Background: Of the five surfaces of the skull aesthetic deformities of the back of the head are the most commonly treated. One of the typical concerns is when the back of the head is flat whether it is on one side or involving the entire back of the head. When it is the entire back of the head it is a profile issue that reflects a lack of an adequate cranial curvature. By anthropometric standards the Golden Ratio of the skull is adversely affected with the bregma-inion line being short and abnormally shaped compared to the bregma-nasion line.
In designing a custom skull implant for the flat back of the head how to properly establish its projection to normalcy is not an established science. The number of surgeons who have ever done custom skull implants for onlay augmentation is so few that doing so is more of an art than a science. But there is a method to it and it begins with establishing the point of maximum projection which is initially placed at the center of the area of flatness. The height of this projection establishes a midpoint of the arc or new shape of the back of the head.
Case Study: This male was long bothered by the flat back of his head and didn’t know until more recently that there was an aesthetic solution for it. His 3D CT scan showed a flat profile shape to the back of his head from the lambdoid suture up to the posterior sagittal area.
A custom skull implant was designed that had 12mms of projection and 100ccs of volume. As is often the case in back of the head implants that improve the overall shape it was wider than it was tall.
Under general anesthesia and in the prone position a wavy 7cm long incision was made on the back of the head over the nuchal ridge. Through this incision the custom skull implant was placed aided by the internal wedges designed on the inside of the implant. Two small titanium microscrews were placed to secure its position.
The immediate change in the shape of the back of his head could be seen at the end of the surgery.
Pre-designed custom implants are the most effective method for any form of skull augmentation, particularly the flat back of the head. By having a predetermined shape a predictable postoperative shape change is assured that is smooth and symmetric. The one challenge with a preformed implant is getting it through a small incision. Unlike breast implants which are composed a viscous silicone gel that is extremely deformable and can undergo great shape deformation to pass through a small skin incision, custom skull implants are made from a much stiffer solid silicone with such less shape deformation capability. As a result improving the implant’s deformability has to be made into its design., (internal wedges)
1) The flat back of the head often has an anterior angulation in profile from the nuchal ridge or lambdoidal suture line superiorly.
2) Re-establishing a normal curve to the skull in profile (inion – bregma curve) is one important design feature of making custom skull implant for the flat back of the head.
3) The custom back of the head implant is usually placed through a low small horizontal scalp incision which is way smaller than the diameter of the implant.
Dr. Barry Eppley