Relationship of forces acting on implant rods and degree of scoliosis correction

Salmingo, Remel A.; Tadano, Shigeru; Fujisaki, Kazuhiro; Abe, Yuichiro; Ito, Manabu

doi:10.1016/j.clinbiomech.2012.12.001

Cited by 28 publications

(34 citation statements)

References 18 publications

(14 reference statements)

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“…High implant density has not shown improvement in patient reported outcomes [38][39][40][41][42][43][44] or cosmesis [39], and has contributed to less thoracic kyphosis [38,40,41], and high costs [42,45]. In contrast to what might be expected, it was shown through a finite element analysis and computational study that high implant density does not improve the distribution of forces and correction [46,47].…”

Section: Supporting Empirical Evidencementioning

confidence: 95%

Optimal surgical care for adolescent idiopathic scoliosis: an international consensus

et al. 2014

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Purpose The surgical management of adolescent idiopathic scoliosis (AIS) has seen many developments in the last two decades. Little high-level evidence is available to support these changes and guide treatment. This study aimed to identify optimal operative care for adolescents with AIS curves between 40°and 90°Cobb angle. Methods From July 2012 to April 2013, the AOSpine Knowledge Forum Deformity performed a modified Delphi survey where current expert opinion from 48 experienced deformity surgeons, representing 29 diverse countries, was gathered. Four rounds were performed: three web-based surveys and a final face-to-face meeting. Consensus was achieved with C70 % agreement. Data were analyzed qualitatively and quantitatively.Results Consensus of what constitutes optimal care was reached on greater than 60 aspects including: preoperative radiographs; posterior as opposed to anterior (endoscopic) surgical approaches; use of intraoperative spinal cord monitoring; use of local autologous bone (not iliac crest) for grafts; use of thoracic and lumbar pedicle screws; use of titanium anchor points; implant density of \80 % for 40°-70°curves; and aspects of postoperative care. Variability in practice patterns was found where there was no consensus. In addition, there was consensus on what does not constitute optimal care, including: routine pre-and intraoperative traction; routine anterior release; use of bone morphogenetic proteins; and routine postoperative CT scanning. operative care for adolescents with AIS. In the absence of current high-level evidence, at present, these expert opinion findings will aid health care providers worldwide define appropriate care in their regions. Areas with no consensus provide excellent insight and priorities for future research.

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Section: Supporting Empirical Evidencementioning

confidence: 95%

Optimal surgical care for adolescent idiopathic scoliosis: an international consensus

et al. 2014

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“…3D-CAD model of rod geometry was generated and Finite Element Analysis (FEA) was performed using ANSYS 11.0 according to the previously developed method reported by Salmingo et al [ 12 , 13 ]. Material properties of this rod are Young's Modulus (E), yield stress (σY), yield strain (εY) and hardening coefficient (H) equal to105 GPa, 900 MPa, 8.57×10−3 and 2.41 GPa, respectively.…”

Section: Femmentioning

confidence: 99%

“…The rod geometry was used to define the direction of the pullout or push-in force because its curvature constitutes the spine curvature after the surgical treatment of scoliosis. The rod geometry was approximated by quintic polynomial function using the previous method [ 13 ]. A tangent angle β that is orthogonal to the pullout or push-in force axis was computed by evaluating the derivative of quintic polynomial function evaluated for location of each screw.…”

Section: Femmentioning

confidence: 99%

“…However, there were only few reports which estimated the actual corrective force during correction maneuver in vivo [ 10 , 11 ]. We have developed a novel method for estimating corrective force acting on the spine by investigating the geometrical change of implanted rod in scoliosis surgery [ 12 , 13 ]. In the present study, estimated corrective forces and pull out forces exerted on the pedicle screw were analyzed using a novel method based on finite element analysis.…”

Section: Introductionmentioning

confidence: 99%

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Scoliosis corrective force estimation from the implanted rod deformation using 3D-FEM analysis

Abe

Ito

Abumi³

et al. 2015

Scoliosis

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BackgroundImprovement of material property in spinal instrumentation has brought better deformity correction in scoliosis surgery in recent years. The increase of mechanical strength in instruments directly means the increase of force, which acts on bone-implant interface during scoliosis surgery. However, the actual correction force during the correction maneuver and safety margin of pull out force on each screw were not well known. In the present study, estimated corrective forces and pull out forces were analyzed using a novel method based on Finite Element Analysis (FEA).MethodsTwenty adolescent idiopathic scoliosis patients (1 boy and 19 girls) who underwent reconstructive scoliosis surgery between June 2009 and Jun 2011 were included in this study. Scoliosis correction was performed with 6mm diameter titanium rod (Ti6Al7Nb) using the simultaneous double rod rotation technique (SDRRT) in all cases. The pre-maneuver and post-maneuver rod geometry was collected from intraoperative tracing and postoperative 3D-CT images, and 3D-FEA was performed with ANSYS. Cobb angle of major curve, correction rate and thoracic kyphosis were measured on X-ray images.ResultsAverage age at surgery was 14.8, and average fusion length was 8.9 segments. Major curve was corrected from 63.1 to 18.1 degrees in average and correction rate was 71.4%. Rod geometry showed significant change on the concave side. Curvature of the rod on concave and convex sides decreased from 33.6 to 17.8 degrees, and from 25.9 to 23.8 degrees, respectively. Estimated pull out forces at apical vertebrae were 160.0N in the concave side screw and 35.6N in the convex side screw. Estimated push in force at LIV and UIV were 305.1N in the concave side screw and 86.4N in the convex side screw.ConclusionsCorrective force during scoliosis surgery was demonstrated to be about four times greater in the concave side than in convex side. Averaged pull out and push in force fell below previously reported safety margin. Therefore, the SDRRT maneuver was safe for correcting moderate magnitude curves. To prevent implant breakage or pedicle fracture during the maneuver in a severe curve correction, mobilization of spinal segment by releasing soft tissue or facet joint could be more important than using a stronger correction maneuver with a rigid implant.

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“…In addition, biomechanical comparison of alternative screw densities for AIS has indicated that increased numbers of pedicle screws did not provide a higher degree of correction. 26,32 Furthermore, an international consensus suggested that an implant density less than 80% was optimal (73% vs 27%) for moderate curves with a Cobb angle of 40°-70°. 5 As to sagittal correction, pooled data on thoracic kyphosis were available in 8 studies, involving a total of 475 patients, and no significant differences were found (p = 0.26, I 2 = 79%).…”

Section: Discussionmentioning

confidence: 99%

Does higher screw density improve radiographic and clinical outcomes in adolescent idiopathic scoliosis? A systematic review and pooled analysis

Luo

Wang

Shen

et al. 2017

PED

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OBJECTIVE The radiographic and clinical outcomes of low-density (LD) versus high-density (HD) screw constructs in patients with adolescent idiopathic scoliosis (AIS) treated with all–pedicle screw constructs are still controversial. A systematic review and pooled analysis were performed to compare radiographic, perioperative, and quality-of-life (QOL) outcomes and complications in patients with moderate AIS treated with LD or HD screw constructs. METHODS The MEDLINE, Embase, and Web of Science databases were searched for English-language articles addressing LD versus HD screw constructs in AIS patients treated with all–pedicle screw constructs. The division of LD and HD groups was based on relative screw density and screw techniques. This systematic analysis strictly followed the PRISMA (Preferred Reporting Items for Systematic Reviews and Meta-Analyses) guidelines, and all articles included in the analysis met the criteria specified in the guidelines. Two reviewers independently assessed the quality of the studies using the Newcastle-Ottawa Scale. Date on radiographic, perioperative, and QOL outcomes and complications were extracted from the included studies. RESULTS Twelve studies, involving a total of 827 patients (480 treated with LD constructs, 347 with HD), were analyzed—1 randomized controlled trial, 1 quasi-randomized controlled trial, and 10 retrospective studies. The patients' age at surgery, preoperative Cobb angle of the major curve, amount of thoracic kyphosis, and major curve flexibility were reasonably distributed, and no statistically significant differences were found. Regarding the outcomes at most recent follow-up, there were no significant differences in the Cobb angle of the major curve (mean difference 0.96°, 95% CI −0.06° to 1.98°, p = 0.06, I2 = 1%), major curve correction (mean difference −0.72%, 95% CI −2.96% to 1.52%, p = 0.53, I2 = 0%), thoracic kyphosis (mean difference −1.67°, 95% CI −4.59° to 1.25°, p = 0.26, I2 = 79%), complications (odds ratio [OR] 0.66, 95% CI 0.31–1.42, p = 0.29, I2 = 0%), and QOL outcomes. Reduced operative time (mean difference −48.56 minutes, 95% CI −82.69 to −14.43 minutes, p = 0.005, I2 = 87%), blood loss (mean difference −77.85 ml, 95% CI −153.10 to −2.60 ml, p = 0.04, I2 = 0%), and hospital charges (mean difference −$5.92K, 95% CI −$6.59K to −$5.26K, p < 0.00001, I2 = 0%) were found in the LD group, compared with the HD group. CONCLUSIONS LD and HD screw constructs are both associated with satisfactory radiographic and QOL outcomes with few complications. This study supports the use of LD screw constructs for the treatment of moderate AIS, because they resulted in reduced operative time, blood loss, and hospital charges while maintaining radiographic and QOL outcomes and complication rates similar to those achieved with HD screw constructs.

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Relationship of forces acting on implant rods and degree of scoliosis correction

Cited by 28 publications

References 18 publications

Optimal surgical care for adolescent idiopathic scoliosis: an international consensus

Optimal surgical care for adolescent idiopathic scoliosis: an international consensus

Scoliosis corrective force estimation from the implanted rod deformation using 3D-FEM analysis

Does higher screw density improve radiographic and clinical outcomes in adolescent idiopathic scoliosis? A systematic review and pooled analysis

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