
Intrinsic Properties ◽  
Measurement Variability ◽  
Screw Design ◽  
Measured Voltage ◽  
Lower Resistance ◽  
Screw Diameter ◽  
Lower Resistivity

The pedicle screw diameter, composite and design are variables that can affect the threshold of intraoperative electromyographic monitoring. Even though we know that larger diameter objects tend to have less resistance, no study documented the effect that this variable could have on pedicle screw resistance. Using high quality equipment, resistance and resistivity of ten pedicle screws (from four manufacturers) were calculated based on known constant current and measured voltage. Voltage was measured three times for each screw to determine intraobserver measurement variability. Resistance of all screws ranged from 1.4 to 3.9 m ohm (mean = 2.69+/-0.71 m ohm). The screw with largest diameter (7.75 mm) had lower resistance than screws with other diameters. Resistivity of screws ranged from 7.12 to 12.63 micro ohm*m (mean = 9.9+/-1.82 micro ohm*m). Based on the screw design, one manufacturer's pedicle screws (A) had significantly lower resistivity compared to three other manufacturers (p<0.01). Larger diameter screws (7.75 mm in diameter) had lower resistance. Screw design (polyaxial or monoaxial) had no effect on its resistance. Screws of one manufacturer (A) showed lower resistivity compared to those manufactured by other three companies.

scholarly journals Evaluation of C2 pedicle screw placement via the freehand technique by neurosurgical trainees

2018 ◽  
Vol 29 (3) ◽  
pp. 235-240 ◽  
Author(s):  
Martin H. Pham ◽  
Joshua Bakhsheshian ◽  
Patrick C. Reid ◽  
Ian A. Buchanan ◽  
Vance L. Fredrickson ◽  
...  
Keyword(s):  
Pedicle Screw ◽  
Medical Center ◽  
Pedicle Screws ◽  
Screw Placement ◽  
Pedicle Screw Placement ◽  
C2 Pedicle Screw ◽  
Canal Diameter ◽  
Screw Length ◽  
Freehand Technique ◽  
Screw Diameter

OBJECTIVEFreehand placement of C2 instrumentation is technically challenging and has a learning curve due the unique anatomy of the region. This study evaluated the accuracy of C2 pedicle screws placed via the freehand technique by neurosurgical resident trainees.METHODSThe authors retrospectively reviewed all patients treated at the LAC+USC Medical Center undergoing C2 pedicle screw placement in which the freehand technique was used over a 1-year period, from June 2016 to June 2017; all procedures were performed by neurosurgical residents. Measurements of C2 were obtained from preoperative CT scans, and breach rates were determined from coronal reconstructions on postoperative scans. Severity of breaches reflected the percentage of screw diameter beyond the cortical edge (I = < 25%; II = 26%–50%; III = 51%–75%; IV = 76%–100%).RESULTSNeurosurgical residents placed 40 C2 pedicle screws in 24 consecutively treated patients. All screws were placed by or under the guidance of Pham, who is a postgraduate year 7 (PGY-7) neurosurgical resident with attending staff privileges, with a PGY-2 to PGY-4 resident assistant. The authors found an average axial pedicle diameter of 5.8 mm, axial angle of 43.1°, sagittal angle of 23.0°, spinal canal diameter of 25.1 mm, and axial transverse foramen diameter of 5.9 mm. There were 17 screws placed by PGY-2 residents, 7 screws placed by PGY-4 residents, and 16 screws placed by the PGY-7 resident. The average screw length was 26.0 mm, with a screw diameter of 3.5 mm or 4.0 mm. There were 7 total breaches (17.5%), of which 4 were superior (10.0%) and 3 were lateral (7.5%). There were no medial breaches. The breaches were classified as grade I in 3 cases (42.9%), II in 3 cases (42.9%), III in 1 case (14.3%), and IV in no cases. There were 3 breaches that occurred via placement by a PGY-2 resident, 3 breaches by a PGY-4 resident, and 1 breach by the PGY-7 resident. There were no clinical sequelae due to these breaches.CONCLUSIONSFreehand placement of C2 pedicle screws can be done safely by neurosurgical residents in early training. When breaches occurred, they tended to be superior in location and related to screw length choice, and no breaches were found to be clinically significant. Controlled exposure to this unique anatomy is especially pertinent in the era of work-hour restrictions.

114. Dual thread screw design provides equivalent fixation to upsized screw diameter in revision pedicle screw instrumentation

2020 ◽  
Vol 20 (9) ◽  
pp. S56
Author(s):  
Joseph L. Laratta ◽  
Ryan Weegens ◽  
Jeffrey L. Gum ◽  
Michael J. Voor ◽  
Leah Y. Carreon ◽  
...  
Keyword(s):  
Pedicle Screw ◽  
Pedicle Screw Instrumentation ◽  
Screw Design ◽  
Screw Diameter

Relationship of Height and Weight to Maximum Safe Pedicle Screw Diameter in the Lumbar Spine

2020 ◽  
Author(s):  
Jonathon Lentz ◽  
Joseph Albano ◽  
Robert Stockton ◽  
Maximillian Ganz ◽  
Larry Lutsky ◽  
...  
Keyword(s):  
Lumbar Spine ◽  
Pedicle Screw ◽  
Lumbar Vertebrae ◽  
Pedicle Screws ◽  
Significant Difference ◽  
Operative Planning ◽  
Screw Position ◽  
Screw Diameter ◽  
Intimate Knowledge ◽  
Relationship Of

Abstract Background Safely performing instrumented spinal fusion requires an intimate knowledge of anatomy and variations. Pedicle screw position and size have implications on intraoperative and post-operative complications. While pre-operative planning with Computed Tomography (CT) scan measurements may be the safest way to judge trajectory and maximal screw size, it is not standard practice for many spine surgeons. We investigated how height and weight correlated with PD. We hypothesized that these routinely obtained, non-invasive measurements would provide an easily referenced data point to aid in perioperative estimation of maximum safe pedicle screw diameter (MSPSD).Methods Coronal cuts of the lumbar spine were assessed to obtain transverse outer cortical PD as measured through the isthmus at lumbar vertebrae one through five. We assessed whether height, weight, and BMI significantly correlated with PD in our diverse population. Results Height and weight were found to significantly correlate with PD. Height explained roughly 10% of the variance in PD, weight explained only 3-4%, and BMI nearly 0%. There were significant differences in this theoretical safety profiles between the “Taller Height” and “Shorter Height” groups for the majority of pedicle screw sizes at L1 through L3. Significant differences between the populations at L4 and L5 were only seen for 8.0 mm screws at the L4 level. At L5, 100% of the “Taller Height” and “Shorter Height” subjects’ pedicles could safely accommodate pedicle screws up to 8.0 mm in diameter.Conclusions We previously reported on the significant difference in PD between different races. The results of this study provide yet another variable to be considered when making radiographic assessments of pedicle diameter.

Accuracy of Free-Hand Pedicle Screws in the Thoracic and Lumbar Spine: Analysis of 6816 Consecutive Screws

Neurosurgery ◽  
2011 ◽  
Vol 68 (1) ◽  
pp. 170-178 ◽  
Author(s):  
Scott L. Parker ◽  
Matthew J. McGirt ◽  
S Harrison. Farber ◽  
Anubhav G. Amin ◽  
Anne-Marie. Rick ◽  
...  
Keyword(s):  
Lumbar Spine ◽  
Radiation Exposure ◽  
Pedicle Screw ◽  
Pedicle Screws ◽  
Screw Placement ◽  
Pedicle Screw Placement ◽  
Intraoperative Fluoroscopy ◽  
Thoracic And Lumbar Spine ◽  
Institutional Experience ◽  
Screw Diameter

Abstract BACKGROUND: Pedicle screws are used to stabilize all 3 columns of the spine, but can be technically demanding to place. Although intraoperative fluoroscopy and stereotactic-guided techniques slightly increase placement accuracy, they are also associated with increased radiation exposure to patient and surgeon as well as increased operative time. OBJECTIVE: To describe and critically evaluate our 7-year institutional experience with placement of pedicle screws in the thoracic and lumbar spine using a free-hand technique. METHODS: We retrospectively reviewed records of all patients undergoing free-hand pedicle screw placement without fluoroscopy in the thoracic or lumbar spine between June 2002 and June 2009. Incidence and extent of cortical breach by misplaced pedicle screw was determined by review of postoperative computed tomography scans. We defined breach as more than 25% of the screw diameter residing outside of the pedicle or vertebral body cortex. RESULTS: A total of 964 patients received 6816 free-hand placed pedicle screws in the thoracic or lumbar spine. Indications for hardware placement were degenerative/deformity disease (51.2%), spondylolisthesis (23.7%), tumor (22.7%), trauma (11.3%), infection (7.6%), and congenital (0.9%). A total of 115 screws (1.7%) were identified as breaching the pedicle in 87 patients (9.0%). Breach occurred more frequently in the thoracic than the lumbar spine (2.5% and 0.9%, respectively; P &lt; .0001) and was more often lateral (61.3%) than medial (32.8%) or superior (2.5%). T4 (4.1%) and T6 (4.0%) experienced the highest breach rate, whereas L5 and S1 had the lowest breach rate. Eight patients (0.8%) underwent revision surgery to correct malpositioned screws. CONCLUSION: Free-hand pedicle screw placement based on external anatomy alone can be performed with acceptable safety and accuracy and allows avoidance of radiation exposure encountered in fluoroscopic techniques. Image-guided assistance may be most valuable when placing screws between T4 and T6, where breach rates are highest.

scholarly journals Partial Threading of Pedicle Screws in a Standard Construct Increases Fatigue Life: A Biomechanical Analysis

2021 ◽  
Vol 11 (4) ◽  
pp. 1503
Author(s):  
Fon-Yih Tsuang ◽  
Chia-Hsien Chen ◽  
Lien-Chen Wu ◽  
Yi-Jie Kuo ◽  
Yueh-Ying Hsieh ◽  
...  
Keyword(s):  
Finite Element ◽  
Fatigue Life ◽  
Pedicle Screw ◽  
Pedicle Screws ◽  
Biomechanical Analysis ◽  
Von Mises Stress ◽  
Shaft Length ◽  
Element Analysis ◽  
Screw Design ◽  
Screw Length

This study proposed a pedicle screw design where the proximal 1/3 of the screw is unthreaded to improve fixation in posterior spinal surgery. This design was also expected to reduce the incidence of mechanical failure often observed when an unsupported screw length is exposed outside the vertebra in deformed or degenerated segments. The aim of this study was to evaluate the fatigue life of the novel pedicle screw design using finite element analysis and mechanical testing in a synthetic spinal construct in accordance with American Society for Testing and Materials (ASTM) F1717. The following setups were evaluated: (i) pedicle screw fully inserted into the test block (EXP-FT-01 and EXP-PU-01; full thread (FT), proximal unthread (PU)) and (ii) pedicle screw inserted but leaving an exposed shaft length of 7.6 mm (EXP-FT-02 and EXP-PU-02). Corresponding finite element models FEM-FT-01, FEM-FT-02, FEM-PU-01, and FEM-PU-02 were also constructed and subjected to the same loading conditions as the experimental groups. The results showed that under a 220 N axial load, the EXP-PU-01 group survived the full 5 million cycles, the EXP-PU-02 group failed at 4.4 million cycles on average, and both EXP-FT-01 and EXP-FT-02 groups failed after less than 1.0 million cycles on average, while the fatigue strength of the EXP-FT-02 group was the lowest at 170 N. The EXP-FT-01 and EXP-FT-02 constructs failed through fracture of the pedicle screw, but a rod fractured in the EXP-PU-02 group. In comparison to the FEM-FT-01 model, the maximum von Mises stress on the pedicle screw in the FEM-PU-01 and FEM-PU-02 models decreased by −43% and −27%, respectively. In conclusion, this study showed that having the proximal 1/3 of the pedicle screw unthreaded can reduce the risk of screw fatigue failure when used in deformed or degenerated segments.

Proposal for an Adaptive Bone Screw Design Based on FEA Studies Exemplified by Pedicle Screw

2021 ◽  
Author(s):  
Alexander Seidler ◽  
Lars Mehlhorn ◽  
Philipp Sembdner ◽  
Stefan Holtzhausen ◽  
Ralph Stelzer ◽  
...  
Keyword(s):  
Simulation Model ◽  
Pedicle Screw ◽  
Cancellous Bone ◽  
Adaptive Design ◽  
Pedicle Screws ◽  
Bone Screws ◽  
Design Models ◽  
Bone Screw ◽  
Cad System ◽  
Screw Design

Abstract This paper presents a proposal for a density-adaptive design of bone screws using pedicle screws for spinal fixations as an example. The basis is the analysis and categorization of currently available variants of bone screws, which differ in principle in their thread design because of different application areas (cortical or cancellous bone). These screw variants are investigated in FEA simulations for pullout and bending with regard to occurring stresses. A corresponding simulation model is presented for this purpose. The precise design models for these screws are generated in a CAD system using a self-developed configuration tool. Based on the FEA evaluation, the proposal for a new pedicle screw design, consisting of several thread types merged into each other, is described in detail. By integrating different thread types over the shaft, the respective properties of the bone can thus be optimally utilized.

scholarly journals Alternative Pedicle Screw Design via Biomechanical Evaluation

2020 ◽  
Vol 10 (14) ◽  
pp. 4746 ◽  
Author(s):  
Jiwoon Kwon ◽  
Myung Heon Ha ◽  
Moon Gu Lee
Keyword(s):  
Spinal Fusion ◽  
Pedicle Screw ◽  
Bending Strength ◽  
Pedicle Screws ◽  
The Elderly ◽  
Spinal Diseases ◽  
Fusion Surgery ◽  
Spinal Fusion Surgery ◽  
Screw Design ◽  
Experimental Apparatus

With the recent increase in the elderly population, many people suffer from spinal diseases, and, accordingly, spinal fusion surgery using pedicle screws has been widely applied to treat them. However, most research on pedicle screw design has been focused on the test results rather than the behavior of the screws and vertebrae. In this study, a design platform with a series of biomechanical tests and analyses were presented for pedicle screw improvement and evaluation. The platform was then applied to an alternative hybrid screw design with quadruple and double threads. An experimental apparatus was developed to investigate the bending strength of the screw, and several tests were performed based on the ASTM F1717 standard. In the experiments, it was confirmed that the alternative pedicle screw has the highest bending strength. To examine the stress distribution of pedicle screws, finite element models were established, through which it was found that the proposed pedicle screw has sufficient mechanical safety to make it acceptable for spinal fusion treatment. Finally, we conclude that the platform has good potential for the design and evaluation of pedicle screws, and the alternative dual screw design is one of the best options for spinal fusion surgery.

scholarly journals Comparison of Insertion Time, Pull-out Strength, and Screw-media Interface Area of Customized Pedicle Screw With Different Core and Thread Design Against Commercial Pedicle Screw

2021 ◽  
Author(s):  
Rahadyan Magetsari ◽  
Tedjo Rukmoyo ◽  
Marda Ade Saputra ◽  
Yudha Mathan Sakti
Keyword(s):  
Pedicle Screw ◽  
Pedicle Screws ◽  
Insertion Time ◽  
Control Group ◽  
Interface Area ◽  
Screw Design ◽  
Pull Out ◽  
Thread Diameter ◽  
Screw Group ◽  
Pull Out Strength

Abstract Objective: This research aimed to developing customized pedicle screw based on Indonesian vertebral anatomy and compare the insertion time, pull-out strength, and screw-media interface area of different screw design. We have developed 3 different types of pedicle screws (v-thread cylinder-core, square-thread cylinder-core and square-thread conical-core). The thread diameter was calculated from pedicle width of Indonesian population (6 mm). We used commercially available pedicle screw as control group (6.2 mm). Result: The insertion time were significantly difference between v-thread cylinder-core pedicle screw (22,94 s) with commercially available pedicle screw (15.86 s) (p<0.05). The pull-out strength was significantly difference between commercially available pedicle screw (408.60 N) with square-thread conical pedicle screw (836.60 N) (p<0.05). The square-thread conical-core group have the highest interface area (1486.21 mm2). The data comparison showed that the square-thread conical-core customized pedicle screw group has comparable insertion time and has better pull-out strength than commercially available pedicle screw.

scholarly journals Comparison of insertion time, pull-out strength, and screw-media interface area of customized pedicle screw with different core and thread design against commercial pedicle screw: a pilot study on Indonesian Population

2022 ◽  
Vol 15 (1) ◽  
Author(s):  
Rahadyan Magetsari ◽  
Tedjo Rukmoyo ◽  
Marda Ade Saputra ◽  
Yudha Mathan Sakti
Keyword(s):  
Pedicle Screw ◽  
Pedicle Screws ◽  
Insertion Time ◽  
Control Group ◽  
Interface Area ◽  
Screw Design ◽  
Pull Out ◽  
Indonesian Population ◽  
Thread Diameter ◽  
Pull Out Strength

Abstract Objective This research aimed to developing customized pedicle screw based on Indonesian vertebral anatomy and compare the insertion time, pull-out strength, and screw-media interface area of different screw design. We have developed 3 different types of pedicle screws (v-thread cylinder-core, square-thread cylinder-core and square-thread conical-core). The thread diameter was calculated from pedicle width of Indonesian population (6 mm). We used commercially available pedicle screw as control group (6.2 mm). Result The insertion time were significantly difference between v-thread cylinder-core pedicle screw (22.94 s) with commercially available pedicle screw (15.86 s) (p < 0.05). The pull-out strength was significantly difference between commercially available pedicle screw (408.60 N) with square-thread conical pedicle screw (836.60 N) (p < 0.05). The square-thread conical-core group have the highest interface area (1486.21 mm2). The data comparison showed that the square-thread conical-core customized pedicle screw group has comparable insertion time and has better pull-out strength than commercially available pedicle screw.

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