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- 저자 : Nihat Acar (검색결과 4 건)
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The Mechanical Effect of Rod Contouring on Rod-Screw System Strength in Spine Fixation
Acar, Nihat,Karakasli, Ahmet,Karaarslan, Ahmet A.,Ozcanhan, Mehmet Hilal,Ertem, Fatih,Erduran, Mehmet The Korean Neurosurgical Society 2016 Journal of Korean neurosurgical society Vol.59 No.5
Objective : Rod-screw fixation systems are widely used for spinal instrumentation. Although many biomechanical studies on rod-screw systems have been carried out, but the effects of rod contouring on the construct strength is still not very well defined in the literature. This work examines the mechanical impact of straight, $20^{\circ}$ kyphotic, and $20^{\circ}$ lordotic rod contouring on rod-screw fixation systems, by forming a corpectomy model. Methods : The corpectomy groups were prepared using ultra-high molecular weight polyethylene samples. Non-destructive loads were applied during flexion/extension and torsion testing. Spine-loading conditions were simulated by load subjections of 100 N with a velocity of $5mm\;min^{-1}$, to ensure 8.4-Nm moment. For torsional loading, the corpectomy models were subjected to rotational displacement of $0.5^{\circ}\;s^{-1}$ to an end point of $5.0^{\circ}$, in a torsion testing machine. Results : Under both flexion and extension loading conditions the stiffness values for the lordotic rod-screw system were the highest. Under torsional loading conditions, the lordotic rod-screw system exhibited the highest torsional rigidity. Conclusion : We concluded that the lordotic rod-screw system was the most rigid among the systems tested and the risk of rod and screw failure is much higher in the kyphotic rod-screw systems. Further biomechanical studies should be attempted to compare between different rod kyphotic angles to minimize the kyphotic rod failure rate and to offer a more stable and rigid rod-screw construct models for surgical application in the kyphotic vertebrae.
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Nihat Acar 대한척추외과학회 2017 Asian Spine Journal Vol.11 No.4
Study Design: An experimental biomechanical study. Purpose: This study aims to investigate the behavior of a lamina injury in lumbar burst fractures during reduction maneuvers. Overview of Literature: Lumbar burst fractures are frequently accompanied by a lamina fracture. Many researchers concluded that any reduction maneuver will close the fractured lamina edges and possibly crush the entrapped neural elements. This conclusion did not rely on solid biomechanical trials and was based primarily on clinical experience. Methods: Eighteen fresh-frozen lamb spines were randomly divided into three groups. Using the preinjury and the dropped-mass technique, a burst fracture model was developed. A central laminectomy of 5 mm of the L3 lumbar spine was created to mimic a complete type of lamina fracture. To measure the movement of the fractured laminar edges, two holes were drilled on both sides of the upper and lower regions of the lamina to allow for optic marker placement. A single specific spine movement was applied to each group: traction, flexion, and extension. Gap changes were measured by camera extensometers. Results: After traction, the average values of the upper and lower aspects of the lamina interval showed narrowing of 1.65±0.82 mm and 1.97±1.14 mm, respectively. No statistical significance was detected between the two aspects. The upper and lower regions of the lamina gap behaved differently during extension. At 10°, 20°, and 30°, the upper part of the lamina interval was widened by an average of 0.016±0.024, 0.29±0.32, and 1.73±1.45 mm, respectively, whereas the lower part was narrowed by an average of 0.023±0.012, 0.47±0.038, and 1.94±1.46 mm, respectively. Conclusions: Neural element crushing may take place, particularly at the lower aspect of the fractured lamina gap during extension and throughout the whole lamina gap during traction. The lamina gap widens during flexion. Reduction maneuvers should be attempted after exploring the fractured lamina to prevent further neurological compromise.
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Openness and the Effects of Monetary Policy on the Exchange Rates: An Empirical Analysis
( Nihat Islk ),( Mustafa Acar ),( H. Bayram Islk ) 세종대학교 경제통합연구소 (구 세종대학교 국제경제연구소) 2005 Journal of Economic Integration Vol.20 No.1
This paper examines whether the effects of monetary policy on the exchange rates depend on the degree of openness of an economy. Theoretically, it can be shown that the effect of openness on the ability of money to influence the exchange rate is ambiguous. In light of this, the purpose of this study is to investigate how the relationship between monetary policy and exchange rate is affected by openness, hence shedding some light on the theoretical ambiguity. Using annual data for a panel of 41 countries for the period 1988-2000, the paper`s empirical results indicate that the effects of monetary policy on the exchange rates are negatively affected by economy`s openness. It seems that the more open the economy, the smaller is the depreciation effects of a given increase in the money growth rate. More interestingly, contrary to conventional expectations, monetary expansions in developed countries do not seem to result in depreciation of the domestic currency.
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Karakasli, Ahmet,Acar, Nihat,Uzun, Bora The Korean Neurosurgical Society 2018 Journal of Korean neurosurgical society Vol.61 No.2
Objective : Many lumbosacral fixation techniques have been described to offer a more screw-bone purchase. The forward anatomical fixation parallel to the endplate is still the most preferred method. Literature revealed little knowledge regarding the mechanical stability of lumbosacral trans-endplate fixation compared to the traditional trans-pedicular screw fixation method. The aim of this study is to assess the pull-out strength of lumbosacral screws penetrating the end plate and comparing it to the conventional trans-pedicular screw insertion method. Methods : Eight lumbar and eight sacral vertebrae, with average age 69.4 years, Left pedicles of the 5th lumbar vertebrae were used for trans-endplate screw fixation, group 1A, right pedicles were used for anatomical trans-pedicular screw fixation, group 1B. In the sacral vertebrae, the right side S1 pedicles were used for trans-endplate fixation, group 2A, left side pedicles were used for anatomical trans-pedicular screw fixation, group 2B. The biomechanical tests were performed using the axial compression testing machine. All tests were applied using 2 mm/min traction speed. Results : The average pull-out strength values of groups 1A and 1B were $403.78{\pm}11.71N$ and $306.26{\pm}17.55N$, respectively. A statistical significance was detected with p=0.012. The average pull-out strength values of groups 2A and 2B were $388.73{\pm}17.03N$ and $299.84{\pm}17.52N$, respectively. A statistical significance was detected with p=0.012. Conclusion : The trans-endplate lumbosacral fixation method is a trustable fixation method with a stronger screw-bone purchase and offer a good alternative for surgeons specially in patients with osteoporosis.
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