scholarly journals Comparison of the Pullout Strength of Pedicle Screws According to the Thread Design for Various Degrees of Bone Quality

2019 ◽  
Vol 9 (8) ◽  
pp. 1525 ◽  
Author(s):  
Shen ◽  
Kim ◽  
Kang ◽  
Yeom
Keyword(s):  
Cortical Bone ◽  
Pedicle Screw ◽  
Bone Quality ◽  
Cancellous Bone ◽  
Pedicle Screws ◽  
Type A ◽  
Osteoporotic Bone ◽  
Type I ◽  
Pullout Strength ◽  
Type C

Although dual-threaded pedicle screws have been developed, the advantages over single-threaded screws remain controversial. We aimed to investigate the biomechanical performance of two types of dual-threaded pedicle screw by comparing their pullout strength with that of a single-threaded screw in relation to bone quality. Four types of pedicle screw with different thread patterns were designed. Type I: single-threaded screw; Type II: double-threaded screw; Type III: dual-threaded screw; Type IV: a newly designed double dual-threaded screw. Five types of polyurethane foams simulating various degrees of bone quality were used. These were: Type A: cancellous bone; Type B: cancellous bone with cortical bone in the upper margin; Type C: osteoporotic cancellous bone; Type D: osteoporotic cancellous bone with cortical bone in the upper margin; and Type E: osteoporotic bone with cortical bone in the upper and lower margins. A comparison of the pullout strength of Type I, II, and III screws in Type A, B, C and D bone specimens was performed. Type C and E bone specimens were used for comparisons among Type I, II, and IV screws. Compared to the single-threaded screw, the dual-threaded pedicle screws exhibited higher pullout strength in normal-quality bone and significantly lower pullout strength in compromised osteoporotic bone. However, the double dual-threaded screw exhibited better pullout biomechanics in osteoporotic bone with bi-cortical bone.

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

2015 ◽  
Vol 2015 ◽  
pp. 1-11 ◽  
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.

scholarly journals Pedicle screw placement in the lumbar spine: effect of trajectory and screw design on acute biomechanical purchase

2015 ◽  
Vol 22 (5) ◽  
pp. 503-510 ◽  
Author(s):  
Steven Wray ◽  
Ronnie Mimran ◽  
Sasidhar Vadapalli ◽  
Snehal S. Shetye ◽  
Kirk C. McGilvray ◽  
...  
Keyword(s):  
Bone Mineral Density ◽  
Lumbar Spine ◽  
Cortical Bone ◽  
Pedicle Screw ◽  
Bone Quality ◽  
Pedicle Screws ◽  
Biomechanical Study ◽  
Mineral Density ◽  
High Quality ◽  
Cortical Screw

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.

scholarly journals Effects of the Insertion Type and Depth on the Pedicle Screw Pullout Strength: A Finite Element Study

2018 ◽  
Vol 2018 ◽  
pp. 1-9 ◽  
Author(s):  
K. Jendoubi ◽  
Y. Khadri ◽  
M. Bendjaballah ◽  
N. Slimane
Keyword(s):  
Finite Element ◽  
Pedicle Screw ◽  
Pedicle Screws ◽  
Osteoporotic Bone ◽  
Screw Thread ◽  
Pullout Strength ◽  
Pullout Resistance ◽  
Finite Element Study ◽  
Screw Breakage ◽  
Element Study

Purpose. The pedicle screw is a surgical device that has become widely used in spinal fixation and stabilization. Postsurgical complications such as screw loosening due to fatigue loading and screw breakage still need investigations. Clinical parameters such as the screw insertion type and depth, the bone density, and the patient degree of mobility greatly affect the mechanisms of the implant’s failure/success. Methods. The current finite element study focused on the prediction of the pedicle screw pullout strength under various conditions such as insertion type, insertion depth, bone quality, and loading mode. Results. As depicted in this study, the preservation of the pedicle cortex as in the N1 insertion technique greatly enhances the pullout resistance. In addition, the higher the screw-anchoring depth, permitting to gear a maximum number of threads, the better the protection against premature breakouts of pedicle screws. Conclusions. In agreement with experimental data, the type of insertion in which the first screw thread is placed immediately after the preserved pedicle cortex showed the best pullout resistance for both normal and osteoporotic bone.

scholarly journals Comparison of the Pullout Strength of Different Pedicle Screw Designs and Augmentation Techniques in an Osteoporotic Bone Model

2018 ◽  
Vol 12 (1) ◽  
pp. 3-11 ◽  
Author(s):  
Gorkem Kiyak ◽  
Tevfik Balikci ◽  
Ahmed Majid Heydar ◽  
Murat Bezer
Keyword(s):  
Calcium Phosphate ◽  
Pedicle Screw ◽  
Calcium Phosphate Cement ◽  
Pedicle Screws ◽  
Osteoporotic Bone ◽  
Cannulated Screws ◽  
Pullout Strength ◽  
Pullout Force ◽  
Bone Screw ◽  
Augmentation Techniques

<sec><title>Study Design</title><p>Mechanical study.</p></sec><sec><title>Purpose</title><p>To compare the pullout strength of different screw designs and augmentation techniques in an osteoporotic bone model.</p></sec><sec><title>Overview of Literature</title><p>Adequate bone screw pullout strength is a common problem among osteoporotic patients. Various screw designs and augmentation techniques have been developed to improve the biomechanical characteristics of the bone–screw interface.</p></sec><sec><title>Methods</title><p>Polyurethane blocks were used to mimic human osteoporotic cancellous bone, and six different screw designs were tested. Five standard and expandable screws without augmentation, eight expandable screws with polymethylmethacrylate (PMMA) or calcium phosphate augmentation, and distal cannulated screws with PMMA and calcium phosphate augmentation were tested. Mechanical tests were performed on 10 unused new screws of each group. Screws with or without augmentation were inserted in a block that was held in a fixture frame, and a longitudinal extraction force was applied to the screw head at a loading rate of 5 mm/min. Maximum load was recorded in a load displacement curve.</p></sec><sec><title>Results</title><p>The peak pullout force of all tested screws with or without augmentation was significantly greater than that of the standard pedicle screw. The greatest pullout force was observed with 40-mm expandable pedicle screws with four fins and PMMA augmentation. Augmented distal cannulated screws did not have a greater peak pullout force than nonaugmented expandable screws. PMMA augmentation provided a greater peak pullout force than calcium phosphate augmentation.</p></sec><sec><title>Conclusions</title><p>Expandable pedicle screws had greater peak pullout forces than standard pedicle screws and had the advantage of augmentation with either PMMA or calcium phosphate cement. Although calcium phosphate cement is biodegradable, osteoconductive, and nonexothermic, PMMA provided a significantly greater peak pullout force. PMMA-augmented expandable 40-mm four-fin pedicle screws had the greatest peak pullout force.</p></sec>

Pullout strength for cannulated pedicle screws with bone cement augmentation in severely osteoporotic bone: Influences of radial hole and pilot hole tapping

2009 ◽  
Vol 24 (8) ◽  
pp. 613-618 ◽  
Author(s):  
Lih-Huei Chen ◽  
Ching-Lung Tai ◽  
Po-Liang Lai ◽  
De-Mei Lee ◽  
Tsung-Tin Tsai ◽  
...  
Keyword(s):  
Bone Cement ◽  
Pedicle Screws ◽  
Cement Augmentation ◽  
Osteoporotic Bone ◽  
Pullout Strength ◽  
Pilot Hole

scholarly journals Placement of Guide-Wireless Sharp Percutaneous Pedicle Screws Utilizing Computed Tomography-Navigation and Sentinel Fluoroscopy: 2-Dimensional Operative Video

2019 ◽  
Vol 19 (2) ◽  
pp. E149-E150 ◽  
Author(s):  
Nikolay L Martirosyan ◽  
Joshua T Wewel ◽  
Juan S Uribe
Keyword(s):  
Computed Tomography ◽  
Pedicle Screw ◽  
Pedicle Screws ◽  
Transverse Process ◽  
Screw Placement ◽  
Osteoporotic Bone ◽  
Screw Insertion ◽  
Institutional Review ◽  
Stab Incision ◽  
Anterior Posterior

Abstract Many established techniques exist for minimally invasive pedicle screw placement. Nearly all techniques incorporate the use of a Kershner wire (K-wire) at various points in the work-flow. The use of a K-wire adds an additional step. If its position is lost, it requires repeating all previous steps, and placement is not without complication. The use of a guide-wireless sharp screws allows the surgeon to place a pedicle screw in 1 step with several fluid maneuvers.1 The patient underwent Institutional Review Board-approved consent for this study. Following traditional computed tomography-based navigation, a stab incision is made, followed by fascial dissection with monopolar cautery. The sharp screw is placed percutaneously at the facet-transverse process junction. The precise entry point is confirmed with navigation, followed by a sentinel anterior-posterior fluoroscopic image, verifying the accuracy of the navigation. The cortical bone is traversed by malleting the sharp tip through the cortex. When the cancellous bone is engaged, the screw is then advanced through the pedicle. This set of steps allows for safe, efficient placement of percutaneous pedicle screws without the need for a guidewire. Mal-placement regarding sharp pedicle screw insertion is similar to K-wire-dependent screw placement. Surgeons must be cognoscente of exceptionally sclerotic bone, which can prove difficult to cannulate. Conversely, osteoporotic bone that is liable to a cortical pedicle breach, transverse process fracture, and/or maltrajectory are all considerations when placing a K-wireless, sharp pedicle screw. Anterior-posterior fluoroscopy is utilized to confirm accuracy of image-guided navigation and mitigate malplacement of pedicle screws.

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

2018 ◽  
Vol 21 (2) ◽  
pp. 190-196 ◽  
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.

Biomechanical Effects of Lumbar Pedicle Screw Insertion Depth on Screw Loosening and Fulcrum Location

2013 ◽  
Author(s):  
Laura E. Buckenmeyer ◽  
Kristophe J. Karami ◽  
Ata M. Kiapour ◽  
Vijay K. Goel ◽  
Constantine K. Demetropoulos ◽  
...  
Keyword(s):  
Pedicle Screw ◽  
Pedicle Screws ◽  
Screw Loosening ◽  
Pullout Strength ◽  
Insertion Depth ◽  
Bone Implant ◽  
Screw Insertion ◽  
Pedicle Screw Insertion ◽  
Increased Risk ◽  
Screw Length

Osteoporosis is a critical challenge in orthopedic surgery. Osteoporotic patients have an increased risk of loosening and failure of implant constructs due to a weaker bone-implant interface than with healthy bone. Pullout strength of pedicle screws is enhanced by increased screw insertion depth. However, more knowledge is needed to define optimal pedicle screw insertion depth in relation to screw-bone interface biomechanics and the resulting loosening risk. This study evaluates the effects of screw length on loosening risk in the osteoporotic lumbar spine.

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