1
|
Steinmetz MP, Riggleman JR, Mahoney JM, Harris JA, Butler JB, Ferrick BJ, Bucklen BS. A Dual-Screw Technique for Vertebral Compression Fractures via Robotic Navigation in the Osteopenic Lumbar Spine: An In-Vitro Biomechanical Analysis. Global Spine J 2024; 14:1706-1713. [PMID: 36644787 DOI: 10.1177/21925682231152833] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Indexed: 01/17/2023] Open
Abstract
STUDY DESIGN Biomechanical cadaveric study. OBJECTIVES Multi-rod constructs maximize posterior fixation, but most use a single pedicle screw (PS) anchor point to support multiple rods. Robotic navigation allows for insertion of PS and cortical screw (CS) within the same pedicle, providing 4 points of bony fixation per vertebra. Recent studies demonstrated radiographic feasibility for dual-screw constructs for posterior lumbar spinal fixation; however, biomechanical characterization of this technique is lacking. METHODS Fourteen cadaveric lumbar specimens (L1-L5) were divided into 2 groups (n = 7): PS, and PS + CS. VCF was simulated at L3. Bilateral posterior screws were placed from L2-L4. Load control (±7.5Nm) testing performed in flexion-extension (FE), lateral bending (LB), axial rotation (AR) to measure ROM of: (1) intact; (2) 2-rod construct; (3) 4-rod construct. Static compression testing of 4-rod construct performed at 5 mm/min to measure failure load, axial stiffness. RESULTS Four-rod construct was more rigid than 2-rod in FE (P < .001), LB (P < .001), AR (P < .001). Screw technique had no significant effect on FE (P = .516), LB (P = .477), or AR (P = .452). PS + CS 4-rod construct was significantly more stable than PS group (P = .032). Stiffness of PS + CS group (445.8 ± 79.3 N/mm) was significantly greater (P = .019) than PS (317.8 ± 79.8 N/mm). Similarly, failure load of PS + CS group (1824.9 ± 352.2 N) was significantly greater (P = .001) than PS (913.4 ± 309.8 N). CONCLUSIONS Dual-screw, 4-rod construct may be more stable than traditional rod-to-rod connectors, especially in axial rotation. Axial stiffness and ultimate strength of 4-rod, dual-screw construct were significantly greater than rod-to-rod. In this study, 4-rod construct was found to have potential biomechanical benefits of increased strength, stiffness, stability.
Collapse
Affiliation(s)
- Michael P Steinmetz
- Department of Neurosurgery, Cleveland Clinic Lerner College of Medicine, Center for Spine Health Neurologic Institute, Cleveland Clinic, Cleveland, OH, USA
| | - Jessica R Riggleman
- Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., Audubon, PA, USA
| | - Jonathan M Mahoney
- Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., Audubon, PA, USA
| | - Jonathan A Harris
- Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., Audubon, PA, USA
| | - John B Butler
- Department of Neurosurgery, Cleveland Clinic Lerner College of Medicine, Center for Spine Health Neurologic Institute, Cleveland Clinic, Cleveland, OH, USA
| | - Bryan J Ferrick
- School of Biomedical Engineering, Science and Health Systems, Drexel University, Philadelphia, PA, USA
| | - Brandon S Bucklen
- Musculoskeletal Education and Research Center, A Division of Globus Medical, Inc., Audubon, PA, USA
| |
Collapse
|
2
|
Matheus V, Albert CJ. Robotics-guided placement of second set of screws in one pedicle: A case report. INTERDISCIPLINARY NEUROSURGERY 2022. [DOI: 10.1016/j.inat.2021.101411] [Citation(s) in RCA: 0] [Impact Index Per Article: 0] [Reference Citation Analysis] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 10/19/2022] Open
|
3
|
Tandon V, Franke J, Kalidindi KKV. Advancements in osteoporotic spine fixation. J Clin Orthop Trauma 2020; 11:778-785. [PMID: 32904223 PMCID: PMC7452352 DOI: 10.1016/j.jcot.2020.06.028] [Citation(s) in RCA: 9] [Impact Index Per Article: 2.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/25/2020] [Revised: 06/12/2020] [Accepted: 06/16/2020] [Indexed: 01/01/2023] Open
Abstract
With the global rise in the population of elderly along with other risk factors, spine surgeons have to encounter osteoporotic spine more often. Osteoporotic spine, however, causes problems in management, particularly where instrumentation is involved, resulting in screw loosening, pull out, pseudoarthroses or adjacent segment kyphosis. Osteoporosis alters the bio mechanics at the bone implant interface resulting in various degrees of fixation failure. Various advancements have been made in this field to deal with such issues in addition to modification of basic surgical techniques such as increasing the diameter and length of the screw, smaller pilot hole, under tapping, longer constructs, supplemental anterior fixation, sublaminar wires or laminar hooks, use of transverse connectors and triangulation techniques, among others. They include novel surgical techniques such as cortical bone trajectory, superior cortical trajectory, double screw technique, cross trajectory technique, bicortical screw technique or prophylactic vertebroplasty. Advances in the screw design include expandable screws, fenestrated screws, conical screws and coated screws. In addition to PMMA cement augmentation, other biodegradable cements have been introduced to mitigate the side effects of PMMA such as calcium phosphate, calcium apatite and hydroxyapatite. Pharmacotherapy with teriparatide can aid fusion and lower the rate of pedicle screw loosening. Many of these strategies have only bio mechanical evidence and require well designed clinical trials to establish their clinical efficacy. Though no single technique is fool proof, little modifications in the existing techniques or utilizing a combination of techniques without adding to the cost of the surgery may help to achieve a near-ideal result. Surgeons have to equip their armamentarium with all the recent advances, and should be open to novel thoughts and techniques.
Collapse
Affiliation(s)
- Vikas Tandon
- Department of Spine Service, Indian Spinal Injuries Center, Sector-C, Vasant Kunj, New Delhi, 110070, India,Corresponding author. Sr. Consultant and Unit Head, Department of Spine Service, Indian Spinal Injuries Center, Vasant Kunj, New Delhi, 110070, India.
| | - Jorg Franke
- Department of Orthopedics, Klinikum Magdeburg, Magdeburg, Germany
| | | |
Collapse
|
4
|
Karakasli A, Acar N, Uzun B. Straight-Forward versus Bicortical Fixation Penetrating Endplate in Lumbosacral Fixation-A Biomechanical Study. J Korean Neurosurg Soc 2018. [PMID: 29526060 PMCID: PMC5853203 DOI: 10.3340/jkns.2017.0404.004] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.3] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Download PDF] [Figures] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/28/2022] Open
Abstract
Objective Many lumbosacral fixation techniques have been described to offer a more screw-bone purchase. The forward anatomical fixation parallel to the endplate is still the most preferred method. Literature revealed little knowledge regarding the mechanical stability of lumbosacral trans-endplate fixation compared to the traditional trans-pedicular screw fixation method. The aim of this study is to assess the pull-out strength of lumbosacral screws penetrating the end plate and comparing it to the conventional trans-pedicular screw insertion method. Methods Eight lumbar and eight sacral vertebrae, with average age 69.4 years, Left pedicles of the 5th lumbar vertebrae were used for trans-endplate screw fixation, group 1A, right pedicles were used for anatomical trans-pedicular screw fixation, group 1B. In the sacral vertebrae, the right side S1 pedicles were used for trans-endplate fixation, group 2A, left side pedicles were used for anatomical trans-pedicular screw fixation, group 2B. The biomechanical tests were performed using the axial compression testing machine. All tests were applied using 2 mm/min traction speed. Results The average pull-out strength values of groups 1A and 1B were 403.78±11.71 N and 306.26±17.55 N, respectively. A statistical significance was detected with p=0.012. The average pull-out strength values of groups 2A and 2B were 388.73±17.03 N and 299.84±17.52 N, respectively. A statistical significance was detected with p=0.012. Conclusion The trans-endplate lumbosacral fixation method is a trustable fixation method with a stronger screw-bone purchase and offer a good alternative for surgeons specially in patients with osteoporosis.
Collapse
Affiliation(s)
- Ahmet Karakasli
- Department of Orthopaedics and Traumatology, Dokuz Eylul University, Faculty of Medicine, Izmir, Turkey
| | - Nihat Acar
- Department of Orthopaedics and Traumatology, Catalca Ilyas Cokay Hospital, Istanbul, Turkey
| | - Bora Uzun
- Department of Biomechanics, Dokuz Eylul University, Health Science Institute, Izmir, Turkey
| |
Collapse
|
5
|
Lin HH, Chang MC, Wang ST, Liu CL, Chou PH. The fates of pedicle screws and functional outcomes in a geriatric population following polymethylmethacrylate augmentation fixation for the osteoporotic thoracolumbar and lumbar burst fractures with mean ninety five month follow-up. INTERNATIONAL ORTHOPAEDICS 2018; 42:1313-1320. [DOI: 10.1007/s00264-018-3812-3] [Citation(s) in RCA: 13] [Impact Index Per Article: 2.2] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Received: 11/14/2017] [Accepted: 01/25/2018] [Indexed: 11/30/2022]
|
6
|
Aycan MF, Yaman ME, Usta Y, Demir T, Tolunay T. Investigation of toggling effect on pullout performance of pedicle screws. Proc Inst Mech Eng H 2018; 232:395-402. [DOI: 10.1177/0954411918755417] [Citation(s) in RCA: 9] [Impact Index Per Article: 1.5] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/15/2022]
Abstract
Objective of this study is to assess the pullout performance of various pedicle screws in different test materials after toggling tests comparatively. Solid core, cannulated (cemented), novel expandable and solid-core (cemented) pedicle screws were instrumented to the polyurethane foams (Grade 10 and Grade 40) produced in laboratory and bovine vertebra. ASTM F543 standard was used for preparation process of samples. Toggling tests were carried out. After toggling test procedures, pullout tests were performed. Load versus displacement graph was recorded, and the ultimate pullout force was defined as the maximum load (pullout strength) sustained before failure of screw. Anteriosuperior and oblique radiographs were taken from each sample after instrumentation in order to examine screw placement and cement distribution. The pullout strength of pedicle screws decreased after toggling tests with respect to the initial condition. While the cemented solid-core pedicle screws had the highest pullout strength in all test materials, they had the highest strength differences. The cemented solid-core pedicle screws had decrement rates of 27% and 16% in Grade 10 and Grade 40, respectively. There are almost same decrement rate (between 5.5% and 6.5%) for all types of pedicle screws instrumented to the samples of bovine vertebra. The pullout strengths of novel expandable pedicle screws in both of early period and after toggling conditions were almost similar, in other words, the decrement rates of it were lower than other types. According to the data collected from this study, polymethylmethacrylate augmentation significantly decreases pullout strength following the toggling loads. Higher brittleness of cured polymethylmethacrylate has adverse effect on the pullout strength. Although augmentation is an important process for enhancing pullout strength in early period, it has some disadvantages for preserving stabilization in a long time. Expandable pedicle screw with polyetheretherketone shell may be good alternative to polymethylmethacrylate augmentation on both primer stabilization and long-term loading application with toggling.
Collapse
Affiliation(s)
| | - Mesut Emre Yaman
- Department of Neurosurgery, Memorial Ankara Hospital, Ankara, Turkey
| | - Yusuf Usta
- Department of Mechanical Engineering, Gazi University, Ankara, Turkey
| | - Teyfik Demir
- Department of Mechanical Engineering, TOBB University of Economics and Technology, Ankara, Turkey
| | - Tolga Tolunay
- Department of Orthopedics, Yıldırım Beyazıt University, Ankara, Turkey
| |
Collapse
|
7
|
Aycan MF, Tolunay T, Demir T, Yaman ME, Usta Y. Pullout performance comparison of novel expandable pedicle screw with expandable poly-ether-ether-ketone shells and cement-augmented pedicle screws. Proc Inst Mech Eng H 2017; 231:169-175. [PMID: 28095741 DOI: 10.1177/0954411916687792] [Citation(s) in RCA: 12] [Impact Index Per Article: 1.7] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 11/17/2022]
Abstract
Aim of this study is to assess the pullout performance of various pedicle screws in different test materials. Polyurethane foams (Grade 10 and Grade 40) produced in laboratory and bovine vertebrae were instrumented with normal, cannulated (cemented), novel expandable and normal (cemented) pedicle screws. Test samples were prepared according to the ASTM F543 standard testing protocols and surgical guidelines. To examine the screw placement and cement distribution, anteriosuperior and oblique radiographs were taken from each sample after insertion process was completed. Pullout tests were performed in an Instron 3369 testing device. Load versus displacement graphs were recorded and the ultimate pullout force was defined as the maximum load (pullout strength) sustained before failure of screw. Student's t-test was performed on each group whether the differences between pullout strength of pedicle screws were significant or not. While normal pedicle screws have the lowest pullout strength in all test materials, normal pedicle screws cemented with polymethylmethacrylate exhibit significantly higher pullout performance than others. For all test materials, there is a significant improvement in pullout strength of normal screws by augmentation. While novel expandable pedicle screws with expandable poly-ether-ether-ketone shells exhibited lower pullout performance than normal screws cemented with polymethylmethacrylate, their pullout performances in all groups were higher than the ones of normal and cannulated pedicle screws. For all test materials, although cannulated pedicle screws exhibit higher pullout strength than normal pedicle screws, there are no significant differences between the two groups. The novel expandable pedicle screws with expandable poly-ether-ether-ketone shells may be used instead of normal and cannulated pedicle screws cemented with polymethylmethacrylate due to their good performances.
Collapse
Affiliation(s)
| | - Tolga Tolunay
- 2 Department of Orthopaedics, Ankara Yildirim Beyazit University, Ankara, Turkey
| | - Teyfik Demir
- 3 Department of Mechanical Engineering, TOBB University of Economics and Technology, Ankara, Turkey
| | - Mesut Emre Yaman
- 4 Department of Neurosurgery, Memorial Ankara Hospital, Ankara, Turkey
| | - Yusuf Usta
- 1 Department of Mechanical Engineering, Gazi University, Ankara, Turkey
| |
Collapse
|
8
|
Matsukawa K, Yato Y, Imabayashi H, Hosogane N, Asazuma T, Nemoto K. Biomechanical Evaluation of Cross Trajectory Technique for Pedicle Screw Insertion: Combined Use of Traditional Trajectory and Cortical Bone Trajectory. Orthop Surg 2016; 7:317-23. [PMID: 26792576 DOI: 10.1111/os.12212] [Citation(s) in RCA: 14] [Impact Index Per Article: 1.8] [Reference Citation Analysis] [Abstract] [Key Words] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 09/04/2015] [Accepted: 10/12/2015] [Indexed: 01/16/2023] Open
Abstract
OBJECTIVE To introduce a novel double-screw (cross trajectory) technique that combines use of the traditional trajectory (TT) and cortical bone trajectory (CBT) and to investigate its fixation strength quantitatively by finite element (FE) analysis. METHODS Three-dimensional FE models of 30 osteoporotic L4 vertebrae (patients' mean age: 77.3 ± 7.4 years, 11 men and 19 women) were computationally created. Each vertebral model was implanted with bilateral pedicle screws by TT (using 7.5 mm × 40 mm screws), CBT (using 5.5 mm × 35 mm screws) and cross trajectory (combined use of TT screws of 5.5 mm × 40 mm and CBT screws of 5.5 mm × 35 mm) and compared among three groups. The vertebral fixation strength of a bilateral-screw construct was examined by applying forces simulating flexion, extension, lateral bending, and axial rotation to the vertebrae by non-linear FE analyses. RESULTS Fixation strength using the cross trajectory was the highest among the three different techniques (P < 0.01). The cross trajectory construct demonstrated 320% higher strength than the TT construct in flexion, 293% higher in extension, 102% higher in lateral bending, and 40% higher in axial rotation (P < 0.01). Similarly, the cross trajectory construct showed 268% higher strength than the CBT construct in flexion, 269% higher in extension, 210% higher in lateral bending, and 178% in axial rotation (P < 0.01). CONCLUSIONS The cross trajectory technique offered superior fixation strength over the TT and CBT techniques in each plane of motion. This technique may be a valid option for posterior fusion, especially in osteoporotic spine.
Collapse
Affiliation(s)
- Keitaro Matsukawa
- Department of Orthopaedic Surgery, National Defense Medical College, Tokorozawa, Saitama, Japan
| | - Yoshiyuki Yato
- Department of Orthopaedic Surgery, National Hospital Organization, Murayama Medical Center, Musashimurayama, Tokyo, Japan
| | - Hideaki Imabayashi
- Department of Orthopaedic Surgery, National Defense Medical College, Tokorozawa, Saitama, Japan
| | - Naobumi Hosogane
- Department of Orthopaedic Surgery, National Defense Medical College, Tokorozawa, Saitama, Japan
| | - Takashi Asazuma
- Department of Orthopaedic Surgery, National Hospital Organization, Murayama Medical Center, Musashimurayama, Tokyo, Japan
| | - Koichi Nemoto
- Department of Orthopaedic Surgery, National Defense Medical College, Tokorozawa, Saitama, Japan
| |
Collapse
|
9
|
Goldstein CL, Brodke DS, Choma TJ. Surgical Management of Spinal Conditions in the Elderly Osteoporotic Spine. Neurosurgery 2016; 77 Suppl 4:S98-107. [PMID: 26378363 DOI: 10.1227/neu.0000000000000948] [Citation(s) in RCA: 42] [Impact Index Per Article: 5.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 12/13/2022] Open
Abstract
Osteoporosis, the most common form of metabolic bone disease, leads to alterations in bone structure and density that have been shown to compromise the strength of spinal instrumentation. In addition, osteoporosis may contribute to high rates of fracture and instrumentation failure after long posterior spinal fusions, resulting in proximal junctional kyphosis and recurrent spinal deformity. As increasing numbers of elderly patients present for surgical intervention for degenerative and traumatic spinal pathologies, current and future generations of spine surgeons will increasingly be faced with the challenge of obtaining adequate fixation in osteoporotic bone. The purpose of this review is to familiarize the reader with the impact of osteoporosis on spinal instrumentation, the broad variety of techniques that have been developed for addressing these issues, and the biomechanical and clinical evidence in support of the use of these techniques.
Collapse
Affiliation(s)
- Christina L Goldstein
- *University of Missouri, Department of Orthopaedic Surgery, Columbia, Missouri; ‡Department of Orthopaedic Surgery, University of Utah, Salt Lake City, Utah
| | | | | |
Collapse
|
10
|
Wray S, Mimran R, Vadapalli S, Shetye SS, McGilvray KC, Puttlitz CM. Pedicle screw placement in the lumbar spine: effect of trajectory and screw design on acute biomechanical purchase. J Neurosurg Spine 2015; 22:503-10. [DOI: 10.3171/2014.10.spine14205] [Citation(s) in RCA: 58] [Impact Index Per Article: 6.4] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Subscribe] [Scholar Register] [Indexed: 01/12/2023]
Abstract
OBJECT
Low bone mineral density in patients undergoing lumbar spinal surgery with screws is an especially difficult challenge because poor bone quality can severely compromise the maximum achievable purchase of the screws. A relatively new technique, the cortical bone screw trajectory, utilizes a medialized trajectory in the caudocephalad direction to engage a greater amount of cortical bone within the pars interarticularis and pedicle. The objectives of this cadaveric biomechanical study were to 1) evaluate a cortical screw system and compare its mechanical performance to the traditional pedicle screw system; 2) determine differences in bone quality associated with the cortical screw trajectory versus the normal pedicle screw insertion technique; 3) determine the cortical wall breach rate with both the cortical and traditional screw trajectories; and 4) determine the performance of the traditional screw in the cortical screw trajectory.
METHODS
Fourteen fresh frozen human lumbar spine sections (L1–5) were used in this study (mean age 57 ± 19 years). The experimental plan involved drilling and tapping screw holes for 2 trajectories under navigation (a traditional pedicle screw and a cortical screw) in both high-and low-quality vertebrae, measuring the bone quality associated with these trajectories, placing screws in the trajectories, and evaluating the competence of the screw purchase via 2 mechanical tests (pullout and toggle). The 3 experimental variants were 1) traditional pedicle screws placed in the traditional pedicle screw trajectory, 2) traditional pedicle screws placed in the cortical screw trajectory, and 3) cortical screws placed in the cortical screw trajectory.
RESULTS
A statistically significant increase in bone quality was observed for the cortical trajectories with a cortical screw (42%; p < 0.001) and traditional pedicle screw (48%; p < 0.001) when compared to the traditional trajectory with a traditional pedicle screw within the high-quality bone group. These significant differences were also found in the lowquality bone cohort. All mechanical parameter comparisons (screw type and trajectory) between high-quality and lowquality samples were significant (p < 0.01), and these data were all linearly correlated (r ≥ 0.65) to bone mineral density. Not all mechanical parameters determined from pullout and toggle testing were statistically significant between the 3 screw/trajectory combinations. The incidence of cortical wall breach with the cortical or traditional pedicle screw trajectories was not significantly different.
CONCLUSIONS
The data demonstrated that the cortical trajectory provides denser bone that allows for utilization of smaller screws to obtain mechanical purchase that is equivalent to long pedicle screws placed in traditional pedicle screw trajectories for both normal- and low-quality bone. Overall, this biomechanical study in cadavers provides evidence that the cortical screw trajectory represents a good option to obtain fixation for the lumbar spine with low-quality bone.
Collapse
Affiliation(s)
- Steven Wray
- 1Department of Neurosurgery, Atlanta Brain and Spine Care, Atlanta, Georgia
| | - Ronnie Mimran
- 2Department of Neurological Surgery, Pacific Brain and Spine Medical Group, Danville, California
| | - Sasidhar Vadapalli
- 3Research Engineering, Medtronic Spine and Biologics, Memphis, Tennessee
| | - Snehal S. Shetye
- 4Department of Mechanical Engineering and School of Biomedical Engineering, Colorado State University, Fort Collins, Colorado
| | - Kirk C. McGilvray
- 4Department of Mechanical Engineering and School of Biomedical Engineering, Colorado State University, Fort Collins, Colorado
| | - Christian M. Puttlitz
- 4Department of Mechanical Engineering and School of Biomedical Engineering, Colorado State University, Fort Collins, Colorado
| |
Collapse
|
11
|
Designs and techniques that improve the pullout strength of pedicle screws in osteoporotic vertebrae: current status. BIOMED RESEARCH INTERNATIONAL 2014; 2014:748393. [PMID: 24724097 PMCID: PMC3958762 DOI: 10.1155/2014/748393] [Citation(s) in RCA: 93] [Impact Index Per Article: 9.3] [Reference Citation Analysis] [Abstract] [Track Full Text] [Download PDF] [Figures] [Subscribe] [Scholar Register] [Received: 10/11/2013] [Revised: 01/16/2014] [Accepted: 01/22/2014] [Indexed: 12/21/2022]
Abstract
Osteoporosis is a medical condition affecting men and women of different age groups and populations. The compromised bone quality caused by this disease represents an important challenge when a surgical procedure (e.g., spinal fusion) is needed after failure of conservative treatments. Different pedicle screw designs and instrumentation techniques have been explored to enhance spinal device fixation in bone of compromised quality. These include alterations of screw thread design, optimization of pilot hole size for non-self-tapping screws, modification of the implant's trajectory, and bone cement augmentation. While the true benefits and limitations of any procedure may not be realized until they are observed in a clinical setting, axial pullout tests, due in large part to their reproducibility and ease of execution, are commonly used to estimate the device's effectiveness by quantifying the change in force required to remove the screw from the body. The objective of this investigation is to provide an overview of the different pedicle screw designs and the associated surgical techniques either currently utilized or proposed to improve pullout strength in osteoporotic patients. Mechanical comparisons as well as potential advantages and disadvantages of each consideration are provided herein.
Collapse
|
12
|
Abstract
There are three basic concepts that are important to the biomechanics of pedicle screw-based instrumentation. First, the outer diameter of the screw determines pullout strength, while the inner diameter determines fatigue strength. Secondly, when inserting a pedicle screw, the dorsal cortex of the spine should not be violated and the screws on each side should converge and be of good length. Thirdly, fixation can be augmented in cases of severe osteoporosis or revision. A trajectory parallel or caudal to the superior endplate can minimise breakage of the screw from repeated axial loading. Straight insertion of the pedicle screw in the mid-sagittal plane provides the strongest stability. Rotational stability can be improved by adding transverse connectors. The indications for their use include anterior column instability, and the correction of rotational deformity.
Collapse
Affiliation(s)
- W Cho
- Department of Orthopaedic Surgery, University of Virginia, 114 Old Fifth Circle, Charlottesville, Virginia 22903, USA.
| | | | | |
Collapse
|
13
|
[Degeneration and osteoporosis of the spine. Is there a modified procedure?]. DER ORTHOPADE 2010; 39:425-31. [PMID: 20232196 DOI: 10.1007/s00132-009-1573-9] [Citation(s) in RCA: 2] [Impact Index Per Article: 0.1] [Reference Citation Analysis] [Abstract] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 02/05/2023]
Abstract
Reduced bone quality due to osteoporosis poses a fundamental problem in spine surgery instrumentation. The consequences observed most often are insufficient implant anchoring and adjacent fractures. In cases of manifest osteoporosis, several modern anchoring possibilities are at our disposal that, to differing degrees, increase the stability of the instrumentation. Cement augmentation of a fractured vertebra by means of kyphoplasty or vertebroplasty verifiably leads to significantly better pain reduction than conservative treatment does, at least in the short-term postoperative course. A difference between these two techniques has not yet been substantiated. The rate of adjacent fractures occurring after cement augmentation is not higher than in conservatively treated patients.
Collapse
|
14
|
Stabilisierung der osteoporotischen Wirbelsäule unter biomechanischen Gesichtspunkten. DER ORTHOPADE 2010; 39:407-16. [DOI: 10.1007/s00132-009-1574-8] [Citation(s) in RCA: 6] [Impact Index Per Article: 0.4] [Reference Citation Analysis] [Track Full Text] [Subscribe] [Scholar Register] [Indexed: 10/19/2022]
|
15
|
Cortical bone trajectory for lumbar pedicle screws. Spine J 2009; 9:366-73. [PMID: 18790684 DOI: 10.1016/j.spinee.2008.07.008] [Citation(s) in RCA: 374] [Impact Index Per Article: 24.9] [Reference Citation Analysis] [Abstract] [Track Full Text] [Journal Information] [Submit a Manuscript] [Subscribe] [Scholar Register] [Received: 02/19/2008] [Revised: 06/02/2008] [Accepted: 07/20/2008] [Indexed: 02/03/2023]
Abstract
BACKGROUND CONTEXT Achieving solid implant fixation to osteoporotic bone presents a clinical challenge. New techniques and devices are being designed to increase screw-bone purchase of pedicle screws in the lumbar spine via a novel cortical bone trajectory that may improve holding screw strength and minimize loosening. Preliminary clinical evidence suggests that this new trajectory provides screw interference that is equivalent to the more traditionally directed trajectory for lumbar pedicle screws. However, a biomechanical study has not been performed to substantiate the early clinical results. PURPOSE Evaluate the mechanical competence of lumbar pedicle screws using a more medial-to-lateral path (ie, "cortical bone trajectory") than the traditionally used path. STUDY DESIGN Human cadaveric biomechanical study. METHODS Each vertebral level (L1-L5) was dual-energy X-ray absorptiometry (DXA) scanned and had two pedicle screws inserted. On one side, the traditional medially directed trajectory was drilled and tapped. On the contralateral side, the newly proposed cortical bone trajectory was drilled and tapped. After qCT scanning, screws were inserted into their respective trajectories and pullout and toggle testing ensued. In uniaxial pullout, the pedicle screw was withdrawn vertically from the constrained bone until failure occurred. The contralateral side was tested in the same manner. In screw toggle testing, the vertebral body was rigidly constrained and a longitudinal rod was attached to each screw head. The rod was grasped using a hydraulic grip and a quasi-static, upward displacement was implemented until construct failure. The contralateral pedicle screw was tested in the same manner. Yield pullout (N) and stiffness (N/mm) as well as failure moment (N-m) were compared and bone mineral content and bone density data were correlated with the yield pullout force. RESULTS New cortical trajectory screws demonstrated a 30% increase in uniaxial yield pullout load relative to the traditional pedicle screws (p=0.080), although mixed loading demonstrated equivalency between the two trajectories. No significant difference in construct stiffness was noted between the two screw trajectories in either biomechanical test or were differences in failure moments (p=0.354). Pedicle screw fixation did not appear to depend on bone quality (DXA) yet positive correlations were demonstrated between trajectory and bone density scans (qCT) and pullout force for both pedicle screws. CONCLUSIONS The current study demonstrated that the new cortical trajectory and screw design have equivalent pullout and toggle characteristics compared with the traditional trajectory pedicle screw, thus confirming preliminary clinical evidence. The 30% increase in failure load of the cortical trajectory screw in uniaxial pullout and its juxtaposition to higher quality bone justify its use in patients with poor trabecular bone quality.
Collapse
|