髁突矢状骨折单板与平行双板坚固内固定生物力学分析

Biomechanical Analysis on Fixation Sagittal Fracture of the Mandibular Condyle with Single Plate or Double Parallel Plates

目的以生物力学角度对比单板与平行双板法治疗髁突矢状骨折(Sagittal Fracture of the Mandibular Condyle,SFMC)两种坚固内固定方式,为治疗SFMC提供依据。方法以三维有限元法(finite element analysis,FEA)建立包含双侧髁突的下颌骨的有限元模型。设右侧髁突为骨折侧,用厚0.1mm的薄层模拟骨折裂隙,建立单板、平行双板坚固内固定三维有限元模型。计算不同接骨板固定方式固定后下颌骨整体的应力分布状况和骨折侧髁突表面的应力分布、骨折断端的位移、微型钛板的受力、应力遮挡的状况。结果 (1)右侧髁突的最大等效应力为97.176 MPa,最大总位移为0.342mm,最大总转角为0.031°。(2)单板固定方式中,钛板的髁突残端固定处受力达2297MPa;髁突总体位移为0.9123mm;髁突游离端下部最大应力达243MPa,最大位移与最大转角分别为0.8794mm与0.0375°。(3)平行双板固定方式中,髁突残端所受应力为525.475MPa;髁突产生总体位移为0.9022mm;髁突游离端最大等效应力4.425 MPa,最大总位移0.8827mm,最大总转角0.0199°,接骨板最大等效应力为530.324 MPa。结论 (1)单板法中,接骨板所产生的应力遮挡作用会导致髁突游离端明显移位,从而造成错位愈合,增加髁突改建程度。(2)平行双板法中,接骨板及髁突所承受的应力与正常髁突所承受的应力相似,接骨板的应力遮挡作用致髁突游离端移位程度也明显减小,减少术后错位愈合,减少相关并发症的发生。

Objective To analyze the biomechanical stress distribution on fixation sagittal fracture of the man- dibular condyle （SFMC） with single or double parallel plates, and to obtain a proper way from the two fixation methods for surgical treatment SFMC. Methods The finite element model of mandible and condyle was es- tablished. The right condyle was simulated as SFMC with 0. l mm space across the condyle lengthways. The fixation finite element models with single plate or double parallel plates were established. The biomechanical stresses on mandible and condyle were calculated with finite element analysis （FEA）. There were stress distri- bution of condylar surface, displacement around fi＇acture, stress on the plate and stress shielding. Results （1） Maximum equivalent stress, maximum total displacement and maximum total comer were 97. 176MPa, 0. 342mm and 0. 031 degree respectively on right condyle. （2） Single plate： the stress on plate was 2297 MPa; total condylar displacement was 0. 9123mm, the maximum stress on fractured fragment of condyle was 243 MPa, maximum displacement was 0. 8794mm, maximum total comer was 0. 0375 degree. （3） Double parallel plates： the stress on condyle was 525. 475MPa, the total displacement of condyle was 0. 9022mm, maximum equivalent stress on fractured fragment was 4. 425MPa, maximum total displacement was 0. 8827mm, maximum total comer was 0. 0199 degree, and maximum equivalent stress on plate was 530. 324MPa. Conclusions （ 1 ） The fractured fragment of condyle may shift from its fixation place under the action of stress shielding on the plate when single plate is used to fixation SFMC. And the same time, the stress shielding may lead to dislocation healing and deformation of condyle in SFMC. （2） The stress action on plate and condyle is similar with that in normal condyle when double parallel plates are used to fixation SFMC. The stress shielding is not easy to dislocation healing and condylar deformation because of proper stress.