Multiaxial Pedicle Screw Designs: Static and Dynamic Mechanical Testing

Stanford, Ralph; Loefler, Andreas Herman; Stanford, Philip Mark; Walsh, William R.

doi:10.1097/01.brs.0000092369.50397.85

Cited by 75 publications

(60 citation statements)

References 20 publications

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“…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. suggested that the rod–screw link design of the polyaxial screw reduces its static compressive bending yield strength as compared with the fixed screw designs.…”

Section: Discussionmentioning

confidence: 99%

“…In the past 20 years, the design and implantation techniques of the pedicle screw systems have been modified to reduce the rate of pedicle screw breakage and to facilitate easy application of the connecting rod without undue stress on the construct 13–16. The polyaxial head coupling of the pedicle screw was found to reduce the compression bending strength at the screw–rod mount, in comparison with a monoaxial screw design 1516…”

Section: Introductionmentioning

confidence: 99%

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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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Section: Discussionmentioning

confidence: 99%

Section: Introductionmentioning

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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“…To the best of our knowledge, no cases of spinal implant failure in such a unique situation have been reported in the literature. From a biomechanical perspective, it has been reported that the nut-locking mechanisms between the tulip-shaped head of the screw and the rod are vulnerable to fatigue stress [23]. The reason for the nut disassembly remains unclear but Kim [24] speculated that nut tightening with limited torque, nut cracking, and nut-thread failure, and wear between nut and rod could cause nut loosening.…”

Section: The Characteristics As For Cervical Instrumentation Failurementioning

confidence: 99%

Mechanical implant failure in posterior cervical spine fusion

et al. 2011

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Purpose The aim of this study was to determine whether the recent refinement and downsizing of the implants for posterior cervical fusion increase the occurrence of implant failure. Methods One hundred forty-two consecutive cases of cervical fusion, using either cannulated Magerl screws or a multiaxial pedicle screw-rod system, were reviewed retrospectively after an average follow-up period of more than 3 years, and the rate and characteristics of the failure of these implants were evaluated. Results Implant failure occurred in six (4.2%) patients: five with rheumatoid arthritis and one with athetoid cerebral palsy. Occipital plate fracture occurred in two patients, Magerl screw breakage in one patient, cervical pedicle screw fracture in two patients, and disassembly of the pedicle screw and rod in two patients (one with an occipital plate fracture). There was no rod fracture. The implant failures were asymptomatic, except in one patient. Disassembly of the pedicle screw and rod was observed immediately after another surgical procedure under general anesthesia in two patients. Conclusions The failure rate of 4.2% was similar to the rates reported in the literature for posterior lumbar spinal fusion, confirming the reliability of the recent cervical screw-rod system.

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“…This ability is fundamental for resistance against cyclic loading and a huge advantage of living tissue over dead materials. Pedicle screws, independently of design, sustain fatigue failure after five million cycles if loaded with 25% maximal load [30]. Normal walking frequency for Europeans is 1-3 million steps per year.…”

Section: Lessons From Osteoclastic Dysfunctionmentioning

confidence: 99%

Osteoclasts and Biomaterials

et al. 2006

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There is a growing market of biomaterials for orthopedic applications. As soon as these materials are surgically introduced into the constantly remodeling bone of the patient, they start to interact with the local cells: osteoblasts and osteoclasts. At the first glance, the bone building osteoblasts seem to be the more important cells for osseointegration of implants. However, it is mainly the bone resorbing action of osteclasts that determines the longevity of the implant. In this paper, we give a short overview over the current understanding of osteoclast biology; we review the interaction between biomaterials, biomaterial particles and osteoclasts, and the effects of treatment with antiosteoclastic agents like bisphosphonates on biomaterial implant healing.

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Multiaxial Pedicle Screw Designs: Static and Dynamic Mechanical Testing

Cited by 75 publications

References 20 publications

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

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

Mechanical implant failure in posterior cervical spine fusion

Osteoclasts and Biomaterials

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