Biomechanical study on three screw-based atlantoaxial fixation techniques: A finite element study

Study Design: This is a finite element study. Purpose: This study is aimed to compare the biomechanical behaviors of three screw-based atlantoaxial fixation techniques. Overview of Literature: Screw-based constructs that are widely used to stabilize the atlantoaxial joint come with their own challenges in surgery. Clinical and in vitro studies have compared the effectiveness of screw-based constructs in joint fixation. Nevertheless, there is limited information regarding the biomechanical behavior of these constructs, such as the stresses and strains they experience. Methods: A finite element model of the upper cervical spine was developed. A type II dens fracture was induced in the intact model to produce the injured model. The following three constructs were simulated on the intact and injured models: transarticular screw (C1– C2TA), lateral mass screw in C1 and pedicle screw in C2 (C1LM1–C2PD), and lateral mass screw in C1 and translaminar screw in C2 (C1LM1–C2TL). Results: In the intact model, flexion–extension range of motion (ROM) was reduced by up to 99% with C11–C2TA and 98% with C1LM1–C2PD and C1LM1–C2TL. The lateral bending ROM in the intact model was reduced by 100%, 95%, and 75% with C11–C2TA, C1LM1–C2PD, and C1LM1–C2TL, respectively. The axial rotation ROM in the intact model was reduced by 99%, 98%, and 99% with C11–C2TA, C1LM1–C2PD, and C1LM1–C2TL, respectively. The largest maximum von Mises stress was predicted for C1LM1–C2TL (332 MPa) followed by C1LM1–C2PD (307 MPa) and C11–C2TA (133 MPa). Maximum stress was predicted to be at the lateral mass screw head of the C1LM1–C2TL construct. Conclusions: Our model indicates that the biomechanical stability of the atlantoaxial joint in lateral bending with translaminar screws is not as reliable as that with transarticular and pedicle screws. Translaminar screws experience large stresses that may lead to failure of the construct before the required bony fusion occurs

A new lumbar fixation device alternative to pedicle-based stabilization for lumbar spine: In vitro cadaver investigation

Context: To evaluate the stability provided by a new bilateral fixation technique using an in vitro investigation for posterior lumbar segmental instrumentation. Design: Experimental cadaver study. In this study, we propose an alternative technique for a posterior lumbar fixation technique called “inferior-oblique transdiscal fixation” (IOTF). Setting: Study performed at Engineering Center for Orthopedic Research Exellence (ECORE) in Toledo University-Ohio. Participants: Six human lumbar cadaveric specimen used in this study. Interventions: In this study, we propose an alternative technique for a posterior lumbar fixation technique called “inferior-oblique transdiscal fixation” (IOTF). As a novel contribution to the classical technique, the entry point of the screw is the supero-lateral point of the intersecting line drawn between the corpus and the pedicle of the upper vertebra. This approach enables the fixation of two adjacent vertebrae using a single screw on each side without utilizing connecting rods. Outcome Measures: Flexion (Flex), extension (Ext), right and left lateral bending (LB & RB), and right and left axial rotation (LR & RR), and the position data were captured at each load step using the Optotrak motion measurement system and compared for IOTF and posterior transpedicular stabilization. Results: The Posterior stabilization system (PSS) and IOTF significantly reduced the ROM of L4-L5 segment compared to intact segment’s ROM. During axial rotation (AR) IOTF fused index segment more than PSS. Besides this, addition of transforaminal lumbar interbody fusion (TLIF) cage improved the stabilization of IOTF system during flexion, extension and lateral bending. Whereas, PSS yielded better fusion results during extension compared to IOTF with and without interbody fusion cages. Conclusions: We hypothesized that the new posterior bilateral system would significantly decrease motion compared to the intact spine. This cadaver study showed that the proposed new posterior fusion technique IOTF fused the index segment in a similar fashion to the classical pedicle screw fusion technique.National Science Foundation (NSF)University of Toledo, Toledo, O

Investigation into cervical spine biomechanics following single, multilevel and hybrid disc replacement surgery with dynamic cervical implant and fusion: A finite element study

Cervical fusion has been a standard procedure for treating abnormalities associated with the cervical spine. However, the reliability of anterior cervical discectomy and fusion (ACDF) has become arguable due to its adverse effects on the biomechanics of adjacent segments. One of the drawbacks associated with ACDF is adjacent segment degeneration (ASD), which has served as the base for the development of dynamic stabilization systems (DSS) and total disc replacement (TDR) devices for cervical spine. However, the hybrid surgical technique has also gained popularity recently, but its effect on the biomechanics of cervical spine is not well researched. Thus, the objective of this FE study was to draw a comparison among single-level, bi-level, and hybrid surgery with dynamic cervical implants (DCIs) with traditional fusion. Reductions in the range of motion (ROM) for all the implanted models were observed for all the motions except extension, compared to for the intact model. The maximum increase in the ROM of 42% was observed at segments C5–C6 in the hybrid DCI model. The maximum increase in the adjacent segment’s ROM of 8.7% was observed in the multilevel fusion model. The maximum von Mises stress in the implant was highest for the multilevel DCI model. Our study also showed that the shape of the DCI permitted flexion/extension relatively more compared to lateral bending and axial rotation

Influence of three-dimensional reconstruction method for building a model of the cervical spine on its biomechanical responses: A finite element analysis study

In some finite element analysis studies of models of sections of the spine, the three-dimensional solid model is built by assuming symmetry about the mid-sagittal plane of the section, whereas in other studies, the model is built from the exact geometry of the section. The influence of the method used to build the solid model on model parameters, in the case of the cervical spine, has not been reported in the literature. This issue is the subject of this study, with the section being C2-C7, the applied loadings being extension, flexion, left lateral bending, and right axial rotation (each of magnitude 1 Nm), and the model parameters determined being rotation, intradiskal pressure, and facet load at each of the segments. When all the parameter results were considered, it was found that, by and large, the influence of solid model construction method used (exact geometry vs assumption of symmetry about the mid-sagittal plane of the section) was marginal. As construction of a symmetric finite element model requires less time and effort, construction of an asymmetric model may be justified in special cases only

Effect of finite element model geometry on biomechanical parameters of the cervical spine

İnterspinus implantları, omurga stenosis ve faset artiritis gibi omurga patolojileri için kullanıldığı bilinir. Tasarımındaki ana düşünce spinos proseslere kuvvet uygulayarak birbirinden uzaklaştırmak ve klinisyenlerin kullandıkları günümüzde kullanılan Literatürde birçok servikal omurga sonlu eleman modellemesi bulunmaktadır. Birçoğu omurga modellini segital düzlemine göre simetrik olarak oluştursa da, modelin asimetrik örneklerini de görmekteyiz. Bu çalışmada her iki geometrideki omurga modeli ile biyomekanik parametreler değişik yüklenmeler altında incelenmiştir. Bu çalışmanın amacı, iki ayrı modelin, simetrik ve simetrik olmayan, biyomekanik parametrelerini karşılaştırmak ve geometrinin etkilerini incelemektir.Various finite element (FE) models of the cervical spine have been proposed in the literature. Most of the FE models assume that symmetry occurs about mid-sagittal plane while some other considers the accurate asymmetric geometry of the cervical spine. The proposed models are used to predict the motion response and internal biomechanics under different loading types. The aim of this paper is to investigate the influence of change in the geometry of the cervical spine on the predicted biomechanical parameters by the FE model

Motion analysis study on sensitivity of finite element model of the cervical spine to geometry

WOS: 000378421300009PubMed ID: 27107032Numerous finite element models of the cervical spine have been proposed, with exact geometry or with symmetric approximation in the geometry. However, few researches have investigated the sensitivity of predicted motion responses to the geometry of the cervical spine. The goal of this study was to evaluate the effect of symmetric assumption on the predicted motion by finite element model of the cervical spine. We developed two finite element models of the cervical spine C2-C7. One model was based on the exact geometry of the cervical spine (asymmetric model), whereas the other was symmetric (symmetric model) about the mid-sagittal plane. The predicted range of motion of both modelsmain and coupled motionswas compared with published experimental data for all motion planes under a full range of loads. The maximum differences between the asymmetric model and symmetric model predictions for the principal motion were 31%, 78%, and 126% for flexion-extension, right-left lateral bending, and right-left axial rotation, respectively. For flexion-extension and lateral bending, the minimum difference was 0%, whereas it was 2% for axial rotation. The maximum coupled motions predicted by the symmetric model were 1.5 degrees axial rotation and 3.6 degrees lateral bending, under applied lateral bending and axial rotation, respectively. Those coupled motions predicted by the asymmetric model were 1.6 degrees axial rotation and 4 degrees lateral bending, under applied lateral bending and axial rotation, respectively. In general, the predicted motion response of the cervical spine by the symmetric model was in the acceptable range and nonlinearity of the moment-rotation curve for the cervical spine was properly predicted.Scientific and Technological Research Council of Turkey [112M130]; American Hospital in IstanbulThe author(s) disclosed receipt of the following financial support for the research, authorship, and/or publication of this article: This study was supported by the Scientific and Technological Research Council of Turkey (no. 112M130) and the American Hospital in Istanbul

Servikal omurga biyomekaniğinde U-şeklindeki implantın etkisi

Fusion has been a standard method of treatment for decades as it tends to reduce or eliminate the pain at the operated segment. However, this method has a drawback that it results in the increase of stress and range of motion (ROM) at the adjacent levels. During the past few decades various implants have been modeled and tested to overcome the issue of adjacent level effects. Most of the implants have gone through various in vitro, in vivo and Finite Element (FE) studies. However, the U-Shaped implant for cervical spine has not been studied in such detail which motivated us to do FE analysis of U-Shaped implant. The goal of this study was to investigate the effect of a U-Shaped implant on the biomechanics of the cervical spine. The implant showed reasonable results for adjacent segments and maximum increase in ROM was 14 percent at C3-C4 level for lateral bending. But the results were not promising for restoration at the index level.Füzyon, ameliyat edilen bölgedeki ağrıyı azaltmaya veya yoketmeye eğilimi olduğu için yüzyıllardır standart bir metod olarak kullanılmaktadır. Fakat bu yöntem, yakın bölgelerde baskıyı ve gövde fleksiyon ve ekstensiyon (ROM) değerlerinin artışına neden olduğu için birtakım sakıncalar barındırmaktadır. Geçtiğimiz yıllar boyunca, çeşitli implantlar tasarlanmakta olup ve yakınlık düzeyinden kaynaklanan etkilerin üstesinden gelmek için test edilmektedirler. Implantların birçoğu çeşitli in vitro, in vivo ve sonlu eleman (FE) çalışmalarında kullanılmaktadır.Ancak servikal omurga için U-şeklindeki implantın henüz çok detaylı çalışılmamış olması, bizi U-şeklindeki implantın sonlu eleman (FE) analizini yapmaya teşvik etmiştir. İmplantın yakınında bulunan segmentler için mantıklı sonuçlar elde edilmiş olup, ROM değerlerindeki maksimum artış, C3-C4 seviyesinde yanal eğilmeler için yaklaşık olarak yuzde 14 artış göstermiştir. Ancak sonuçlar restorasyon için index seviyesinde çok belirgin sonuçlar göstermemiştir

Lumbar single-level dynamic stabilization with semi-rigid and full dynamic systems: A retrospective clinical and radiological analysis of 71 patients

WOS: 000411033200008PubMed ID: 28861198Background: This study compares the clinical and radiological results of three most commonly used dynamic stabilization systems in the field of orthopedic surgery. Methods: A total of 71 patients underwent single-level posterior transpedicular dynamic stabilization between 2011 and 2014 due to lumbar degenerative disc disease. Three different dynamic systems used include: (1) the Dynesys system; (2) a dynamic screw with a PEEK rod; and (3) a full dynamic system (a dynamic screw with a dynamic rod; BalanC). The mean patient age was 45.8 years. The mean follow-up was 29.7 months. Clinical and radiological data were obtained for each patient preoperatively and at 6, 12, and 24 months of follow-up. Results: Clinical outcomes were significantly improved in all patients. There were no significant differences in the radiological outcomes among the groups divided according to the system used. Screw loosening was detected in 2 patients, and 1 patient developed screw breakage. All patients with screw loosening or breakage underwent revision surgery. Conclusions: Each procedure offered satisfactory outcome regardless of which system was applied

Complications of 2-level dynamic stabilization: A correlative clinical and radiological analysis at two-year follow-up on 103 patients

WOS: 000443444000010PubMed ID: 30192368AIM: To investigate the postoperative complications, such as screw loosening, screw breakage and adjacent segment disease (ASD), in patients who underwent surgery with 2-level dynamic stabilization systems. MATERIAL and METHODS: Postoperative complications, clinical improvements and radiological parameters in patients who underwent surgery using a dynamic system for 2-level lumbar stabilization were retrospectively reviewed. A total of 103 patients with lumbar degenerative spinal instability underwent 2-level dynamic stabilization. Clinical findings were reviewed at 2-year follow-up. Screw breakage and loosening were evaluated during this duration together with clinical findings. RESULTS: Visual analog scale (VAS) and Oswestry Disability Index (ODI) scores were significantly decreased at the four-month evaluation, and they were also decreased at the 1-year follow up and at the 24th postoperative month. ASD was diagnosed in twelve (8 females, 4 males) of the 103 patients in the follow-up radiological and clinical controls. There were 9 screw breakages and 4 screw loosening cases. The complication rate of 2-level dynamic stabilization was high in this study. CONCLUSION: Our results showed that complications (screw loosening or breakage and adjacent segment disease) are not rare after 2-level dynamic stabilization, unlike the acceptable results with the single-level dynamic system. The most probable explanation is that the instrument system behaves more rigidly with every additional segment