scholarly journals Monoaxial Pedicle Screws Are Superior to Polyaxial Pedicle Screws and the Two Pin External Fixator for Subcutaneous Anterior Pelvic Fixation in a Biomechanical Analysis

2013 ◽  
Vol 2013 ◽  
pp. 1-6 ◽  
Author(s):  
Rahul Vaidya ◽  
Ndidi Onwudiwe ◽  
Matthew Roth ◽  
Anil Sethi
Keyword(s):  
Pedicle Screw ◽  
External Fixator ◽  
Pedicle Screws ◽  
Peak Torque ◽  
Biomechanical Analysis ◽  
Torsional Stiffness ◽  
Pelvic Fixation ◽  
Elastic Range ◽  
Torsional Testing ◽  
Polyaxial Screws

Purpose. Comparison of monoaxial and polyaxial screws with the use of subcutaneous anterior pelvic fixation.Methods. Four different groups each having 5 constructs were tested in distraction within the elastic range. Once that was completed, 3 components were tested in torsion within the elastic range, 2 to torsional failure and 3 in distraction until failure.Results. The pedicle screw systems showed higher stiffness (4.008 ± 0.113 Nmm monoaxial, 3.638 ± 0.108 Nmm Click-x; 3.634 ± 0.147 Nmm Pangea) than the exfix system (2.882 ± 0.054 Nmm) in distraction. In failure testing, monoaxial pedicle screw system was stronger (360 N) than exfixes (160 N) and polyaxial devices which failed if distracted greater than 4 cm (157 N Click-x or 138 N Pangea). The exfix had higher peak torque and torsional stiffness than all pedicle systems. In torsion, the yield strengths were the same for all constructs.Conclusion. The infix device constructed with polyaxial or monoaxial pedicle screws is stiffer than the 2 pin external fixator in distraction testing. In extreme cases, the use of reinforcement or monoaxial systems which do not fail even at 360 N is a better option. In torsional testing, the 2 pin external fixator is stiffer than the pedicle screw systems.

scholarly journals Evaluation of the Effect of Fixation Angle between Polyaxial Pedicle Screw Head and Rod on the Failure of Screw-Rod Connection

2015 ◽  
Vol 2015 ◽  
pp. 1-9 ◽  
Author(s):  
Engin Çetin ◽  
Mustafa Özkaya ◽  
Ümit Özgür Güler ◽  
Emre Acaroğlu ◽  
Teyfik Demir
Keyword(s):  
Mechanical Properties ◽  
Pedicle Screw ◽  
Pedicle Screws ◽  
Maximum Load ◽  
Test Results ◽  
Screw Head ◽  
Pull Out ◽  
Flexion Moment ◽  
Polyaxial Screws ◽  
Different Diameters

Introduction.Polyaxial screws had been only tested according to the ASTM standards (when they were perpendicularly positioned to the rod). In this study, effects of the pedicle screws angled fixation to the rod on the mechanical properties of fixation were investigated.Materials and Method.30 vertically fixed screws and 30 screws fixed with angle were used in the study. Screws were used in three different diameters which were 6.5 mm, 7.0 mm, and 7.5 mm, in equal numbers. Axial pull-out and flexion moment tests were performed. Test results compared with each other using appropriate statistical methods.Results.In pull-out test, vertically fixed screws, in 6.5 mm and 7.0 mm diameter, had significantly higher maximum load values than angled fixed screws with the same diameters (P<0.01). Additionally, vertically fixed screws, in all diameters, had significantly greater stiffness according to corresponding size fixed with angle (P<0.005).Conclusion.Fixing the pedicle screw to the rod with angle significantly decreased the pull-out stiffness in all diameters. Similarly, pedicle screw instrumentation fixed with angle decreased the minimum sagittal angle between the rod and the screw in all diameters for flexion moment test but the differences were not significant.

Biomechanical analysis in a human cadaveric model of spinous process fixation with an interlaminar allograft spacer for lumbar spinal stenosis

2012 ◽  
Vol 16 (6) ◽  
pp. 585-593 ◽  
Author(s):  
Ben B. Pradhan ◽  
Alexander W. L. Turner ◽  
Michael A. Zatushevsky ◽  
G. Bryan Cornwall ◽  
Sean S. Rajaee ◽  
...  
Keyword(s):  
Pedicle Screw ◽  
Screw Fixation ◽  
Spinous Process ◽  
Pedicle Screws ◽  
Axial Rotation ◽  
Pedicle Screw Fixation ◽  
Biomechanical Analysis ◽  
Instrumented Fusion ◽  
Lumbar Spinal ◽  
Flexion And Extension

Object Traditional posterior pedicle screw fixation is well established as the standard for spinal stabilization following posterior or posterolateral lumbar fusion. In patients with lumbar spinal stenosis requiring segmental posterior instrumented fusion and decompression, interlaminar lumbar instrumented fusion (ILIF) is a potentially less invasive alternative with reduced morbidity and includes direct decompression assisted by an interlaminar allograft spacer stabilized by a spinous process plate. To date, there has been no biomechanical study on this technique. In the present study the biomechanical properties of the ILIF construct were evaluated using an in vitro cadaveric biomechanical analysis, and the results are presented in comparison with other posterior fixation techniques. Methods Eight L1–5 cadaveric specimens were subjected to nondestructive multidirectional testing. After testing the intact spine, the following conditions were evaluated at L3–4: bilateral pedicle screws, bilateral laminotomy, ILIF, partial laminectomy, partial laminectomy plus unilateral pedicle screws, and partial laminectomy plus bilateral screws. Intervertebral motions were measured at the index and adjacent levels. Results Bilateral pedicle screws without any destabilization provided the most rigid construct. In flexion and extension, ILIF resulted in significantly less motion than the intact spine (p < 0.05) and no significant difference from the laminectomy with bilateral pedicle screws (p = 0.76). In lateral bending, there was no statistical difference between ILIF and laminectomy with unilateral pedicle screws (p = 0.11); however, the bilateral screw constructs were more rigid (p < 0.05). Under axial rotation, ILIF was not statistically different from laminectomy with unilateral or bilateral pedicle screws or from the intact spine (p > 0.05). Intervertebral motions adjacent to ILIF were typically lower than those adjacent to laminectomy with bilateral pedicle screws. Conclusions Stability of the ILIF construct was not statistically different from bilateral pedicle screw fixation following laminectomy in the flexion and extension and axial rotation directions, while adjacent segment motions were decreased. The ILIF construct may allow surgeons to perform a minimally invasive, single-approach posterior decompression and instrumented fusion without the added morbidity of traditional pedicle screw fixation and posterolateral fusion.

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.

scholarly journals Machine Learning-Based Diagnosis in Laser Resonance Frequency Analysis for Implant Stability of Orthopedic Pedicle Screws

Sensors ◽  
2021 ◽  
Vol 21 (22) ◽  
pp. 7553
Author(s):  
Katsuhiro Mikami ◽  
Mitsutaka Nemoto ◽  
Takeo Nagura ◽  
Masaya Nakamura ◽  
Morio Matsumoto ◽  
...  
Keyword(s):  
Machine Learning ◽  
Resonance Frequency ◽  
Frequency Analysis ◽  
Pedicle Screws ◽  
Peak Torque ◽  
Resonance Frequency Analysis ◽  
Implant Stability ◽  
Laser Resonance ◽  
Analysis Scheme ◽  
Polyaxial Screws

Evaluation of the initial stability of implants is essential to reduce the number of implant failures of pedicle screws after orthopedic surgeries. Laser resonance frequency analysis (L-RFA) has been recently proposed as a viable diagnostic scheme in this regard. In a previous study, L-RFA was used to demonstrate the diagnosis of implant stability of monoaxial screws with a fixed head. However, polyaxial screws with movable heads are also frequently used in practice. In this paper, we clarify the characteristics of the laser-induced vibrational spectra of polyaxial screws which are required for making L-RFA diagnoses of implant stability. In addition, a novel analysis scheme of a vibrational spectrum using L-RFA based on machine learning is demonstrated and proposed. The proposed machine learning-based diagnosis method demonstrates a highly accurate prediction of implant stability (peak torque) for polyaxial pedicle screws. This achievement will contribute an important analytical method for implant stability diagnosis using L-RFA for implants with moving parts and shapes used in various clinical situations.

scholarly journals Biomechanical Analysis of Cortical Versus Pedicle Screw Fixation Stability in TLIF, PLIF, and XLIF Applications

2018 ◽  
Vol 9 (2) ◽  
pp. 162-168 ◽  
Author(s):  
Edward K. Nomoto ◽  
Guy R. Fogel ◽  
Alexandre Rasouli ◽  
Justin V. Bundy ◽  
Alexander W. Turner
Keyword(s):  
Pedicle Screw ◽  
Interbody Fusion ◽  
Screw Fixation ◽  
Pedicle Screws ◽  
Axial Rotation ◽  
Biomechanical Analysis ◽  
Lumbar Interbody Fusion ◽  
Lateral Bending ◽  
Cortical Screw ◽  
Flexion Extension

Study Design: Cadaveric biomechanical study. Objectives: Medial-to-lateral trajectory cortical screws are of clinical interest due to the ability to place them through a less disruptive, medialized exposure compared with conventional pedicle screws. In this study, cortical and pedicle screw trajectory stability was investigated in single-level transforaminal lumbar interbody fusion (TLIF), posterior lumbar interbody fusion (PLIF), and extreme lateral interbody fusion (XLIF) constructs. Methods: Eight lumbar spinal units were used for each interbody/screw trajectory combination. The following constructs were tested: TLIF + unilateral facetectomy (UF) + bilateral pedicle screws (BPS), TLIF + UF + bilateral cortical screws (BCS), PLIF + medial facetectomy (MF) + BPS, PLIF + bilateral facetectomy (BF) + BPS, PLIF + MF + BCS, PLIF + BF + BCS, XLIF + BPS, XLIF + BCS, and XLIF + bilateral laminotomy + BCS. Range of motion (ROM) in flexion-extension, lateral bending, and axial rotation was assessed using pure moments. Results: All instrumented constructs were significantly more rigid than intact ( P < .05) in all test directions except TLIF + UF + BCS, PLIF + MF + BCS, and PLIF + BF + BCS in axial rotation. In general, XLIF and PLIF + MF constructs were more rigid (lowest ROM) than TLIF + UF and PLIF + BF constructs. In the presence of substantial iatrogenic destabilization (TLIF + UF and PLIF + BF), cortical screw constructs tended to be less rigid (higher ROM) than the same pedicle screw constructs in lateral bending and axial rotation; however, no statistically significant differences were found when comparing pedicle and cortical fixation for the same interbody procedures. Conclusions: Both cortical and pedicle trajectory screw fixation provided stability to the 1-level interbody constructs. Constructs with the least iatrogenic destabilization were most rigid. The more destabilized constructs showed less lateral bending and axial rotation rigidity with cortical screws compared with pedicle screws. Further investigation is warranted to understand the clinical implications of differences between constructs.

scholarly journals Cortical screws used to rescue failed lumbar pedicle screw construct: a biomechanical analysis

2015 ◽  
Vol 22 (2) ◽  
pp. 166-172 ◽  
Author(s):  
Graham C. Calvert ◽  
Brandon D. Lawrence ◽  
Amir M. Abtahi ◽  
Kent N. Bachus ◽  
Darrel S. Brodke
Keyword(s):  
Lumbar Spine ◽  
Pedicle Screw ◽  
Pedicle Screws ◽  
Axial Rotation ◽  
The Other ◽  
Biomechanical Analysis ◽  
Pullout Strength ◽  
Lateral Bending ◽  
Cortical Screw ◽  
Flexion Extension

OBJECT Cortical trajectory screw constructs, developed as an alternative to pedicle screw fixation for the lumbar spine, have similar in vitro biomechanics. The possibility of one screw path having the ability to rescue the other in a revision scenario holds promise but has not been evaluated. The objective in this study was to investigate the biomechanical properties of traditional pedicle screws and cortical trajectory screws when each was used to rescue the other in the setting of revision. METHODS Ten fresh-frozen human lumbar spines were instrumented at L3–4, 5 with cortical trajectory screws and 5 with pedicle screws. Construct stiffness was recorded in flexion/extension, lateral bending, and axial rotation. The L-3 screw pullout strength was tested to failure for each specimen and salvaged with screws of the opposite trajectory. Mechanical stiffness was again recorded. The hybrid rescue trajectory screws at L-3 were then tested to failure. RESULTS Cortical screws, when used in a rescue construct, provided stiffness in flexion/extension and axial rotation similar to that provided by the initial pedicle screw construct prior to failure. The rescue pedicle screws provided stiffness similar to that provided by the primary cortical screw construct in flexion/extension, lateral bending, and axial rotation. In pullout testing, cortical rescue screws retained 60% of the original pedicle screw pullout strength, whereas pedicle rescue screws retained 65% of the original cortical screw pullout strength. CONCLUSIONS Cortical trajectory screws, previously studied as a primary mode of fixation, may also be used as a rescue option in the setting of a failed or compromised pedicle screw construct in the lumbar spine. Likewise, a standard pedicle screw construct may rescue a compromised cortical screw track. Cortical and pedicle screws each retain adequate construct stiffness and pullout strength when used for revision at the same level.

The effect of screw head design on rod derotation in the correction of thoracolumbar spinal deformity

2013 ◽  
Vol 19 (3) ◽  
pp. 351-359 ◽  
Author(s):  
Fred C. Lam ◽  
Michael W. Groff ◽  
Ron N. Alkalay
Keyword(s):  
Degrees Of Freedom ◽  
Thoracolumbar Spine ◽  
Pedicle Screws ◽  
Torsional Stiffness ◽  
Screw Head ◽  
Screw Design ◽  
Spine Model ◽  
Polyaxial Screws ◽  
Fixed Axis ◽  
Whole Spine

Object The use of fixed-axis pedicle screws for correction of thoracolumbar deformity in adult surgery is demanding because of the challenge of assembling the bent rod to the screw in order to achieve curve correction. Polyaxial screw designs, providing increased degrees of freedom at the screw-rod interface, were reported to be insufficient in achieving correction of thoracic deformity in the axial plane. Using a multisegment bovine calf spine model, this study investigated the ability of a new uniplanar screw design to achieve derotation correction of the vertebrae and maintain a degree of correction comparable to that of fixed-axis and polyaxial screw designs. Methods Eighteen calf thoracolumbar spine segments from T-6 to L-1 (n = 6 per screw design) underwent bilateral facetectomies at the T9–11 levels and were instrumented bilaterally with pedicle screws and rods. To assess the efficacy of each screw design in imparting rotational correction, each instrumented level was tested under applied torsional moments designed to simulate the motion applied during derotation surgery. Once rotation was achieved, the whole spine was tested to assess the overall stiffness of the construct. Results The fixed-axis construct showed increased efficacy in imparting rotation compared with the uniplanar (115% increase, p > 0.05) and polyaxial (210% increase, p < 0.05) constructs. Uniplanar screws showed a 21% increase in torsional stiffness compared with the polyaxial screws, but this difference was not statistically significant. Conclusions The design of screw heads plays a significant role in affecting the rotation of the vertebrae during the derotation procedure. Uniplanar screws may have the advantage of maintaining construct stiffness after derotation.

Image-Guided Spinal Surgery and Robotics in MIS: Where Are We Now?

2018 ◽  
Vol 1 (2) ◽  
pp. 2
Author(s):  
Chiung Chyi Shen
Keyword(s):  
Pedicle Screw ◽  
Spinal Surgery ◽  
Surgical Navigation ◽  
Improve Patient Safety ◽  
Intraoperative Imaging ◽  
Spinal Instrumentation ◽  
Pedicle Screws ◽  
Computer Assisted ◽  
Navigation Systems ◽  
Image Guided

Use of pedicle screws is widespread in spinal surgery for degenerative, traumatic, and oncological diseases. The conventional technique is based on the recognition of anatomic landmarks, preparation and palpation of cortices of the pedicle under control of an intraoperative C-arm (iC-arm) fluoroscopy. With these conventional methods, the median pedicle screw accuracy ranges from 86.7% to 93.8%, even if perforation rates range from 21.1% to 39.8%.The development of novel intraoperative navigational techniques, commonly referred to as image-guided surgery (IGS), provide simultaneous and multiplanar views of spinal anatomy. IGS technology can increase the accuracy of spinal instrumentation procedures and improve patient safety. These systems, such as fluoroscopy-based image guidance ("virtual fluoroscopy") and computed tomography (CT)-based computer-guidance systems, have sensibly minimized risk of pedicle screw misplacement, with overall perforation rates ranging from between 14.3% and 9.3%, respectively."Virtual fluoroscopy" allows simultaneous two-dimensional (2D) guidance in multiple planes, but does not provide any axial images; quality of images is directly dependent on the resolution of the acquired fluoroscopic projections. Furthermore, computer-assisted surgical navigation systems decrease the reliance on intraoperative imaging, thus reducing the use of intraprocedure ionizing radiation. The major limitation of this technique is related to the variation of the position of the patient from the preoperative CT scan, usually obtained before surgery in a supine position, and the operative position (prone). The next technological evolution is the use of an intraoperative CT (iCT) scan, which would allow us to solve the position-dependent changes, granting a higher accuracy in the navigation system. 

Augmented reality–assisted pedicle screw insertion: a cadaveric proof-of-concept study

2019 ◽  
Vol 31 (1) ◽  
pp. 139-146 ◽  
Author(s):  
Camilo A. Molina ◽  
Nicholas Theodore ◽  
A. Karim Ahmed ◽  
Erick M. Westbroek ◽  
Yigal Mirovsky ◽  
...  
Keyword(s):  
Augmented Reality ◽  
Pedicle Screw ◽  
User Experience ◽  
Pedicle Screws ◽  
Screw Insertion ◽  
Pedicle Screw Insertion ◽  
Insertion Method ◽  
Comparative Accuracy ◽  
Placement Accuracy ◽  
Surgical Field

OBJECTIVEAugmented reality (AR) is a novel technology that has the potential to increase the technical feasibility, accuracy, and safety of conventional manual and robotic computer-navigated pedicle insertion methods. Visual data are directly projected to the operator’s retina and overlaid onto the surgical field, thereby removing the requirement to shift attention to a remote display. The objective of this study was to assess the comparative accuracy of AR-assisted pedicle screw insertion in comparison to conventional pedicle screw insertion methods.METHODSFive cadaveric male torsos were instrumented bilaterally from T6 to L5 for a total of 120 inserted pedicle screws. Postprocedural CT scans were obtained, and screw insertion accuracy was graded by 2 independent neuroradiologists using both the Gertzbein scale (GS) and a combination of that scale and the Heary classification, referred to in this paper as the Heary-Gertzbein scale (HGS). Non-inferiority analysis was performed, comparing the accuracy to freehand, manual computer-navigated, and robotics-assisted computer-navigated insertion accuracy rates reported in the literature. User experience analysis was conducted via a user experience questionnaire filled out by operators after the procedures.RESULTSThe overall screw placement accuracy achieved with the AR system was 96.7% based on the HGS and 94.6% based on the GS. Insertion accuracy was non-inferior to accuracy reported for manual computer-navigated pedicle insertion based on both the GS and the HGS scores. When compared to accuracy reported for robotics-assisted computer-navigated insertion, accuracy achieved with the AR system was found to be non-inferior when assessed with the GS, but superior when assessed with the HGS. Last, accuracy results achieved with the AR system were found to be superior to results obtained with freehand insertion based on both the HGS and the GS scores. Accuracy results were not found to be inferior in any comparison. User experience analysis yielded “excellent” usability classification.CONCLUSIONSAR-assisted pedicle screw insertion is a technically feasible and accurate insertion method.

scholarly journals Minimally Invasive Techniques for Iliac Bolt Placement: 2-Dimensional Operative Video

2021 ◽  
Vol 20 (4) ◽  
pp. E292-E292
Author(s):  
Travis Hamilton ◽  
Mohamed Macki ◽  
Thomas M Zervos ◽  
Victor Chang
Keyword(s):  
Minimally Invasive ◽  
Imaging System ◽  
Pedicle Screws ◽  
Vertical Axis ◽  
Spinal Diseases ◽  
Open Approach ◽  
Sagittal Vertical Axis ◽  
Pelvic Fixation ◽  
Iliac Screws ◽  
Invasive Techniques

Abstract As the popularity of minimally invasive surgery (MIS) continues to grow, novel techniques are needed to meet the demands of multisegment fixation for advanced spinal diseases. In one such example, iliac bolts are often required to anchor large fusion constructs, but MIS technical notes are missing from the literature.  A 67-yr-old female presented with a symptomatic coronal deformity: preoperative pelvic incidence = 47°, pelvic tilt = 19°, and lumbar lordosis = 29°, sagittal vertical axis = +5.4 cm with 30° of scoliosis. The operative plan included T10-ilium fusion with transforaminal interbody grafts at L2-3, L3-4, L4-5, and L5-S1. The intraoperative video is of minimally invasive placement of iliac bolts using the O-Arm Surgical Imaging System (Medtronic®). The patient consented to the procedure.  A mini-open exposure that remains above the fascial planes allows for multilevel instrumentation with appropriate decompression at the interbody segments. After the placement of the pedicle screws under image-guidance, the direction is turned to the minimally invasive iliac bolts. Following the trajectory described in the standard open approach,1 the posterior superior iliac spine (PSIS) is identified with the navigation probe, which will guide the Bovie cautery through the fascia. This opening assists in the trajectory of the navigated-awl tap toward the anterior superior iliac spine (ASIS). Next, 8.5 mm x 90 mm iliac screws were placed in the cannulated bone under navigation. After intraoperative image confirmation of screw placement, the contoured rods are threaded under the fascia. The setscrews lock the rod in position. MIS approaches obviate cross-linking the rods, rendering pelvic fixation more facile.  This technique allows for minimal dissection of the posterior pelvic soft tissue while maintaining adequate fixation.

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