The disease of congenital hypoplasia and short deformity of bone and soft tissue of one side of the craniomaxillofacial region is called craniofacial shortening or hemifacial shortening in clinical medicine. It is caused by the obstruction of the development of the first and second gill arches in the fetus in the womb. It causes asymmetric deformity of the craniofacial region on both sides. The degree of deformity can be mild or severe.
Clinical manifestations
In severe cases, it also affects the adjacent zygomatic bone, pterygoid pterygoid process, temporal bone, expression muscle, masticatory muscle or subcutaneous tissue, and even orbital heterotopia, microphthalmia and orbital and facial cleft. There may also be associated neurological abnormalities, most commonly facial nerve palsy.
Mandibular deformity: mainly hypoplasia of the mandible, short or completely absent ascending mandibular branch, and upward displacement of the mandibular body, resulting in a deviation of the mandible to the affected side.
【Treatment Method】.
Surgery is required to correct this deformity, and the timing of maxillary and mandibular correction surgery is usually performed after the patient’s jaw development has basically stabilized, i.e. after the age of 16-18 for males and 14-16 for females. The advantages of the mandibular osteotomy and lengthening surgery are: it can be performed early, around 2-4 years old, and can be advanced to about 1 year old for some patients; the surgery is less invasive; the mandible will be physiologically stimulated and tend to grow and develop normally after the surgery; the maxilla will also grow and develop vertically and horizontally under the stimulation of opening and closing or occlusion. The maxilla will also improve vertically and horizontally with open or occlusal stimulation. All these are beneficial to the overall development of the patient’s cranial and maxillofacial body and the restoration of the appearance, as well as to the patient’s psychological health. The basic method is to make an osteotomy in the bone segment to be lengthened, and then place the mandibular retractor, with the adjustment rod leading from the mouth, and start the adjustment to lengthen the mandible one week after surgery, usually 1~2mm per day. the speed and total length of the adjustment is controlled by the plastic surgeon according to the actual situation of the individual. In addition, weaknesses in the soft tissue can be filled by autologous fat tissue grafting. In this way, the jaw and face asymmetry can be improved as a whole. Early correction is beneficial for stimulating the development of the jaw and adjacent bones and for the psychological well-being of the child. Reconstruction of the outer ear can be done as early as 5-6 years of age, when the child’s outer ear is close to adult size. Depending on the individual case and the patient’s wishes, partial or total ear reconstruction can be performed using autologous rib cartilage or biomaterial ear scaffold implants, depending on the severity of the defect. Of course, adult patients who have not undergone ear reconstruction surgery before can have equally good results with this treatment.
Traction osteogenesis technique]
Distraction Osteogenesis is a technique to lengthen the bones by fixing two bone segments with soft tissue attachment and blood supply after amputation, and then gradually distracting them at a certain speed, frequency and direction, during which new bone is formed in the gap between the broken ends.
In 1992, Dr. McCarthy, an American physician, first lengthened the human mandible using retraction osteogenesis, and further reported the clinical experience of a group of 15 patients in 1994. 8 of the 15 patients had unilateral craniofacial shortening, 1 had bilateral craniofacial shortening, and 6 had small jaws due to Treacher-Collins syndrome and Nager Six cases were due to Treacher-Collins syndrome and Nager syndrome caused by small jaw deformity, age 1.6-13.7 years. The mandibular ascending osteotomy was fixed with an external fixator, and the mandible was retracted at a rate of 0.5 mm each time, twice a day, to lengthen the mandible by 18 to 36 mm according to the preoperative design, with an average of 24.5 mm. the retraction was completed and then fixed for 8 weeks. the fixator was removed after X-ray showed bone healing. An appropriately sized occlusal pad was placed in the surgically created posterior space and adjusted by the orthodontist after several months to reduce the volume of the occlusal pad and facilitate the downward growth of the maxillary alveolar process. After the surgery, the occlusal relationship is close to normal and the occlusal plane is close to horizontal at regular follow-up visits. Thereafter, orthodontic treatment is still available.
McCarthy advocates that surgical treatment should be considered when the child is 2 years old and proposes the following indications for mandibular shortening by distraction osteogenesis.
(1) Moderate or severe deformity of the mandible.
②The deformity must be corrected by bone grafting after osteotomy.
(③) Traditional surgical reconstruction through an external incision is required.
We have made technical improvements to the previous method by advancing the start of the corrective surgery; only the bone cortex is cut during osteotomy to protect the periosteum and the inferior alveolar nerve vessels; in general, the intraoral approach is used, leaving no scars on the facial skin.
There are several keys to lengthening the mandible by distraction osteogenesis: preoperative model surgery or surgical simulation is required to determine the cortical incision line, fixation screw position, traction direction and lengthening length. The retraction axis is parallel to the posterior edge of the mandible, the screw position should avoid the tooth root and capsule, and the periosteum, inferior alveolar artery and nerve should be protected during the osteocortical incision. The posterior gap caused by the surgery after bone healing is filled with a dental cementation pad and the thickness is gradually reduced to guide the growth of maxillary and mandibular bone, alveolar bone and teeth.
Technical features]
Retraction of bone formation by a large number of animal experiments and clinical applications, the technology has been perfected, generally divided into four phases.
1, osteotomy: it is best to perform cortical osteotomy, avoid cutting the medullary vessels, and try to protect the periosteum. Some scholars also propose that the blood supply has been re-established one week after complete osteotomy, and only cortical osteotomy is not necessary for bone regeneration, and bone can be formed after osteotomy and retraction as well.
2.Delayed period: the stage from osteotomy to the beginning of distraction, generally 7-14 days, similar to the early stage of fracture repair, to remove the blood clot, clear inflammation, and establish blood supply, when the osteogenic activity has been quite active.
3.drawing open period: the speed of drawing open is very important, too slow to cause premature osteogenesis and fusion, too fast to draw open the gap fibrous tissue formation, resulting in bone disconnection. It is generally believed that the ideal retraction speed is 0.5~1.5 mm per day, which is basically the same as the bone matrix synthesis.
4.Fixation period: the retraction is completed until the retractor is released. During this period, new bone is further formed, matured and modified, and sufficient strength is obtained. This period is not shorter than the retraction period, which is usually 6-8 weeks.
The improved technique avoids many complications, such as infection, necrosis, and bone disjunction. With bone grafting after osteotomy, the recurrence rate is as high as 40% to 64%, while retraction of distraction osteogenesis is rare and retraction is about 7%. Small intraoral retraction fixators are used to avoid skin scars; cautious operation is used to avoid damage to the dental capsule.
In conclusion, retraction osteogenesis is simple and safe, with stable and reliable results, no bone grafting, little damage, easy to control, the family learns to adjust the retractor soon after surgery, short hospital stay, no intermaxillary ligature fixation, and provides a new method for the correction of short hemifacial mandibular hypoplasia and underdevelopment of the midface. In recent years, medical device companies in the United States and Germany have produced three-dimensional retractors and intraoral retractors, and their use has reduced the occurrence of complications. With the advancement of craniofacial plastic surgery technology, traction lengthening osteogenesis has been extended to the correction treatment of midface and cranial deformities.
Typical cases
1, congenital hemifacial short deformity, after traction lengthening osteogenesis, facial appearance improved, occlusal plane restored, good masticatory function.
2.Temporomandibular joint ankylosis, chin retraction ornithosis, small jaw deviation complex deformity, after arthroplasty and traction osteogenesis, the facial appearance was normalized and the open mouth motor function was restored.