Cranioplasty

Surgical operation on skull

Cranioplasty is a surgical operation on the repairing of cranial defects caused by previous injuries or operations, such as decompressive craniectomy. It is performed by filling the defective area with a range of materials, usually a bone piece from the patient or a synthetic material. Cranioplasty is carried out by incision and reflection of the scalp after applying anaesthetics and antibiotics to the patient. The temporalis muscle is reflected, and all surrounding soft tissues are removed, thus completely exposing the cranial defect. The cranioplasty flap is placed and secured on the cranial defect. The wound is then sealed. Cranioplasty was closely related to trephination and the earliest operation is dated to 3000 BC. Currently, the procedure is performed for both cosmetic and functional purposes. Cranioplasty can restore the normal shape of the skull and prevent other complications caused by a sunken scalp, such as the "syndrome of the trephined". Cranioplasty is a risky operation, with potential risks such as bacterial infection and bone flap resorption.

The word cranioplasty can be broken down into two parts: cranio and plasty. Cranio originates from the Ancient Greek word κρανίον, meaning "cranium", while plasty comes from the Ancient Greek word πλαστός, meaning "moulded" or "fashioned".

The operation has its cosmetic value as the normal shape of the cranium of patients is restored instead of the presence of a sunken skin flap, which may affect the confidence of patients. It also has its therapeutic value as the operation provides structure to the skull and protection to the brain from physical damage. The timing of cranioplasty is affected by multiple factors. Sufficient time is required for the recovery of the incision from the previous operation, as well as to clear any infections (both systemic and cranial). as well as an increased incidence of hydrocephalus. The use of autograft is also associated with a high rate of bone resorption. on the other hand, materials such as methyl methacrylate and autologous bone is associated with a higher infection rate. Other risk factors for infection include previous infections, contact between sinuses and operation site, devascularized scalp (loss of blood supply in the scalp), previous operations, and type of injury. Sanan and Haines stated that the materials being used for cranioplasty were associated with the status of the patient. The first true description of cranioplasty in Europe was made by Fallopius in the 16th century, stating that the fractured cranium should be removed and be reinserted with a gold plate if the dura was damaged. This was questioned by other practitioners at his time, concerning that surgeons may keep the gold instead of using it for surgery. The first cranioplasty was reported by the Dutch surgeon Job Janszoon van Meekeren. The report described the use of a segment of a canine cranium as a material for cranioplasty on a nobleman in Moscow. The operation was successful, however, the use of canine bone in the operation was not accepted by the church and the man was forced to leave Russia. Autografts, allografts and synthetic materials are the main types of materials used for cranioplasty. Autografts, or autologous grafts, are body tissues taken from the patient. The first successful cranioplasty using an autograft was recorded in 1821, with the bone piece being reinserted into the cranium. The operation achieved partial healing. Subsequently, more studies and operations were carried out with autografts. A successful case of reimplantation of cranial bone was reported by Sir William Macewen in 1885, popularising autografts to be material for cranioplasty. Succeeding operations involved autografts taken from different parts of the patient's body, such as the tibia (leg bone), scapula (shoulder blade), ilium (hip bone), sternum (chest bone), along with fat tissues and fascia. when there is a high demand for cranioplasty due to a large number of injuries. It becomes malleable when an exothermic reaction occurs between its powder form and benzoyl peroxide, allowing it to be moulded to the cranial defect. Titanium is non ferromagnetic and non corrosive, making the host free from inflammatory reactions. It is also robust, thus preventing patients from trauma. The use of titanium is associated with a lower infection rate. Disadvantages of using titanium include its high cost, poor malleability, and disruption to CT scan images. Hydroxyapatite is a compound of calcium phosphate being arranged in a hexagonal structure. It bonds well chemically with bones and inflicts little inflammatory reaction by the host, and has good osteointegration. It can be expanded and is used in paediatric cranioplasty. It can be moulded smoothly and has appealing cosmetic results. However, the material is brittle and has low tensile strength, and is only suitable to be used for small cranial defects. Its use is also associated with a high infection rate. Hydroxyapatite is often used with a titanium mesh to prevent fractures and for better osteointegration.