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Öğe Biomechanical study on three screw-based atlantoaxial fixation techniques: A finite element study(Korean Society of Spine Surgery, 2022) Erbulut, Deniz Ufuk; Mumtaz, Muzammil; Zafarparandeh, Iman; Özer, Ali FahirStudy 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.Öğe Investigation into cervical spine biomechanics following single, multilevel and hybrid disc replacement surgery with dynamic cervical implant and fusion: A finite element study(Multidisciplinary Digital Publishing Institute (MDPI), 2022) Mumtaz, Muzammil; Zafarparandeh, Iman; Erbulut, Deniz UfukCervical 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.Öğe Motion analysis study on sensitivity of finite element model of the cervical spine to geometry(SAGE Publishing Ltd, 2016) Zafarparandeh, Iman; Erbulut, Deniz Ufuk; Özer, Ali FahirNumerous 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.Öğe Servikal omurga sonlu eleman modellemesinde, model geometrisinin biyomekanik parametrelere olan etkisi(Institute of Electrical and Electronics Engineers, 2015) Zafarparandeh, Iman; Erbulut, Deniz Ufuk; Özer, Ali Fahirİnterspinus 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.
