Physical Characteristics of Polyaxial-Headed Pedicle Screws and Biomechanical Comparison of Load With Their Failure

Fogel, Guy R.; Reitman, Charles A.; Liu, Weiqiang; Esses, Stephen I.

doi:10.1097/01.brs.0000048652.45964.2e

Cited by 63 publications

(38 citation statements)

References 13 publications

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“…Thunder expandable screw system is another multiaxial expandable instrument. Another significant advantage of the multiaxial design is preventing pedicle screw breakage [22]. This is more important in the hollow-structured pedicle screws whose fatigue strength is lower than that of the solidstructured screws.…”

Section: Discussionmentioning

confidence: 99%

A comparative study on screw loosening in osteoporotic lumbar spine fusion between expandable and conventional pedicle screws

Gong

Liu

et al. 2011

Arch Orthop Trauma Surg

156

110

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Section: Discussionmentioning

confidence: 99%

A comparative study on screw loosening in osteoporotic lumbar spine fusion between expandable and conventional pedicle screws

Gong

Liu

et al. 2011

Arch Orthop Trauma Surg

156

110

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“…However, polyaxial head coupling to the screw is a weak link that may cause less strength at the screw-head interface. 33 Lehman et al 14 compared the straightforward versus the anatomic trajectory pedicle screw on cadaveric thoracic vertebra using MIT, POS, and BMD to determine the optimal biomechanical sagittal trajectory for placement of a thoracic pedicle screw. The straightforward technique resulted in a 39% increase in MIT and a 27% increase in POS compared with the anatomic trajectory technique.…”

Section: Discussionmentioning

confidence: 99%

Biomechanical Comparison of Anatomic Trajectory Pedicle Screw versus Injectable Calcium Sulfate Graft-Augmented Pedicle Screw for Salvage in Cadaveric Thoracic Bone

Derinçek

Mehbod

et al. 2006

Journal of Spinal Disorders &Amp; Techniques

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Many salvage options for failed thoracic pedicle screws exist including the use of a different trajectory or the augmentation of the screw with polymethylmethacrylate cement. Although polymethylmethacrylate immediately increases the construct stiffness and the pull-out strength, it may cause bone necrosis, toxin relaxation, and/or neural injury. On the other hand, calcium sulfate bone grafts have a high potential for biologic incorporation and no thermal damage effect. In the current study, polyaxial pedicle screws were first inserted with a straightforward approach on both sides in 17 fresh human cadaveric thoracic vertebrae. The maximal insertion torque for each screw was measured and then the pull-out strengths were recorded. Afterward, these pedicle screws were randomly assigned to be replaced either by graft augmentation or by anatomic trajectory technique for salvage. The graft-augmented screws were placed using the previous holes. The maximum insertional torque for each anatomic trajectory screw was measured. Finally, the pull-out strengths of the revision screws were recorded. The mean maximum insertional torque decreased with the anatomic trajectory salvage technique when compared with the straightforward approach, 0.23 versus 0.38 Nm, respectively (P=0.003). The anatomic trajectory revision resulted in decreased pull-out strength when compared with the pull-out strength of the straightforward technique, 297 versus 469 N, respectively (P=0.003). The calcium sulfate graft augmentation increased the pull-out strength when compared with the pull-out strength of the straightforward technique, 680 versus 477 N, respectively (P=0.017). The mean pull-out strength ratio of revised screw to original was 0.71 for anatomic trajectory and 1.8 for graft-augmented screws, a statistically significant difference (P=0.002).

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“…When using monoaxial screws, the addition of an intermediate forces the surgeon to bend the connecting rod to accommodate the additional screw. Polyaxial screws, on the other hand, facilitate the installation of the connecting rod, and their biomechanical properties have been reported in several studies 14–1623. Stanford et al 15.…”

Section: Discussionmentioning

confidence: 99%

Biomechanical efficacy of monoaxial or polyaxial pedicle screw and additional screw insertion at the level of fracture, in lumbar burst fracture: An experimental study

Wang

Liu

et al. 2012

IJOO

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Background:Use of a pedicle screw at the level of fracture, also known as an intermediate screw, has been shown to improve clinical results in managing lumbar fracture, but there is a paucity of biomechanical studies to support the claim. The aim of this study was to evaluate the effect of adding intermediate pedicle screws at the level of a fracture on the stiffness of a short-segment pedicle fixation using monoaxial or polyaxial screws and to compare the strength of monoaxial and polyaxial screws in the calf spine fracture model.Materials and Methods:Flexibility of 12 fresh-frozen calf lumbar spine specimens was evaluated in all planes. An unstable burst fracture model was created at the level of L3 by the pre-injury and dropped-mass technique. The specimens were randomly divided into monoaxial pedicle screw (MPS) and polyaxial pedicle screw (PPS) groups. Flexibility was retested without and with intermediate screws (MPSi and PPSi) placed at the level of fracture in addition to standard screws placed at L2 and L4.Results:The addition of intermediate screws significantly increased the stability of the constructs, as measured by a decreased range of motion (ROM) in flexion, extension, and lateral bending in both MPS and PPS groups (P < 0.05). There was neither any significant difference in the ROM in the spines of the two groups before injury, nor a difference in the ROM between the MPSi and PPSi groups (P > 0.05), but there was a significant difference between MPS and PPS in flexion and extension in the short-segment fixation group (P < 0.05).Conclusions:The addition of intermediate screws at the level of a burst fracture significantly increased the stability of short-segment pedicle screw fixation in both the MPS and PPS groups. However, in short-segment fixation group, monoaxial pedicle screw exhibited more stability in flexion and extension than the polyaxial pedicle screw.

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Physical Characteristics of Polyaxial-Headed Pedicle Screws and Biomechanical Comparison of Load With Their Failure

Cited by 63 publications

References 13 publications

A comparative study on screw loosening in osteoporotic lumbar spine fusion between expandable and conventional pedicle screws

A comparative study on screw loosening in osteoporotic lumbar spine fusion between expandable and conventional pedicle screws

Biomechanical Comparison of Anatomic Trajectory Pedicle Screw versus Injectable Calcium Sulfate Graft-Augmented Pedicle Screw for Salvage in Cadaveric Thoracic Bone

Biomechanical efficacy of monoaxial or polyaxial pedicle screw and additional screw insertion at the level of fracture, in lumbar burst fracture: An experimental study

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