Protsenko Dmitriy E, Wong Brian J F
Annu Int Conf IEEE Eng Med Biol Soc. 2007;2007:5399-402. doi: 10.1109/IEMBS.2007.4353563.
Successful application of laser cartilage reshaping (LCR) for the in-situ treatment of structural deformities in the nasal septum has generated increasing clinical interest, because septoplasty is among the top five most common operations performed. However, few studies have investigated stress fields existing in the nasal septal cartilage during LCR of septal deviations. The objectives of this study were to: (1) formulate a finite-element model describing stress fields in mechanically straightened septum, (2) calculate stress fields in the septum after a given pattern of laser irradiation produced thermally induced stress relaxation in selected sites, and (3) investigate the dependence of the overall stress relaxation in a straightened septum as a function of the number, location and size of laser irradiation sites.
The cartilagenous nasal septum was modeled as 24 x 24 x 1.5 mm slab. The deviation was represented as a bulge in the center of the septum with a maximum elevation above the surface of 2 mm. A straightening deformation was represented in form of displacement boundary condition applied to the bulge. Laser irradiation applied in a rectangular pattern of several spots was assumed. The effect of thermally induced stress relaxation was modeled as a simultaneous change in the cartilage mechanical properties and reduction of strain occurring within irradiated spots according to the heating history. The finite-element method was used to calculate stress fields within the straightened septum and the force of reaction to the straightening deformation before and after laser irradiation.
Straightening deformation produced a highly non-homogeneous stress field with both regions of tension and compression present. Reaction force decreased with increasing number of irradiation sites and delivered laser energy. The model predicts that laser irradiation reducing reaction force by approximately 95% results in approximately 50% thermal damage to septal cartilage.
A numerical model of stress fields in laser-reshaped deviated septum has been developed. The model shows highly non-homogeneous stress distributions before and after laser treatment. The model predicts that sufficiently high reduction of reaction force can be obtained with a localized laser treatment.
激光软骨重塑术（LCR）在鼻中隔结构畸形原位治疗中的成功应用引发了越来越多的临床关注，因为鼻中隔成形术是最常见的五大手术之一。然而，很少有研究调查鼻中隔偏曲的激光软骨重塑过程中鼻中隔软骨内存在的应力场。本研究的目的是：（1）建立一个描述机械矫正后鼻中隔应力场的有限元模型；（2）计算在选定部位进行特定模式的激光照射产生热诱导应力松弛后鼻中隔内的应力场；（3）研究矫正后鼻中隔整体应力松弛对激光照射部位数量、位置和大小的依赖性。
将鼻中隔软骨建模为24×24×1.5mm的平板。鼻中隔偏曲表现为鼻中隔中央的一个凸起，其高于表面的最大高度为2mm。通过对凸起施加位移边界条件来表示矫正变形。假设以多个点的矩形模式进行激光照射。热诱导应力松弛的影响通过根据加热历史同时改变软骨力学性能以及减少照射部位内发生的应变来建模。采用有限元方法计算矫正后鼻中隔内的应力场以及激光照射前后对矫正变形的反作用力。
矫正变形产生了一个高度不均匀的应力场，同时存在拉伸和压缩区域。反作用力随着照射部位数量和传递的激光能量增加而降低。该模型预测，激光照射使反作用力降低约95%会导致鼻中隔软骨约50%的热损伤。
已建立激光重塑偏曲鼻中隔应力场的数值模型。该模型显示激光治疗前后应力分布高度不均匀。该模型预测，通过局部激光治疗可获得足够高的反作用力降低。
