Role Of The Medial Canthus Fibrous Band In Forming Moderate And Severe Epicanthal Fold In Asians And Its Clinical Application

BackgroundThe epicanthal fold(EF),known as the Mongolian fold,refers to the semilunar flap located in the medial canthus.Because of its occlusion of the normal anatomical structure of the medial canthus,the appearance of the inner corner of the eye is rounded,which not only increases the distance between the inner canthus but also shortens the horizontal length of the eyelid fissure visually,so it greatly affects the beauty of the eye.About 40 %-60 % of Asians show EF appearance in adulthood.Single eyelid combined with congenital EF is a characteristic eyelid feature of Asians.The reason for special appearance of the eyelid is that the anatomical structure of the Asians is different from that of Caucasians.Although the etiology of EF is not clear,with the further study of eyelid anatomy,most scholars believe that EF is mainly related to the orbicularis oculi muscle and mixed fibers in the subcutaneous of EF now.However,there is no detailed description of the anatomical structure of the muscle and fiber in medial canthus area.And there is also no research report on the composition of the fiber structure in EF.Epicanthoplasty is the main treatment for congenital EF.Double eyelid surgery combined with epicanthoplasty is the most popular and accepted plastic surgery.At present,there are dozens of reports on epicanthoplasty methods.Among them,the flap method is the most widely used,which aims to release the local tension through the design and transposition of the flap to achieve the purpose of EF correction.However,there are still some limitations in either method for correcting moderate and severe EF.Especially for severe EF,due to the large local tissue tension of moderate and severe EF,postoperative complications such as scar residue,insufficient correction of EF or recurrence are still common.Therefore,finding the main cause of EF formation and removing subcutaneous tissue tension during epicanthoplasty are the key to reducing postoperative complications and improving patient satisfaction.Through the clinical work of epicanthoplasty in our department,we found that there is a dense fibrous tissue structure above the medial canthal tendon(MCT)in patients with moderate to severe EF.This structure may be a key factor in the etiology of EF,and also plays an important role in the formation of tension band in the inner canthus.We call it medial canthus fibrous band(MCFB).Objective1.To analyze the anatomical structure of MCFB and explore the relationship between MCFB and MCT,and its surrounding anatomical structure.2.The histological study of MCFB and MCT was performed to analyze and verify whether MCFB and MCT are the same anatomical structure.3.To explore the role of MCFB in the formation of EF.4.To explore the clinical application effect of MCFB excision method in epicanthoplasty.MethodsPart I: Anatomical study of MCFB in moderate and severe EF1.Dissect MCFB during epicanthoplasty and observe the relationship between MCFB and surrounding anatomical structures.2.The surgical videos of 40 patients who underwent double eyelid surgery combined with epicanthoplasty in our center from September 2019 to December 2022 were retrospectively analyzed.Measure the different meridian indexes of MCFB,including Area,transverse dimension(TD),vertical dimension(VD),upper eyelid direction length(UEDL),lower eyelid direction length(LEDL).Analyze whether there are differences in each meridian of MCFB between different degrees and different types of EF.Part II: Histological study of MCFB in moderate and severe EF1.From February 2020 to October 2021,we performed surgical sampling on 11patients(1 male patient,10 females,mean age 24.3 years)who underwent double eyelid surgery combined with epicanthus epicanthoplasty.The routinely discarded EF tissues(containing MCFB)in epicanthoplasty were embedded and sectioned.2.Special staining of tissue sections: HE staining,Masson trichrome staining,Weigert ’s staining.3.Immunohistochemical staining was performed on tissue sections and the differences in the composition of Collagen I,Collagen III and Elastin between MCFB and MCT and surrounding anatomical structures were analyzed.Part III: Clinical study of MCFB in moderate and severe epicanthoplasty1.Review 37 patients with moderate to severe EF who underwent MCFB excision technique epicanthoplasty in our department from February 2020 to October2021.The patients were followed up at 1 month,3 months,6 months and 12 months after operation.2.The tension of the medial canthus area released by MCFB excision was evaluated by comparing the preoperative exposed lacrimal caruncle area(Pre.-ELCA)and immediate exposed lacrimal caruncle area(Immed.-ELCA)after resection of MCFB.3.The intercanthal distance(ICD)and horizontal lid fissure length(HLFL)were measured by Image J software before and 6 months after operation.At the same time,the ratio of ICD to HLFL(ICD / HLFL)was also calculated to evaluate the cosmetic effect of MCFB excision technique epicanthoplasty.4.The Patient and Observer Scar Assessment Scale(POSAS)was used to evaluate the postoperative scar recovery of patients underwent MCFB excision technique epicanthoplasty at 1 month,3 months,6 months and 12 months after surgery respectively.ResultsPart I: Anatomical study of MCFB in moderate and severe EF1.MCFB is a fibrous band structure with thickening in the inner canthus of moderate and severe EF,and has the following anatomical characteristics:(1)MCFB is located below the EF skin at the inner canthus,and the top surface of MCFB is closely adhered to the posterior wall skin of the EF;(2)There is a close fusion point between MCFB and MCT near the inner canthus of the lacrimal lake,and the boundary between the two cannot be distinguished by the naked eye.(3)When MCFB goes to the nasal side,there is no close fusion between MCFB and MCT,but there is a mixture of muscle fibers.2.The size of MCFB was positively correlated with the severity of the EF: the meridian lines of MCFB in severe EF were larger than those in moderate EF(P< 0.01).The LEDL of MCFB in severe EF was longer than that of UEDL(P< 0.01).The LEDL of epicanthus tarsalis type in EF with the same degree and different types of EF was larger than that of epicanthus palpebralis type(P< 0.01).Part II: Histological study of MCFB in moderate and severe EF1.The fiber orientation between MCFB and MCT is different.2.The MCFB and MCT were connected by a fusion site(FS)of dense fiber points at the inner canthus near the lacrimal lake.The fiber orientation between MCFB and FS is different.3.The MOD value of Collagen I in MCFB was lower than that in FS and MCT and the difference was statistically significant(P< 0.001),while the MOD value of Collagen I in FS and MCT was not statistically different.4.In the protein analysis of Collagen III,the content of Collagen III in MCFB was the least,followed by MCT;the content of FS was the highest,and the three groups of data were statistically different from each other(P< 0.05).5.The distribution of Elastin content was consistent with Weigert ’s staining results,that is,FS>MCFB>MCT,and there were statistical differences between the three groups(P< 0.05).Part III: Clinical study of MCFB in moderate and severe epicanthoplasty1.MCFB was the tension anchor of EF: the lacrimal caruncle was exposed immediately after resection of MCFB,and Immed.-ELCA was significantly higher than Pre.-ELCA(P<0.001).2.The cosmetic effect of MCFB excision technique epicanthoplasty was good: the ICD after operation was significantly smaller than that before operation,P< 0.001;postoperative HLFL increased compared with preoperative,P< 0.001.At the same time,the postoperative ICD/HLFL was significantly lower than that before surgery,P< 0.001.The postoperative ICD/HLFL was between 1-1.2,which met the aesthetic definition.3.MCFB excision technique epicanthoplasty postoperative scar recovery is good:using this technique,postoperative scar score in the overall degree is low.At one month after operation,PSAS,OSAS,overall score of patients and observers were the highest.The scores decreased significantly at 3 months,6 months and 12 months after operation(P< 0.001).There was no significant difference in the scores between 3 months after operation and 6 months and 12 months after operation,but the overall score of the observer at 3 months after operation was higher than that at 12 months after operation.4.In the follow-up observation of this study,no traumatic complications such as hematoma,infection,lacrimal canaliculus injury and MCT injury occurred.Conclusions1.MCFB is a fibrous band structure in the inner canthus of moderate to severe epicanthus,which play an important role in the formation of EF.2.MCFB and MCT are two anatomical structures with different fiber orientation and different collagen and elastin contents.3.MCFB and MCT are two anatomical structures with different fiber orientation and histological composition.The two are fused at the inner canthus point.4.MCFB is the tension anchor point of the OOM at the inner canthus.MCFB excision technique epicanthoplasty can effectively relieve the tension of inner canthus,and the recurrence rate is low.