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 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.

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.

scholarly journals Biomechanical evaluation of lumbar pedicle screws in spondylolytic vertebrae: comparison of fixation strength between the traditional trajectory and a cortical bone trajectory

2016 ◽  
Vol 24 (6) ◽  
pp. 910-915 ◽  
Author(s):  
Keitaro Matsukawa ◽  
Yoshiyuki Yato ◽  
Hideaki Imabayashi ◽  
Naobumi Hosogane ◽  
Takashi Asazuma ◽  
...  
Keyword(s):  
Cortical Bone ◽  
Pedicle Screws ◽  
Axial Rotation ◽  
Fixation Strength ◽  
Isthmic Spondylolisthesis ◽  
Pullout Strength ◽  
Lateral Bending ◽  
Cortical Bone Trajectory ◽  
Significant Difference ◽  
Flexion Extension

OBJECTIVE In the management of isthmic spondylolisthesis, the pedicle screw system is widely accepted surgical strategy; however, there are few reports on the biomechanical behavior of pedicle screws in spondylolytic vertebrae. The purpose of the present study was to compare fixation strength between pedicle screws inserted through the traditional trajectory (TT) and those inserted through a cortical bone trajectory (CBT) in spondylolytic vertebrae by computational simulation. METHODS Finite element models of spondylolytic and normal vertebrae were created from CT scans of 17 patients with adult isthmic spondylolisthesis (mean age 54.6 years, 10 men and 7 women). Each vertebral model was implanted with pedicle screws using TT and CBT techniques and compared between two groups. First, fixation strength of a single screw was evaluated by measuring axial pullout strength. Next, vertebral fixation strength of a paired-screw construct was examined by applying forces simulating flexion, extension, lateral bending, and axial rotation to vertebrae. RESULTS Fixation strengths of TT screws showed a nonsignificant difference between the spondylolytic and the normal vertebrae (p = 0.31–0.81). Fixation strength of CBT screws in the spondylolytic vertebrae demonstrated a statistically significant decrease in pullout strength (21.4%, p < 0.01), flexion (44.1%, p < 0.01), extension (40.9%, p < 0.01), lateral bending (38.3%, p < 0.01), and axial rotation (28.1%, p < 0.05) compared with those in the normal vertebrae. In the spondylolytic vertebrae, no statistically significant difference was observed for pullout strength between TT and CBT (p = 0.90); however, the CBT construct showed lower vertebral fixation strength in flexion (39.0%, p < 0.01), extension (35.6%, p < 0.01), lateral bending (50.7%, p < 0.01), and axial rotation (59.3%, p < 0.01) compared with the TT construct. CONCLUSIONS CBT screws are less optimal for stabilizing the spondylolytic vertebra due to their lower fixation strength compared with TT screws.

A biomechanical cadaveric analysis of polymethylmethacrylate-augmented pedicle screw fixation

2007 ◽  
Vol 7 (1) ◽  
pp. 47-53 ◽  
Author(s):  
Bruce M. Frankel ◽  
Sabino D'Agostino ◽  
Chiang Wang
Keyword(s):  
Pedicle Screw ◽  
Screw Fixation ◽  
Pedicle Screws ◽  
Pedicle Screw Fixation ◽  
Screw Placement ◽  
Pullout Strength ◽  
Mineral Density ◽  
Hardware Failure ◽  
Screw Augmentation ◽  
Valuable Adjunct

Object Instrumentation of the osteoporotic spine can be fraught with complications such as hardware failure. A cadaver study was performed to determine the biomechanical performance of polymethylmethacrylate (PMMA)–augmented pedicle screws. Methods Three osteoporotic human cadaveric specimens with a mean bone mineral density of 0.70 g/cm2 were used to evaluate the performance of a novel fenestrated bone tap in pedicle screw augmentation. On this device, tap threads serve a dual purpose in preventing backflow of cement toward neural elements while allowing for a custom form for subsequent screw placement. The tap was used to inject a mean volume of 3.7 ml PMMA/pedicle (range 2–8.0 ml PMMA/pedicle) followed by pedicle screw placement between L-5 and T-5, alternating between augmented and nonaugmented instrumentation. Axial pullout testing was then performed. Results Pedicle screw pullout strength was increased in both primary and salvage procedures by 119% (p = 0.001) and 162% (p = 0.01), respectively, after PMMA augmentation. Additionally, the injected cement volumes were divided into two groups, a low-cement group (≤ 2.8 ml/pedicle) and a high-cement group (≥ 5.5 ml/pedicle). Interestingly, the pullout strength did not significantly change with increased cement usage between the two groups (p > 0.05 for all comparisons). Conclusions Polymethylmethacrylate-augmented pedicle screw fixation results in a significant increase in the axial pullout strength of augmented pedicle screws in both primary and revision procedures. This technique may be a valuable adjunct in cases in which bolstering of the screw–bone interface is necessary.

Comparison of Pedicle Screw Loosening Mechanisms and the Effect on Fixation Strength

2015 ◽  
Vol 137 (12) ◽  
Author(s):  
Hedayeh Mehmanparast ◽  
Yvan Petit ◽  
Jean-Marc Mac-Thiong
Keyword(s):  
Pedicle Screw ◽  
Lumbar Vertebrae ◽  
Pedicle Screws ◽  
Pedicle Screw Fixation ◽  
Fixation Strength ◽  
Screw Loosening ◽  
Spinal Fixation ◽  
Bending Load ◽  
Biomechanical Evaluation ◽  
Pedicle Screw Loosening

Screw loosening is a common complication in spinal fixation using pedicle screws which may lead to loss of correction and revision surgery. The mechanisms of pedicle screw loosening are not well understood. The purpose of this study was to compare the pedicle screw pullout force and stiffness subsequent or not to multidirectional cyclic bending load (toggling). Pedicle screws inserted into porcine lumbar vertebrae underwent toggling in craniocaudal (CC), mediolateral (ML) directions, and no toggling (NT) before pullout. This study suggests that toggling and in particular CC toggling should be included in biomechanical evaluation of pedicle screw fixation strength.

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>

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