有限元法分析儿童发育不良髋关节“人”字型固定后的应力特征

Stress characteristics after fixation in herringbone position in children with developmental dislocation of the hip by finite element analysis

背景:目前对于儿童发育性髋关节发育不良患者复位后固定的体位有很大争议,虽然大家公认髋关节的外展角度大有助于复位后关节稳定,但外展角度越大,生物力越异常,股骨头髋臼间压力越大,进而容易引起股骨头坏死。当前"人"字型固定是临床常用的固定体位,但其生物力到底如何分布尚不明确。目的:利用有限元分析方法,研究发育性髋关节发育不良患儿在"人"字型固定后髋关节的生物力分布情况,探讨临床合理的固定体位。方法:选取1例来沈阳医学院附属中心医院就诊的单侧发育性髋关节发育不良患儿骨盆和股骨近端原始CT数据,导入Mimics15.0软件,经区域增长、编辑笼罩、光滑、包裹等处理重建双侧髋关节三维有限元模型,并在Hypermesh12.0软件中进行网格划分、定义材料属性、设定边界条件、加载负荷,模拟"人"字型固定时髋关节体位及受力情况进行三维有限元计算分析。得到骨盆、髋臼和股骨近端的VonMises应力分布云图和力学位移云图,评价力学云图特点并计算出股骨头与髋臼间的平均接触压力,最大接触压力和接触面积。结果与结论:①"人"字型固定时脱位侧的股骨头髋臼间平均接触压力、最大接触压力及股骨头所受VonMisas应力峰值都高于未脱位侧,头臼接触面积小于未脱位侧,头臼接触面积、最大接触压力和股骨头所受VonMisas应力峰值比较差异有显著性意义(P<0.05);②结果证实,对发育性髋关节发育不良患儿而言,静态的"人"字型固定时脱位侧髋关节生物力分布异常,股骨头臼间存在较高压力,容易股骨头坏死。试验方案已经于2018年通过沈阳医学院附属中心医院医学道德伦理委员会批准(批准号:20180987)。

BACKGROUND: The fixed position after reduction of the children developmental dislocation of the hipremains controversial. Large abduction angle of the hip joint has been shown to contribute to the joint stability after reduction, but larger abduction angle will cause abnormal biomechanics, and high pressure in the acetabulum, thus further inducing femoral head necrosis. Herringbone position is commonly used in clinical practice, but its biomechanical properties are unclear. OBJECTIVE: To investigate the stress distribution of the hip joint after fixation in herringbone position in children developmental dislocation of the hip by finite element analysis, and to explore the optimal position in clinic. METHODS: The CT data of pelvis and proximal femur were collected from a patient with unilateral developmental dislocation of the hip at the Central Hospital of Shenyang Medical College, and imported into Mimics 15.0 software to reconstruct the three-dimensional finite element model of bilateral hip joints after region growing, editing, smoothing and wrapping. Meshing, material property definition, boundary setting and loading were conducted on Hypermesh 12.0 software to simulate hip joint fixed in herringbone position and calculate the stress distribution. The Von Mises stress distribution and mechanical displacement nephograms of pelvis, acetabulum and proximal femur were obtained, the mechanical properties were evaluated. The average contact pressure between femoral head and acetabulum, maximal contact pressure, and contact area were calculated. RESULTS AND CONCLUSION:(1) After fixed in the herringbone position, the average contact pressure between femoral head and acetabulum, maximal contact pressure, and maximal Von Misas value of the femoral head at the affected side were higher than those at the unaffected side, and the contact area at the affected sided was lower than that at the unaffected side. The contact area, maximal contact pressure, and maximal Von Misas value of the femoral head showed significant differences(P < 0.05).(2) To conclude, for children with developmental dislocation of the hip, abnormal biomechanical distribution occurs on the affected hip joint after fixed in the herringbone position, and high pressure between femoral head and acetabulum is easy to induce femoral head necrosis. This trial was approved by the Medical Ethics Committee, the Central Hospital of Shenyang Medical College in 2018(approval No. 20180987).