Digital Analysis Of The Zygomatic Asymmetry Correction With L-shaped Reduction Malarplasty For Hemifacial Microsomia

Objectives1.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 miceosorrmia with L-shaped reduction malarplasty.To analyze the feasibility about evaluating the surgical outcome by the movment of the summit of zygoma.Methods1.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.Results1.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.Conclusions1.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.