Advances in research on factors of cranioauricular angle formation after auricular reconstruction

Peng WANG,Li-kun ZHU,Yong-jing HE,Xiao-xiao TAN,Ji-hua WANG

Department of Plastic Surgery,Second Affiliated Hospital,Kunming Medical University,Kunming City,Yunnan Province,650101,China

ABSTRACT Objective To review the advances in research on factors of cranioauricular angle formation after auricular reconstruction.Methods The related literature concerning the main surgical methods and influencing factors for the ear elevation by Nataga method and dilated method was reviewed and summarized.Results The ear elevation by Nataga method and dilated method has achieved satisfactory clinical results.Although rapid prototyping technology and tissue engineering have developed rapidly,it is still some time before a beautiful and practical cranioauricular angle can be reconstructed.Conclusion The surgical programs for ear elevation by Nataga method and dilated method have been constantly improved in recent years,which provides a great deal of reference for obtaining a beautiful and practical cranioauricular angle.

KEY WORDS Nataga method;Dilated method;Auricle reconstruction;Cranioauricular angle;Ear elevation;Influencing factors

PREFACE

The normal auricles are located on both sides of the skull and are bilaterally symmetrical.The upper end is flush with the horizontal line on the eyebrow,and the lower end is located on the horizontal line passing through the bottom of the nose.It is about 30°～45° with the cranial side wall[1].However,the loss of auricle not only affects the quality of life and normal socialization of patients,but also causes abnormal psychological development[2].It is necessary to recreate a realistic three-dimensional auricle,which is more challenging for clinicians.After decades of development,although the technology of auricle reconstruction is becoming more and more mature,how to reconstruct a cranial and auricular horn with aesthetic and practical functions has always been a problem that clinicians need to explore and solve.On the review of related literatures,the current research progress on the main autologous costal cartilage auricle reconstruction,ear elevation and the related influencing factors are summarized as follows.

THE MAIN METHOD OF AUTOLOGOUS COSTAL CARTILAGE AURICULAR RECONSTRUCTION

Nataga Method For Auricle Reconstruction

That is,the reconstruction of the costal cartilage stent in the mastoid region,was first proposed by Nagata in Japan in 1991[3].The method is divided into two phases:in the first stage,the ear stent carved by the costal cartilage is directly implanted under the skin of the ear,and the earlobe transposition and the papillary region flap are covered.At the interval of 3-6 months,the second stage of the ear elevation is performed,that is,the crescent cartilage is implanted behind the ear support and the fascia flap is used to cover the skin graft to form the cranioauricular angle.This method does not require the implantation of a dilator,and has become one of the main methods for the treatment of congenital microtia.

Dilated Method For Auricle Reconstruction

The dilated method by using the expander and autogenous rib cartilage for ear reconstruction is the use of skin soft tissue expansion technology to pre-expansion of the local skin,the second phase of the implantation of the cartilage stent.Since the introduction of the dilator into China in 1984,domestic scholars[4]have begun to explore the expansion of the ear reconstruction.According to the different expansion schemes,they can be divided into two categories:the expansion flaps to cover the anterior surface of the cartilage scaffold,that is “partial expansion of the ear reconstruction” and the “completely expanded ear reconstruction” includes the expansion flaps to cover the front and back surfaces of cartilage scaffold,no need to replant the skin after the ear,and the completely expanded auricular reconstruction with the cranioauricular angle forming once.

EAR ELEVATION

Different methods of auricular reconstruction,in the end,must form a symmetrical skull angle between the auricle and the cranial wall,that is,ear elevation.Now,In view of the two major methods of the current reconstruction of auricular auricles,the progress of the formation of the cranioauricular angle is highlighted as follows.

Nagata Method for Ear Elevation

By reading the relevant literature,we learned that after the Nagata method,the cranioauricular angle formation was originally implanted with costal cartilage or artificial material under the ear support,and now it is lining under the ear support through the free reflexed cushion of the residual ear cartilage fascia flap.There are also two-valve composite skin grafting to create auriculocephalic angle,etc.The methods are not the same,each has its own advantages and disadvantages[5].In order to achieve the ideal cranioauricular angle,many scholars have made more improvements in the creating auriculocephalic angle.The differences are mainly reflected in four aspects:the support material behind the ear,the fascia flap covering the ear support,and the type of the skin and flap method.

Post-ear support scaffold material

Nagata[6]reported in 1994 the application of crescentshaped costal cartilage as a support material for the posterior support of the ear.The height of the crescentshaped cartilage is 1 to 1.2 cm,which can effectively maintainthecranioauricular angleofreconstructedear.Later,XuFeng etal[7],Liang Jiulongetal[8]reportedthat the crescent-shaped cartilage inside was changed into a chevron shape,which is more in line with the anatomical features of the cranioauricular angle and less prone to slide,shift,or even flip.However,the costal cartilage itself has a certain elasticity and needs more costal cartilage as support to form a satisfactory cranioauricular angle.Excessive excision of costal cartilage will lead to an increased incidence of thoracic malformation.In addition,the costal cartilage may partially absorb under the stress stimulation of scar contracture,resulting in smaller cranioauricular angle after surgery.Therefore,the application of artificial materials as support becomes a new research direction.Tai et al[9]reported in 2006 the application of hydroxyapatite tricalcium phosphate composite bioceramics and Romo et al[10]reported in 2008 using high-density porous polyethylene (Medpor)as the material of posterior auricular support,satisfactory reconstructed auricle shapes were obtained.Zhang et al[11]reported in 2009 the use of hydroxyapatite composite epoxy acrylate maleic acid material as a support scaffold to obtain a satisfactory shape of the cranioauricular angle.Du Xiaoyang et al[12]reported in 2011 that a solid silicone rubber engraved into a crescent shape was placed behind the seat of the costal cartilage stent as a support for the skull angle,and pointed out that the solid silicone rubber was more flexible than the Medpor material and was easy to engrave and cheap,which was a good choice for the support of the posterior ear in the ear reconstruction of the second stage of the ear elevation.Li et al[13]reported in 2012 to design a special shape titanium mesh device that can be fixed on the mastoid bone and ear cartilage skeleton as a post-ear support material,which can achieve stable elevation angle and stable front projection,and create A natural cranial ear appearance.Zheng Shengwu et al[14]reported in 2017 the application of medical resin and hydroxyapatite composite artificial bone instead of costal cartilage as a post-auricular support material,and achieved good postoperative results.

Fascia flap covering the ear stent

In cranioauroplasty,the blood supply and variation of the fascia surrounding the posterior auricular support stent and the auricle stent should be fully considered.The selection of fascia flap is still a hot topic among scholars.Currently,there are two types of fascia selection:the superficial fascia and the posterior fascia.The former blood supply originates from the superficial temporal artery and its branches,and the latter comes from the posterior ear artery and the superficial temporal artery.Nagata[3]In the formation of cranioauricular angle,the posterior support bracket and the auricle stent were coated with the superficial temporal fascia flap,and satisfactory results were obtained.Since then,Firmin[15],Chen[16]and Wang Meishui et al[17]have also reported good results with the use of superficial fascia wrapped stents.The superficial temporal fascia overlaying was superior to Weerda[18]’s retro-occipital fascia flap overlaying in maintaining the shape and depth of the auricular sulcus,and the blood supply of superficial temporal fascia was superior to that of posterior occipital fascia.However,Brent[19],Tai[9],Cho[20-21]and Zhang[11]reported that the posterior auricular fascia flap was used to invert and subwrap the stent,and satisfactory postoperative results were obtained.Jin Peihong et al[22]compared the effect of superficial temporal fascia flap and posterior fascial flap in ear elevation,indicating that the repair effect of the posterior fascia is better than that of the superficial fascia.Chu Yanjun et al[23]also confirmed the application of the posterior fascial flap to cover the ear stent and achieved satisfactory results.It is believed that the blood supply of the posterior fascial flap is more stable than that of the superficial temporal fascia flap,which is more suitable for ear elevation.Zheng Shengwu et al[14]reported the experience of applying the posterior fascia flap is:the posterior fascia flap should be wide enough,the width from the outer edge of the lug is about 2.0～3.5cm,after flipping The fascial flap is a standard for tension-free adherence covering the posterior support bracket and re-establishing the auricular stent.At the same time,the advantages of using this valve were also proposed:the incision of the posterior auricular fascia flap did not need to increase the temporal incision,and the complications of temporal incision scar and hair loss were avoided.The anatomy and turnover of the posterior ear fascia are relatively simple,which can shorten the time of operation and anesthesia.If a large range of stent exposure complications occur after auricle reconstruction,it is often difficult to deal with,so the superficial temporal fascia is retained as the tissue significance of repairing stent exposure complications.

Types of skin and source

The surface of the fascial flap and the surface of the mastoid area need to be skinned for repair.It can be transplanted with full thickness or segmented skin.The donor area has a post-ear ear mastoid area and a chest wall costal cartilage incision.The disadvantage of the area,the groin area,and the scalp is that the donor area will leave scars.Xu Feng et al[7]took the free skin piece behind the healthy ear to cover the wound after the ear,and took the free skin of the chest to cover the wound in the mastoid area.The junction of the two pieces of skin was located in the cranioauricular sulcus.Wang Cheng et al[24]reported that the occipital region of the ear was used as the donor site,and the posterior fascia wrapped stent was separated,and the posterior blade thick skin graft was used to cover the cranial ear groove to complete the formation of the cranioauricular angle.Chen[16]and Wang Meishui[17]reported that the scalp blade thick skin graft was obtained by hand,and the good morphology of the cranioauricular angle was obtained,and the donor area did not remain obvious.Scars did not affect hair growth.Zheng Shengwu et al[14]used an electric knife to cut 0.3mm thin and medium-thickness scalp skin grafts.After the follow-up,the hair growth in the donor site was normal,and no scar hyperplasia occurred.

Flap method

After Nagata total ear reconstruction,the skin grafts were contracted by the ear,and the angle of the cranial ear became shallower or even completely disappeared.So,Hu Xiuyun et al[25]designed the posterior sulcus flap to make up for the lack of free skin,in order to maintain the normal position of the posterior sulcus and enhance the stability of the cranioauricular angle.Wang Xi et al[26]reported the design of two opposite triangular arbitrary flaps at the cranioaural sulcus,with the depth reaching to the posterior auricular fascia and pushing each other and then crossorbiting or contraposition suture in the opposite position,free skin grafting on both sides of the flap,postoperative the skin piece was not easy to shrink,and the shape of the cranial ear was stable and reliable.Kang Shensong et al[27]designed a flap in the upper and lower mastoid areas of the reconstructed auricle,respectively,to the cranial groove,suturing the two flaps,covering the supporting cartilage,and the flaps the “two-valve method” of the skin graft of the lateral wound surface raises the angle of the skull.He Mengnan et al[28]picked up the auricle stent,placed the cartilage scaffold into the cranial sulcus,wrapped the fascia behind the ear,and designed two long-shaped upper and lower horn flaps in the mastoid region,which were pulled together close to the cranial ear canal,and the cross and discontinuous suture was performed.The results were satisfactory.Song Xianpu et al[5]designed to use the fascia flap of the pedicle in the tragus,through a tunnel under the ear and below the ear cavity,and fix the fascia flap behind the ear bracket.The ear angle is raised.

DILATED METHOD FOR EAR ELEVATION

Partial expansion method

In 1992,Xia Shuangyin et al[29]reported that the cranioauricular angle was formed by using the first-stage dilator,the second-stage dilated flap to cover the anterior ear,and the posterior ear to cover with fiber capsule combined with free skin grafting.In 2006,zhuang hongxing et al[30]reported the experience of more than 3000 cases of auricle reconstruction:in the first phase,the dilator was implanted;in the second phase,the expanded flap and the posterior ear fascia flap were used to cover the cartilage stent together,and the posterior ear skin graft was added to form the cranial ear horn.

Full expansion method

The full expansion method was first reported by Doctor Hata et al[31]in 1989,Using a 70 ml saline solution to expand the flap.The method in China was first reported by Ai Yufeng[32]in 1993.The expanded flap was completely covered with the cartilage stent,and the cranial ear horn was formed once without the need for supplementary skin grafting behind the ear.The only difference is that an additional incision is needed on the surface of the expanded flap to reconstruct the earlobe.Wang Lu et al[33]proposed that more dilated skin was needed to reconstruct the upper part of auricle to form better auricle and cranial auricle horn.The expansion position was increased to expand the mastoid area behind the ear and the scalp above the ear,and the amount of expanded skin was increased.The hair on the expanded flap could be removed by laser hair removal.Wang et al[34]summarized the experience of using the full expansion method for ear reconstruction in 165 patients with Microtia.According to the size of the auricle of the patient,80 ml or 50 ml of dilator was implanted on the affected side for water injection expansion.The water injection volume is 110 ml or 80 ml.In the secondary ear reconstruction,the flap could completely wrap the ear stent,and cranial ear horn was formed without skin grafting.Gong xiuxian et al[35]reported that in the first stage of operation,50 ml renal dilator was selected to be buried in the subcutaneous layer of the mastoid region behind the residual ear,and the total amount of water injection was about 60 ml.After the completion of water injection,the flap was maintained to expand for 2 weeks.A wedge-shaped base was placed under the ear stent and the expanded skin can completely wrap the auricle stent,without skin grafting.However,this method is recommended for patients with microauricular malformation whose normal lateral ear is small or medium in size and whose cranial ear horn is less than 40 degrees.Li tianyu[36]reported that the reconstruction of the whole ear by embedding 150 ml dilator in the biplane through the residual ear incision could effectively reduce the chest scar area of patients with microauricular deformity,improve the falling range of the dilator,and reduce the incidence of shallow auricular sulcus.Yang Qiao et al[37]reported that the patient was older than 8 years old and had loose skin in the mastoid region of the ear,which favored for the treatment of congenital microtia with “full expansion”auricular reconstruction.According to the size of normal side auricle and the height of cranial ear horn,the water injection amount was usually determined to be 90 ml to 150 ml.The water injection was completed in about 60 days.After the completion of water injection,the expanded flap was maintained for about one month to cover the costal cartilage stent,and the cranial ear horn was formed once.And the effect was satisfactory.

INFLUENTIAL FACTORS OF POOR FORMATION OF CRANIOAURICULAR ANGLE

Poor formation of cranioauricular angle is related to the hyperplasia of scar tissue behind the auricular horn,skin contracture,compression deformation of reconstructed auricle,partial absorption and infection of sculpted auricular cartilage scaffold and other factors[5].Meanwhile,zhang yue et al[38]reported by Logistic multiple stepwise regression analysis that age ≥13 years,hypertrophic scar and non-use of ear protectors were all independent risk factors leading to poor auricular horn formation,as described in the following details.

Age

Costal cartilage will undergo different degrees of calcification deformation with age,which will affect the engraving and biological characteristics of the ear stent.The ear of the 3-year-old child reaches 85% of the adult.After the age of 10,the auricle width stops growing[39].The currently accepted view is that surgery is performed after the age of 6,because the amount of costal cartilage cannot meet the ear reconstruction before the age of 6.Yotsuyanagi et al[40]suggested that asians undergo auricular reconstruction after 11 years of age,not only have sufficient cartilage volume for transplantation,but also the probability of thoracic deformity is relatively reduced.Zhang Yue et al.proposed that age ≥ 13 is one of the independent risk factors for poor formation of the skull angle.In order to maintain the ideal cranioauricular angle and the prognosis of the auricle,8～13 years old was the ideal age for auricle reconstruction.Auricle reconstruction should be carried out as soon as possible,which has certain benefits to patients’ mental and physical health.

Scar Hyperplasia

The cranioauricular angle is usually also affected by the degree of soft tissue coverage.Since the scar can be formed after the surgical incision is healed,the scar hyperplasia pulls or collapses and cooperates with the skin contraction stress,which can destroy the stability of the local area,especially the cranial angle.Zhang Yue et al.found that scar hyperplasia was a high risk factor for poor formation of the skull angle after auricular reconstruction,for patients with obvious tendency of scar hyperplasia after the operation of scar constitution,drug intervention to inhibit scar hyperplasia should be given as needed.

Unused Ear Protectors

Currently,ear protectors commonly used in clinical practice are usually made of low-temperature thermoplastic plates.They are heated and randomly shaped after being attached to the ear structure,and have the functions of ventilation,sound transmission and heat dissipation.Zhang Yue et al.showed that the wearing of ear protectors can effectively protect the expanded flap and the reconstructed ear structure,thereby maintaining the prognosis of the skull angle and the overall appearance of the ear.Hu Zhen et al.[41]believe that the longer the time span of surgery,the greater the risk of potential safety hazards in life leading to tissue expansion or ear reconstruction wear.In addition,some patients were younger,with poor self-protection awareness and compliance,the key and necessity of professional intervention with ear protector is self-evident.

The Thickness of The Flap

The thickness of the flap covering the ear stent and the thickness of the thin flap behind the ear mainly affect the appearance of the substructure of the reconstructed ear.The thickness of expanded flap has a great influence on the appearance of cranioauricular angle.The thin flap is easy to break,which increases the incidence of complications.The thickness of the flap is not conducive to the exposure of the reconstructed ear substructure.Yang Qiao et al[42]proposed a full-expansion of the ear auricle,for patients with thin skin behind the ear,the level of embedded dilator should be deep behind the ear fascia,while the scalp should be under the scalp.In patients with thick skin behind the ear,the implant dilator layer should be located subcutaneously.Liu Jiafeng et al.[43]proposed a method of embedding a dilator in a biplane,the purpose of which was to reduce the distance of the dilator moving down,so that the upper skin was fully expanded,and the effect of reconstructing the upper ear cranial groove was better.Zhang Qun et al[44]used a large-volume dilator to expand the ear in 53 cases,and 2 cases had poor cranioauricular angle.The main reason was the defect of cartilage scaffold sculpture and insufficient relaxation of expanded skin,which formed a tight pull behind the ear,so the skin expansion should be sufficient.

OUTLOOK

Ma Ruhong[45]proposed that the natural substructure construction of auricle is the development direction of auricle reconstruction in the future.Re-creating the auricle not only requires realistic form,but also a strong three-dimensional sense.With the advancement of science and technology and the development of tissue regeneration engineering,how to create a personalized cranioauricular angle with aesthetic and practical functions is bound to become a future development trend.Xu Feng et al[46]in the implementation of the second-stage reconstruction of the second ear cranial angle,combined with the application of three-dimensional modeling technology and rapid prototyping technology can design a personalized cranial angle support,which provided a good condition for obtaining the skull and ear horn with good symmetry and long-lasting stability.Liang Jiulong et al.[8]applied software and 3D printing technology to create the reconstructed auricle and cranial angle model of the affected side,which not only contributed to the fine engraving and assembly of the auricular cartilage scaffold in the second-stage reconstruction,but also predicted the effect of preoperative auricular plastic surgery.Cao Yilin[47]reported the successful construction of human auricular morphological cartilage on the back of nude mice in 1997.The autologous residual chondrocytes combined with PGA/PLA-PCL scaffolds were used to construct auricular morphological cartilage in vitro to reconstruct auricle for patients with small ear disease.After 2.5 years of follow-up,the effectiveness of the method was initially confirmed.Yu Yao et al[48]cultured the discarded residual ear cartilage of patients with microtia in vitro and in vivo and formed normal cartilage-like tissue,but it takes time to achieve clinical application.

SUMMARY

At present,domestic autologous costal cartilage auricle reconstruction is mainly divided into two major mainstreams:Nagata method and expansion method.The auricular reconstruction method suitable for the patient needs to be selected according to the patient’s ear skin condition and cartilage specificity.The Nagata method eliminates the need for a dilator and has a short surgical period to avoid dilator-related complications.At the same time,the Nagata method second stage cranioauricular angle forming post-ear support material can be costal cartilage,which can be artificial material,each has its own advantages,which needs to be determined according to the patient’s own condition;and the fascial flap covering the posterior support material of the ear is bette to select the posterior fascial flap.However,skin grafting is often required,which may cause complications such as contracture or necrosis of the skin,leaving scars in the donor area and having a large difference from the surrounding color.In the case of the expansion method,especially the full expansion method,there is no need to perform steps such as peeling,skin grafting and antiwrap fixation,and the skin scar of the donor site can be reduced and the expanded flap does not have a color difference,and the cranioauricular angle is formed once.However,the operation cycle is long,and medical staff and family members need to be carefully managed during the perioperative period to ensure the success of the reconstructive surgery.In the full-expansion method,the formation of the cranial ear angle also needs to consider the support force of the cartilage support and the flap retraction force covering the ear support.The large retraction force of the flap or the insufficient support of the cartilage scaffold will inevitably lead to poor formation of the cranioauricular angle.How to create a cranioauricular angle with beautiful and practical functions is worthy of continuous exploration and improvement by clinicians.Although rapid prototyping technology and tissue engineering are developing rapidly,it takes time to clinically create a personalized cranial ear angle with aesthetics and function.