Cranial defects are mostly caused by open cranial injury or firearm penetrating injury, and some patients have residual bone defects due to surgical decompression or resection of diseased cranium. Defects of more than 3 cm in diameter, especially those located in the frontal area, are often characterized by one or another symptoms, such as dizziness, headache, local tenderness, irritability, restlessness, etc.; or the patient is afraid of the pulsation, expansion, collapse of the defect area, fear of sunlight, fear of vibration and even fear of loud noises, often with poor self-control, concentration and memory loss. Etiology: 1, open craniocerebral injury, especially after the firearm injury for debridement, the skull itself that there is a fracture fragmentation, the wound is a bacterial open wound, easy infection fracture can not be reset. 2, closed craniocerebral injury to remove the hematoma, contusion of inactivated brain tissue after the intracranial pressure is still high and decompression of the bone flap. 3.Osteoma and other cranial bone lesions after resection. Cranial bone is membranous bone regeneration capacity is poor, new bone mainly from the inner periosteum, and after 5 to 6 years old that is lost bone regeneration capacity. Those with a diameter of less than 1 cm can heal bony and those with a diameter of 2-3 cm or more are difficult to repair, thus leaving a cranial defect. Clinical manifestations Usually, skull defects less than 3cm are asymptomatic; after performing temporal muscle decompression or suboccipital decompression, there are hypertrophic muscles and fascia covering and forming a tough fibrous healing layer in the defect area, which can play the role of the original skull to protect the brain, and there is no symptom in the clinic. Clinical manifestations of cranial defects: defects with a diameter of more than 3 cm, especially those located in the frontal area, which hinder the beauty and safety, often have one or another symptoms, such as dizziness, headache, local tenderness, irritability, restlessness, etc.; or patients have fear of pulsation, expansion, collapse of the defect area, fear of sunlight, fear of vibration and even fear of noisy sound, often have poor self-control, difficulty in concentration and memory The patient’s head is severely deformed due to large skull loss, which directly affects the physiological balance of intracranial pressure, collapsing when standing upright, expanding when lying down, concave in the morning and convex at night; or the atmospheric pressure acts directly on the brain tissue through the defect area, which inevitably leads to local brain atrophy and aggravates the symptoms of brain wasting over time, and at the same time, the affected ventricles gradually expand or deform to the defect area. At the same time, the affected ventricle gradually expands or deforms into the defect area. In addition, the cranial defect of children can become larger with the development of brain tissue, the edge of the defect will turn outward, and the protruding brain tissue will gradually show progressive atrophy and cystic change, so children need a complete cranium to ensure the normal development of the brain. Repair materials Titanium mesh for cranial defect repair The repair materials available for cranioplasty are autologous tissues and allogeneic materials, the former using the patient’s own ribs, iliac bone or cranial bone, and the latter being polymer and metal implant materials. The former is made of the patient’s own ribs, iliac bone or cranial bone, while the latter is made of polymer and metal implants. At present, the latter method is being used more and more. The timing of skull defect repair should depend on the patient’s general and local conditions, such as after the removal of collapsed bone fragments for simple depressed fractures, the repair can be completed in one operation at the same time. However, for cranial defects caused by open craniosynostosis, cranioplasty should be considered after the initial debridement and wound healing for 3 to 6 months. If the open wound is already infected, repair surgery should be postponed until the wound has healed for at least six months. Traditional non-degradable bioprosthesis can only be used as a filling material for skull defects. With the development of medical and tissue engineering technologies, various synthetic biomaterials have emerged, but these materials cannot be absorbed by the body after transplantation, have rejection and inflammatory reactions, and are difficult to integrate with the host bone. Currently, domestic cranial bone repair materials Plexiglas, silicone rubber, titanium plate, titanium mesh and other organic materials are used. These materials have disadvantages such as easy aging, easy breakage, not easy to shape or poor biocompatibility, etc. Among them, titanium mesh and titanium plate are easy to conduct heat and electricity, causing patients to have head burning sensation in high temperature environment after surgery, and the price of titanium mesh plate is expensive. For silicone rubber materials, although the biocompatibility is better, but there is a problem of low strength. The ideal bone graft material should have good biocompatibility and integration ability, chemically stable, maintain its shape for a long time after surgery, not easy to slip off and displace, predictable long-term biological properties, easy to shape, easy to contour, and cheap. Metal skull forming sheet such as stainless steel plate and mesh, tantalum plate or titanium alloy plate and mesh have strong anti-pressure performance and good tissue compatibility, but because of the thermal conductivity, sharp edges are easy to penetrate the scalp and have the disadvantage of affecting the X-ray examination, which is yet to be improved; flat plexiglass is heated and shaped as repair material, which has the advantage of convenience and ease of use, but the effect is poor for orbital and nasal root, which have high plastic requirements, and At the same time, it is not the ideal material because of its poor punching strength and easy to break. The plastic self-consolidating material made of polymeric materials methyl methacrylate and styrene copolymer powder plus methyl methacrylate monomer aqueous mixed with each other, has good plasticizing properties, and can be self-cured to form a strong and stable permanent implant, with the advantages of suitable strength, good tissue compatibility, not easy to degrade, and does not affect the X-ray examination. In recent years, some people have added pore-making agents to the above two-component materials to develop plastic microporous artificial skull materials. After implantation, fibroblasts can grow into the microporous implant, which makes the implant fuse with the tissue and has the tendency of calcification and ossification, so it can be considered as a more ideal material for cranial repair. In addition, new cranial implants made of mesh-reinforced silicone rubber cranial plate, hydroxyapatite or ceramic materials also have good performance in cranial defect repair. The currently accepted indications for surgery are: 1, skull defect larger than 3cm in diameter. 2. The defect is aesthetically displeasing. 3.It causes long-term dizziness, headache and other symptoms that are difficult to relieve. 4. Meningeal-brain scar formation with epilepsy (simultaneous epilepsy focal resection is required). 5.Severe mental burden affecting work and life. For patients with incomplete initial debridement, local infection, intracranial lesions and increased intracranial pressure, skullplasty should not be performed for the time being. In addition, some patients with poor general condition, serious neurological deficiency and unable to take care of themselves, or those with thin scalp and large scar in the deficient area should not be repaired hastily, and can be temporarily protected with a local helmet, and then consider the surgery after the conditions are mature. There are many kinds of materials for skull repair, each with its own advantages and disadvantages. Although autologous bone has little tissue reaction, it needs to be operated in both the bone donor area and bone graft area, which increases the patient’s pain and has poor plastic surgery results. Some people bury the bone fragments removed by decompression of the large bone flap under the abdomen as a future repair, because two surgeries are required, and the bone fragments are often absorbed and become smaller so that they become loose and concave, and allogeneic bone is used because it is refrigerated in the bone bank, increasing the chance of contamination, and foreign body reactions are also greater, so they are rarely used. In the past, it was recommended to perform cranial repair 3 months after decompression of the bone flap, but nowadays, it is advocated that the earlier the repair, the better the recovery of cerebral nerve function. Surgical method Under local or general anesthesia, the scalp incision is curved, and the blood supply to the basal part of the flap is fully ensured. When separating the scalp, do not damage the deep dura mater to avoid postoperative fluid accumulation. When using the overlay method of repair, the periphery of the bone defect area does not need to be trimmed and the bone coat does not need to be cut, and the defect area can be covered with an implant slightly larger than the defect, and the surrounding area can be fixed to the bone coat with thick silk. However, it is necessary to use strong, good quality and thin surrounding material to match the shape and curvature of the skull. If the inlay method is used, the bone coat should be cut and trimmed along the edge of the bone defect, and then the appropriately cut implant should be inlaid on the bone defect, and the surrounding holes should be fixed on the bone edge with thick wire. Care should be taken not to open the frontal sinus when performing inlay repair in the forehead to avoid infection. After the operation, the scalp should be sutured in layers and dressed with appropriate pressure.