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

<sec><title>Study Design</title>Mechanical study.</sec><sec><title>Purpose</title>To compare the pullout strength of different screw designs and augmentation techniques in an osteoporotic bone model.</sec><sec><title>Overview of Literature</title>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.</sec><sec><title>Methods</title>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.</sec><sec><title>Results</title>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.</sec><sec><title>Conclusions</title>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.</sec>

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Novel Biodegradable Composite of Calcium Phosphate Cement and the Collagen I Mimetic P-15 for Pedicle Screw Augmentation in Osteoporotic Bone

Biomedicines ◽

10.3390/biomedicines9101392 ◽

2021 ◽

Vol 9 (10) ◽

pp. 1392

Author(s):

Harald Krenzlin ◽

Andrea Foelger ◽

Volker Mailänder ◽

Christopher Blase ◽

Marc Brockmann ◽

...

Keyword(s):

Calcium Phosphate ◽

Pedicle Screw ◽

Calcium Phosphate Cement ◽

Pedicle Screws ◽

Osteoblastic Differentiation ◽

Collagen I ◽

Osteoporotic Bone ◽

Mineral Density ◽

Screw Augmentation ◽

Pullout Loads

Osteoporotic vertebral fractures often necessitate fusion surgery, with high rates of implant failure. We present a novel bioactive composite of calcium phosphate cement (CPC) and the collagen I mimetic P-15 for pedicle screw augmentation in osteoporotic bone. Methods involved expression analysis of osteogenesis-related genes during osteoblastic differentiation by RT-PCR and immunostaining of osteopontin and Ca2+ deposits. Untreated and decalcified sheep vertebrae were utilized for linear pullout testing of pedicle screws. Bone mineral density (BMD) was measured using dual-energy X-ray absorptiometry (DEXA). Expression of ALPI II (p < 0.0001), osteopontin (p < 0.0001), RUNX2 (p < 0.0001), and osteocalcin (p < 0.0001) was upregulated after co-culture of MSC with CPC-P-15. BMD was decreased by 28.75% ± 2.6%. Pullout loads in untreated vertebrae were 1405 ± 6 N (p < 0.001) without augmentation, 2010 ± 168 N (p < 0.0001) after augmentation with CPC-P-15, and 2112 ± 98 N (p < 0.0001) with PMMA. In decalcified vertebrae, pullout loads were 828 ± 66 N (p < 0.0001) without augmentation, 1324 ± 712 N (p = 0.04) with PMMA, and 1252 ± 131 N (p < 0.0078) with CPC-P-15. CPC-P-15 induces osteoblastic differentiation of human MES and improves pullout resistance of pedicle screws in osteoporotic and non-osteoporotic bone.

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

BioMed Research International ◽

10.1155/2015/318405 ◽

2015 ◽

Vol 2015 ◽

pp. 1-11 ◽

Cited By ~ 2

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.

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Study on the application of internal fixation material implantation in the rehabilitation of spondylolisthesis in children

Materials Express ◽

10.1166/mex.2021.2011 ◽

2021 ◽

Vol 11 (8) ◽

pp. 1366-1372

Author(s):

Yongliang Liu ◽

Caijuan Chu ◽

Hua Gao ◽

Hong Jing

Keyword(s):

Bone Marrow ◽

High Pressure ◽

Calcium Phosphate ◽

Bone Cement ◽

Pedicle Screw ◽

Calcium Phosphate Cement ◽

Clinical Studies ◽

Pedicle Screws ◽

New Type ◽

Good Biocompatibility

Spondylolisthesis (SP), particularly lumbar SP in children, is mostly caused by dysplasia. Several clinical studies have revealed that bone cement filled with hollow pedicle screws can achieve great benefits in the treatment of SP. However, most of the existing bone cement materials are based on polymethyl methacrylate (PMMA) and calcium phosphate cement (CPC). However, PMMA has poor biocompatibility, due to which its actual efficacy is greatly reduced. Although CPC has good biocompatibility, it exhibits certain cytotoxicity and high pressure in the bone marrow, resulting in fat droplets in blood vessels, which may cause embolisms. This study aimed to investigate the actual efficacy of a new type of bone nanocement filled with hollow pedicle screw in the treatment of 11 children with lumbar SP and to provide a feasible surgical method for the treatment of lumbar SP with hollow pedicle screw filled with bone nanocement.

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Increased pedicle screw pullout strength with vertebroplasty augmentation in osteoporotic spines

Journal of Neurosurgery Spine ◽

10.3171/spi.2002.96.3.0309 ◽

2002 ◽

Vol 96 (3) ◽

pp. 309-312 ◽

Cited By ~ 30

Author(s):

John S. Sarzier ◽

Avery J. Evans ◽

David W. Cahill

Keyword(s):

Pedicle Screw ◽

Pedicle Screws ◽

Pullout Strength ◽

Mineral Density ◽

Content Type ◽

Pullout Force ◽

Grade Ii ◽

The Mean ◽

Grade Iii ◽

Fine Print

Object. The authors conducted a biomechanical study to evaluate pedicle screw pullout strength in osteoporotic cadaveric spines. Nonaugmented hemivertebrae were compared with pressurized polymethylmethacrylate (PMMA)—augmented hemivertebrae. Methods. Six formalin-fixed cadaveric thoracolumbar spines at least two standard deviations below the mean bone mineral density (BMD) for age were obtained. Radiographic and BMD studies were correlated to grades I, II, and III osteoporosis according to the Jekei scale. Each of the 21 vertebrae underwent fluoroscopic placement of 6-mm transpedicular screws with each hemivertebra serving as the control for the contralateral PMMA-augmented hemivertebra. Pedicle screws were then evaluated for biomechanical axial pullout resistance. Augmented hemivertebrae axial pullout forces were increased (p = 0.0005). The mean increase in pullout force was 181% for Grade I, 206% for Grade II, and 213% for Grade III osteoporotic spines. Augmented Grade I osteoporotic spines demonstrated axial pullout forces near those levels reported in the literature for nonosteoporotic specimens. Augmented Grade II osteoporotic specimens demonstrated increases to levels found in nonaugmented vertebrae with low-normal BMD. Augmented Grade III osteoporotic specimens had increases to levels equal to those found in nonaugmented Grade I vertebrae. Conclusions. Augmentation of osteoporotic vertebrae in PMMA-assisted vertebroplasty can significantly increase pedicle screw pullout forces to levels exceeding the strength of cortical bone. The maximum attainable force appears to be twice the pullout force of the nonaugmented pedicle screw for each osteoporotic grade.

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

Applied Sciences ◽

10.3390/app9081525 ◽

2019 ◽

Vol 9 (8) ◽

pp. 1525 ◽

Cited By ~ 1

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.

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The Effect on the Pullout Strength by the Timing of Pedicle Screw Insertion After Calcium Phosphate Cement Injection

Journal of Spinal Disorders & Techniques ◽

10.1097/bsd.0b013e3181dd7961 ◽

2011 ◽

Vol 24 (2) ◽

pp. 116-120 ◽

Cited By ~ 18

Author(s):

Woojin Cho ◽

Chunhui Wu ◽

Serkan Erkan ◽

Matthew M. Kang ◽

Amir A. Mehbod ◽

...

Keyword(s):

Calcium Phosphate ◽

Pedicle Screw ◽

Calcium Phosphate Cement ◽

Pullout Strength ◽

Screw Insertion ◽

Pedicle Screw Insertion ◽

Cement Injection

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

Applied Bionics and Biomechanics ◽

10.1155/2018/1460195 ◽

2018 ◽

Vol 2018 ◽

pp. 1-9 ◽

Cited By ~ 1

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.

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