What is hemifacial shortening? Hemifacial shortening, which was introduced by Gorlin and Pindborg in 1964, is also known as hemifacial shortening, hemifacial shortening, first and second cheek arch syndrome, auriculo-mandibular dysplasia, mandibular-facial dysplasia, unilateral facial dysplasia, etc. It is the most common congenital craniofacial malformation after cleft lip and palate malformation, mainly related to the obstructed development of the first and second cheek arches in the fetus in utero. It is the most common congenital craniofacial anomaly after cleft lip and palate. The deformities that exist after birth worsen with growth and development. The lesions are mostly unilateral, with some bilateral involvement, and involve dysplasia of the craniofacial skeleton, muscles, soft tissues, facial nerve, and external ear. Because the deformities can involve multiple anatomical sites and vary in severity, a comprehensive treatment plan must be developed depending on the severity of the deformity. Clinical manifestations of hemifacial shortening: In the clinical manifestations of hemifacial shortening, multiple anatomical areas can be involved and the severity varies, manifesting as shortening of the affected face, weak subcutaneous soft tissues, chin deviation, facial nerve hypoplasia, transverse facial cleft and external ear deformity. Due to the asymmetrical development of the mandible, the chin is mostly deviated to the affected side and the occlusal plane on the affected side is shifted upward. Other craniofacial skeletal involvement is related to the severity of the mandible. The maxilla and zygoma on the affected side are dysplastic, and the zygomatic arch is narrow or even absent. Some patients have microphthalmia. The frontal bone on the affected side may show flatness, similar to the manifestation of oblique head deformity. The masticatory muscles on the affected side are dysplastic, including the occlusal, internal pterygoid, external pterygoid and temporal muscles, and the function of the muscles is correspondingly impaired. The external ear is almost always deformed to varying degrees, with the milder cases having preauricular dermatomes, sinus tracts, and varying degrees of abnormalities in the shape, size, and position of the external ear, or even complete absence and atresia of the external ear canal in the more severe cases. The skin and subcutaneous tissues of the cheek can be dysplastic, and the parotid gland can be hypoplastic or absent. Treatment options: Previous surgical options include bone grafting, maxillary LeFort type I or III osteotomy, and mandibular sagittal split osteotomy. If necessary, autologous rib cartilage or ribs are used to reconstruct the condyle and ascending branches of the mandible. In the absence of zygomatic arch, the zygomatic arch is reconstructed with autologous rib bone. In cases with hypoplasia of the infraorbital and lateral margins, a unilateral maxillary LeFort III osteotomy should be performed to move the orbital margin forward, and a LeFort I osteotomy should be performed on the opposite side to correct the inclination of the occlusal plane. For patients with one side involving craniofacial bone dysplasia, surgery should be performed in stages, with the entire orbital bone being pushed forward and upward in a combined intracranial and extracranial route in the first stage, and in the second stage via the mouth after 6 months. The chin deviation can be corrected by horizontal osteotomy of the chin. In addition, fat injection and dermal fat grafting or microsurgery can be used to further correct the facial asymmetry if necessary. The main option currently used is to apply mandibular lengthening for hemifacial shortening, and if there is an ear deformity, ear deformity correction or even ear reconstruction can be performed at the same time. The specific steps of mandibular lengthening are: 1. Pre-operative design according to the CT film of the mandible, i.e. selecting the suitable osteotomy line position and lengthening direction as well as the size of the lengthener according to the severity of the mandibular ascending branch and body deformity, and preparing the surgical guide plate. Of course, the computer can also be used to show the simulation of the operation and predict the postoperative effect; 2. intraoperative placement of the lengthener; 3. postoperative gradual lengthening of the mandible in both vertical and horizontal directions by means of the lengthener, with the chin rotated and reset to the healthy side. The lengthening is accompanied by the lengthening of blood vessels, nerves, skin, muscles and other soft tissues, which improves the postoperative stability.4. The lengthening device is removed in a second operation about one year after surgery. Although the patient’s short hemifacial deformity can be greatly improved by mandibular lengthening, it still needs to be combined with some of the other procedures mentioned above to achieve a more satisfactory result. Other facial contouring procedures based on mandibular lengthening will, of course, be significantly less invasive in terms of scale and intraoperative trauma. Timing of treatment: Most studies have shown that hemifacial shortening increases with growth and development, which is related to the timing of treatment. Early treatment of the deformed mandible can prevent and reduce the formation and extent of secondary deformities and promote the coordinated development of the craniofacial skeleton. Moreover, if the mandibular deformity can be corrected before school age, so that the period is in the period of tooth replacement, the occlusal relationship can be better improved through self-adjustment when permanent teeth erupt. However, it is not easy to use mandibular lengthening treatment too early, because too small and weak mandibles are not conducive to the placement of lengthening devices, and if ear reconstruction is performed at the same time, the smaller rib cartilage is not conducive to the shaping of the ear brace during surgery.