The Mechanical Effect of Rod Contouring on Rod-Screw System Strength in Spine Fixation

Acar, Nihat; Karakaşlı, Ahmet; Karaarslan, Ahmet; Özcanhan, Mehmet Hilal; Ertem, Fatih; Erduran, Mehmet

doi:10.3340/jkns.2016.59.5.425

Cited by 8 publications

(6 citation statements)

References 22 publications

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“…Moreover, it is concluded from biomechanical studies that work energy required for failure of kyphotic rod is lesser than that of a lordotic rod in a corpectomy model. [ 20 ] We feel that the unaddressed PJK because of delayed follow-up in the first and third case could have led to more stress at the VCR zone causing rod breakage at the site of VCR.…”

Section: Discussionmentioning

confidence: 99%

Proximal junctional kyphosis after pediatric angular kyphotic deformity correction: Are we missing something?

et al. 2021

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Purpose: Corrective maneuvers in an angular kyphotic deformity have its own problems including early complications such as neurological deficit and late complications such as proximal junctional kyphosis (PJK) and proximal junctional failure (PJF). This article discusses the probable mechanisms, leading to PJK in pediatric severe angular kyphotic deformities and preventive strategies for the same. We will also assess natural course of untreated PJK and its devastating consequences. Materials and Methods: Three patients, two 13-year males presented with progressive, painless thoracolumbar kyphoscoliotic deformity, with segmental kyphosis 100° and 140° and scoliosis of 33° and 78°, respectively, and one 14-year-old female presented with angular kyphotic deformity of 60° with apex at D11-12 level. Results: Posterior vertebral column resection with segmental deformity correction with good coronal and sagittal balance was done. In the follow-up, PJF was seen. Second surgery was done with the extension of instrumentation to D4 along with deformity correction in both the male patients. The female patient did not opt for a revision surgery, and we are following the natural history of this case. Conclusion: In severe thoracolumbar angular kyphotic deformities with normal or negative sagittal balance, it might be a safer option to select the sagittal stable vertebra as upper instrumented vertebra based on the C2 plumb line on the preoperative standing lateral radiographs. However, a study with a larger sample size is needed to validate our hypothesis.

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Section: Discussionmentioning

confidence: 99%

Proximal junctional kyphosis after pediatric angular kyphotic deformity correction: Are we missing something?

et al. 2021

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“…In this present experimental study, strain in rod at L4-L5 segment found as 250 microstrain for 8 Nm flexion and 340 microstrain for FE analysis. Acar et al (2016) performed mechanical testing on a corpectomy model under a compressive force of 100 N with 8.4 Nm moment in flexion-extension for different rod (titanium) curvatures (straight, kyphotic and lordotic) and found the mean values of strain for straight, kyphotic and lordotic rods as 1086 microstrain, 1244 microstrain and 1124 microstrain respectively under extension conditions [18].…”

Section: Discussionmentioning

confidence: 99%

Measurement of strain in the rod for lumbar pedicle screw fixation: An experimental and finite element study

Rana¹,

Biswas²,

Roy³

et al. 2020

Biomed. Phys. Eng. Express

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Spinal fusion with pedicle-screw-rod is being used widely for treating spinal deformities diseases. Several biomechanical studies on screw rod based implant failure through screw pullout, bending, screw breakage have been performed. But few studies are available regarding the effect of strain for breakage of rod. So, the purpose of the present study is to observe strain at the rod connected with the pedicle screw for different loading condition. The strain in stainless steel (SS) connecting rods for pedicle screw fixation were measured using strain gauge. In order to investigate the bio-mechanical response of lumbar spine with reference to strain in the rod, a simple experimental setup was developed using a specimen of L1-S spine segment. SS rods were used for pedicle screw implant on prototyped lumbar Spine. Prior to testing with pedicle screw, the lumbar spine specimen was also compared with FE results. The strain measured using strain gauges at L3-L4 level on SS rod were within a range of 85 to 310 microstrain under 6, 8, 10 Nm flexion and extension, and for L4-L5 level, these values were within a range of 95 to 440 microstrain. It was found that FE result was higher than the strain gauge result and the error varied between 10.5% to 33% with average error of 22.8%. However similar stain behavior was observed by the FE analysis. The proposed method, as well as the qualitative data, might be helpful for the researchers to understand biomechanical behavior of pedicle-screw implanted spine.

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“…4,5 In an experimental study performed with a corpectomy model to investigate the effects of straight, lordotic, and kyphotic rod contouring on the rod-screw fixation system, the lordotic system was found to be the most rigid one and the failure risk of rod-screw fixation was much higher than that of the kyphotic system. 6 Another experimental study demonstrated that rod contouring using a French bender affected the mechanical properties of the rods with the application of 0°, 10°, 20°, and 40° tangential rod bending angles. 7 That study concluded that rod contouring caused a reduction in yield strength and the stiffness of rods according to the degree of bending.…”

Section: Introductionmentioning

confidence: 99%

The effects of pre-stressed rods contoured by different bending techniques on posterior instrumentation of L4-L5 lumbar spine segment: A finite element study

Sengul

Özmen

Demir

2022

Proc Inst Mech Eng H

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Posterior pedicle screw instrumentation (PPSI) is a well-known method in lumbar spine surgery. Understanding how PPSI affects the biomechanics of the lumbar spine is an important issue. In particular, during PPSI operations, surgeons bend rods according to the patients’ spinal curvatures based on their own experiences. As a result, residual stresses develop on the rods due to this bending. Although many finite element-based biomechanical studies have been performed for PPSI, studies comparing the effects of residual stresses arising from rod contouring on the construct stresses are lacking. Thus, this study aimed to investigate the effects of residual stress in PPSI using rods contoured with a French bender and an in-situ bender, as well as comparing the differences in stress increment with straight and contoured rods for different physiological motions. Accordingly, a finite element (FE) model of the L4-L5 lumbar spine segment was developed for PPSI and the effects of residual stresses on rods were investigated by using different bending methods. In the simulations, it was found that rods contoured with a French bender with residual stress resulted in significantly more increased stress in PPSI compared to those contoured with an in-situ bender. The results of this study emphasize that increased stress in PPSI due to the residual stresses for different physiological motions may increase the risk of PPSI failures. Additionally, the finite element modeling approach employed here could be used as a fundamental tool for further investigations of topics such as PPSI fatigue life and failure studies.

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The Mechanical Effect of Rod Contouring on Rod-Screw System Strength in Spine Fixation

Cited by 8 publications

References 22 publications

Proximal junctional kyphosis after pediatric angular kyphotic deformity correction: Are we missing something?

Proximal junctional kyphosis after pediatric angular kyphotic deformity correction: Are we missing something?

Measurement of strain in the rod for lumbar pedicle screw fixation: An experimental and finite element study

The effects of pre-stressed rods contoured by different bending techniques on posterior instrumentation of L4-L5 lumbar spine segment: A finite element study

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