目的

1. 分析颧骨"L"型截骨降低术中骨块移动与截骨线及截骨面方向的关系，分析如何通过截骨线（面）的合理设计减少术后面部下垂及骨不连等并发症的发生率，为手术设计和实施提供参考。

2. 分析半侧颜面短小畸形患者双侧颧骨颧弓不对称的特点，对其颧骨颧弓发育不良的特征进行分型并行CT测量比较两侧差异，为临床治疗其不对称的手术设计提供参考。

3. 回顾性分析应用颧骨"L"型截骨降低术改善半侧颜面短小畸形患者颧骨不对称的手术效果，评价手术后颧面部对称性的改善程度及应用颧突点变化描述手术效果的可行性。

方法

1. 通过将颧骨"L"型截骨降低术中骨表面的截骨线投影至冠状面后调整截骨线不同倾斜角度建立四个模型，分析各模型截骨后骨块移动差异。通过CT三维重建设计不同截骨面方向，模拟骨块移动后分析颧骨复合体移动与截骨面方向关系,观察骨块移动后的骨质接触情况。

2. 通过重建半侧颜面短小畸形患者头颅三维CT图像，观察颧骨颧弓形态特点并根据其特点提出半侧颜面短小畸形患者颧骨颧弓发育不良的三度五分法。分析颧骨颧弓发育不良各分型与下颌骨发育不良Pruzansky分型关系。结合CT断层图像及三维重建图像提出针对半侧颜面短小畸形患者颧骨颧弓测量的坐标系建立及颧突点定位方法，测量分析双侧颧骨突度、宽度、高低位置等差异，并比较本研究所采用方法定位颧突点与前人文献方法定位颧突点差异。

3. 对2012年10月至2016年10月期间就诊我中心并行颧骨"L"型截骨降低术改善颧骨不对称的半侧颜面短小畸形患者进行回顾性研究，通过手术前后CT断层图像及三维重建图像测量分析颧骨各测量指标手术前后差异。应用三维配准法观察手术前后两侧颧骨对称度差异。比较手术前骨性颧突点与软组织颧突点距各平面距离分析两者位置关系，比较手术前后骨组织颧突点位置变化与软组织颧突点位置变化,分析两者关系。

结果

1. 颧骨"L"型截骨降低术几何学分析示颧骨复合体下移的量与颧骨内收量及长臂截骨线与水平面的夹角呈正相关，颧骨复合体内收的量与颧骨截除骨块宽度有关但并不一定完全相等。CT三维重建模拟两个不同倾斜角度长臂截骨面截骨后骨块移动分析示颧骨复合体在垂直方向上移动距离有统计学差异，长臂截骨面越向下倾斜则骨块向下移动距离越大。CT三维重建模拟五个不同倾斜角度短臂截骨面截骨后骨块移动分析示在颧骨前表面截骨宽度相等的条件下，不同内侧短臂截骨面方向模型之间颧骨复合体各方向移动距离存在统计学差异。观察骨块移动后内侧骨面的接触情况示截除骨块呈现前宽后窄倒梯形时可能实现骨块完全接触。

2. 85例半侧颜面短小畸形患者颧骨颧弓发育不良形态三度五分法分型与下颌骨发育不良Pruzansky分型无绝对对应关系。84例患者两侧测量结果配对t检验示SOZ-O、SOZ-X、SOZ-Y、SOZ-FP、zy-Y、zy-FP、FMSM/zy-Y等七项指标两侧有统计学差异，而FMSM两侧无统计学差异。颧骨颧弓发育不良各分型患者颧骨颧弓两侧测量结果配对t检验示IIA型患者zy-Y及FMSM/zy-Y两侧无统计学差异。本研究采用方法与前人方法所定位颧突点至各平面距离配对t检验均无统计学差异。

3. 23例行颧骨"L"型截骨降低术的半侧颜面短小畸形患者手术前后骨性颧突点至各平面测量参数变化均有统计学差异，手术后两侧颧骨前外侧对称性较术前增加,手术前后颧弓点位置变化不大，手术后面宽对称性改善有限。软组织颧突点与骨组织颧突点至各平面距离不一致，手术前后软组织颧突点位置变化与骨组织颧突点至各平面距离变化不完全一致。

结论

1. 颧骨"L"型截骨降低术中长臂截骨线或面越倾斜则术后颧骨复合体下移的量越大，继而导致术后面部下垂增加。短臂截骨线或面的方向影响颧骨复合体内收的量，当截除骨块呈前宽后窄时可能达到内侧骨面完全接触，有利于骨质愈合，减少术后骨不连的发生。

2. 本研究采用半侧颜面短小畸形患者头面部测量坐标系设定及颧突点定位方法准确性及重复性好。本研究采用半侧颜面短小畸形患者颧骨颧弓发育不良分度分型方法简单易用，但临床实用性有待验证。大部分半侧颜面短小畸形患者患侧颧骨突度小于健侧、颧突点位置高于健侧、患侧面宽小于健侧，但亦存在患侧颧骨较健侧突出的特例，手术方案选择时应予注意。

3. 颧骨"L"型截骨降低术可有效改善半侧颜面短小畸形患者颧骨前外侧对称性，该手术对面宽改善有限，针对健侧面宽大于患侧的患者可同时施行颧弓截骨内收术。术后原骨性颧突点内收后移，新的骨性颧突点位于长臂截骨线上方。颧突点位置变化与颧骨复合体移动不一致，以手术前后骨组织颧突点位置变化评估手术效果的方法准确性值得商榷。

Objectives

1. To analyze the relationships between the orientation of the osteotomy lines(planes) and the movement of the zygomatic complex. To study the strategy to diminish the complication of dropping and bone nonunion by the reasonable designment of the osteotomy lines and planes.

2. To study the difference between the bilateral zygoma for patientes with hemifacial microsomia.Try to put forward a simple and practical classification of the zygoma and zygomatic arch hypoplasia for patients with hemifacial microsomia, compare the difference of the zygoma on both sides with CT measurement.

3. To analyze the surgical outcomes of the correction of zygomatic asymmetry caused by hemifacial miceosomia with L-shaped reduction malarplasty. To analyze the feasibility about evaluating the surgical outcome by the movment of the summit of zygoma.

Methods

1. Project the osteotomy lines of the L-shaped reduction malarplasty to the coronal plane and establish four models of osteotomy by adjusting the orientation of the osteotomy lines. Analyze the difference about bone movement between four models. Models with different osteotomy planes were set up on three dimensional CT images, analysis about the difference of bone movement and bone contact between each models were made.

2. A simple classification of the zygoma and zygomatic arch hypoplasia with three grades and totally five substates were posed. The possible relationship between the zygoma classification and the mandibular hypoplasia Pruzansky classification was analyze. A coordinate system and a zygomatic summit positioning method were proposed. Difference quantities about the position of the bilateral zygomatic summits were analyzed based on the measurements on CT slice images and CT three-dimensional reconstruction images.

3. A retrospective study was conducted, patients with hemifacial microsomia who received L-shaped reduction malarplasty in our center from October 2012 to October 2016 were included in the study. Changes of the bony parameters and the symmetry ascension of the zygomatic complex were evaluated base on CT slice images and CT three-dimensional reconstruction images. The relationship between bony zygomatic summit and the most protruding point of the soft tissue in the zygomatic area was also analyzed.

Results

1. The geometry analysis showed the inclination of the oblique osteotomy line and the adduction of the zygomatic complex are the two factors positively correlated with the downward movement of zygomatic complex. Significant differences of the zygomatic complex bone movement on diferent directions were seen between each models set up on three dimensional CT images. Bone block contact completely can be achieved when the bone removed is with the shape of inverted trapezoidal on the anterior-posterior direction.

2. No absolute corresponding relationship between the zygomatic hypoplasia classification and the mandibular hypoplasia Pruzansky classification was found on 85 patients. Significant differences of the malar bony measurements excepted for a metrics of FMSM were found between the affected side and the normal side in 84 patients. No significant bilateral differences on the metrics of the zy-Y and FMSM/zy-Y were found in patients with a IIA type zygomatic hypoplasia classification. No significant differences was found between the position of the zygomatic summit located by the method used in this study and by previous reports.

3. The symmetry of the anterolateral part of the zygomatic complex was significantly improved and the symmetry of the midface width changed finite after the operation of L-shaped reduction malayplasty was performed. The position of the bony zygomatic summit and the most protrud soft tissue point in the zygomatic area was no the same. Movement of the two points was not equal.

Conclusions

1. The orientation of the long arm osteotomy line(plane) affects the dropping of the zygomatic complex while the orientation of the short arm osteotomy lines(planes) influence the zygomatic complex adduction. The more oblique the long arm ostertomy line(planes) is ,the more likely of the bone move downward and postoperative facial dropping would be occurred. A completely contact of the Bone block and a lower incidence of postoperative bone nonunion can be achieved when the bone removed is with the shape of inverted trapezoidal on the anterior-posterior direction.

2. The coordinate system and the zygomatic summit locating method are with good accuracy and repeatability. The zygomatic hypoplasia classification index is simple and easy to use, but the utility of this classification still need to be verified in clinic.  A minor phenotype of the zygoma and a higher position of the zygomatic summit and a narrower midface width are likely to appear on the affected side in most of the patients with hemifacial microsomia. But there are also some exceptions whose zygoma on the affect side are more protrude than the normal side, attention should be paied when making the operation plan.

3. The operation of L-shaped reduction malayplasty improves the symmetry of the anterolateral part of the zygomatic complex significantly, but the midface width changed finite. A simultaneously operation of zygomatic arch adduction should be taken into sonsideration for patients with a significant differece on the midface width. The zygomatic complex including the original zygomatic summit adducts during the operation of L-shaped reduction malarplasty, a new zygomatic summit shows above the oblique ostoeotomy line. The change of the position of the zygomatic summit and the zygomatic complex movement are inconsistent. The accuracy of assessing the operation outcome with the position change of the zygomatic summit is questionable.