In many cases, there are many patients with cranial defects caused by trauma, brain surgery, etc. Cranial defects seriously affect the appearance and quality of life of patients, so timely repair of cranial defects is essential. The following is a brief introduction about the timing, indications, contraindications, repair materials and repair methods of cranial repair. I. Necessity of cranial repair In cranial defect, due to the loss of protection of bone flap, the effect of atmospheric pressure will disrupt the ipsilateral cerebrospinal fluid circulation and decrease cerebral blood flow, leading to potential brain tissue damage. Large skull defects can easily cause deformation and displacement of brain tissue, enlargement of the ventricles, and disturbance of water flow in the brain parenchyma, which affects the production, absorption and circulation of cerebrospinal fluid, resulting in complications such as traumatic hydrocephalus and cerebral bulge. This causes a series of neurological symptoms such as headache, dizziness, local tenderness, irritability, anxiety, fear, unexplained discomfort and various mental disorders in patients, called trephined syndrome. After cranial repair, the flow of cerebrospinal fluid is significantly improved and cerebral blood flow is somewhat increased. The brain injury is improved. The timing of repair is usually considered that cranial repair should be performed more than 3-6 months after debridement and decompression, and for those with infection, it should be extended to at least 6 months after debridement and decompression. If the time is too long, the local skin scar will be firm and not easy to heal after surgery, and the skin and meninges or brain tissue will be closely adhered, which increases the difficulty of separation in surgical operation and the damage to the skin? and brain tissues are more damaged. The skin flap collapse time is too long, easy to cause flap shrinkage, and the tension of the skin edge after suture is easy to cause ischemic necrosis. Third, repair materials Nowadays, the most used artificial materials in major hospitals are titanium mesh plates, which are more and more widely used clinically because of the non-toxic, low inflammatory and allergenic, convenient plasticity, good biocompatibility and low biomorphism, and high corrosion resistance of titanium alloy materials. After implantation, fibroblasts can grow into the micro-pores of the titanium mesh, which makes the titanium mesh fuse with the tissue and has the tendency of calcification and ossification, making it a more ideal artificial repair material. Some people believe that autologous cranial bone is the most ideal material for repairing cranial defects. However, there are practical difficulties in how to preserve and not contaminate it. Traditional cranial repair materials with plexiglass, methyl methacrylate bone cement, titanium plate, silicone rubber plate, etc. have also been gradually reduced. Fourth, autologous cranial bone preservation Autologous bone flap preservation, mainly autologous preservation and liquid nitrogen cryopreservation, in recent years, there are also reports about deep cryopreservation of autologous cranial bone, the cranial bone flap after deep cryopreservation maintains the activity of bone tissue cells, has the same osteoconductive effect after preservation using other methods, the bone guide in the frozen bone flap matrix is not inactivated, and still maintains the osteoinductive ability, which can be promoted after transplantation The bone guides in the frozen bone flap matrix are not inactivated and still maintain osteoinductive capacity, which can promote the fusion of the grafted bone with the recipient bone after transplantation. However, deep cryopreservation of cranial bone flap must have certain equipment conditions and high cost, and most hospitals do not carry out it. V. Repair method In recent years, 3D printed cranial titanium mesh is widely used to repair cranial defects. With the application of computer and 3D image reconstruction technology and the use of automatic molds to make titanium plates, the shaping is more perfect and precise. VI. Indications for surgery The currently accepted domestic standard is cranial defect diameter > 3 cm, especially the defect of important functional area, which is easy to cause neurological dysfunction. Early cranial repair is possible: 1, the patient is in good general condition, clear consciousness, no pulmonary infection; 2, no intracranial hypertension, collapse of skin flap in the cranial defect area; 3, no intracranial and skin infection foci in the operation area; 4, no obvious edema of brain tissue in the operation area, no obvious displacement of midline, no hydrocephalus on cranial CT examination; 5, cranial defect >3 cm or more. Both the defect site and defect area should be considered, and the physical condition of the patient should be taken into account. Cranial repair is not recommended in the following cases: local scalp infection, intracranial foci of infection resulting in increased intracranial pressure, thin scalp in the defect area, poor general condition, severe neurological deficit, and those who cannot take care of themselves. For patients with early intracranial infection, early repair is not recommended. For small defects (<3 cm) that do not affect function and aesthetics, repair is not necessary. Especially for patients with long-term coma, vegetative survival, brain death, and postoperative malignant tumor, do not repair blindly. The contraindications of cranial repair should be: high intracranial pressure, intracranial occupancy, brain swelling, and abnormal cerebrospinal fluid. The more common complications after cranial defect repair are subcutaneous fluid, bleeding, infection, bone flap loosening and sinking, titanium nail loosening, plexiglass breaking, material exposure, etc. In recent years, the development of bone tissue engineering has provided a new method for the complete repair of cranial defects, which mainly involves the application of extracellular matrix compound expansion of cultured seed cells, implanted back into the defect site, and while the extracellular matrix is gradually degraded, the implanted cells keep proliferating to achieve the purpose of repairing cranial defects. It is currently in the research stage and is expected to be used in clinical practice in the future.