Top Articles

One of the most common requests for skull augmentation is for a flat back of the head. In many cases this is for an asymmetric flattening known as plagiocephaly. But in others it is for a symmetric flattening better known as brachycephaly. In the non-synostotic forms of brachycephaly the back of the head lacks projection and the patient has a distinct flattening rather than a more normal convex shape. A custom skull implant is the most ideal method to add increased convexity to the flat back of the head

With the bilateral or more symmetric back of the head flattening comes other dimensional changes that must be recognized in the skull implant design to improve its shape. The cranial height is usually increased to accommodate the lack of intracranial space posteriorly. That can also be some increased posterior temporal width. The normally invisible or minimally detectable occipital knob at the bottom of the occiput may appear prominent.

When designing a skull implant to augment the flat back of the head it is important to first determine the perimeter limits of the implant in side profile. The implant height needs to stop just under the highest point at the crown so no height is added at all. Conversely at the bottom the implant design needs to go as low as possible down to the occipital knob.

The width of the implant design should stay within the maximum width of the posterior temporal region. Anatomically there is thin muscle over the posterior temporal bone so it appears a bit wider than the bone shows. Thus it is important to stay shy of its lateral projection to prevent adding any width from the front view.

With the implant footprint created the location and amount of projection needs to be established. It is usually found by taking the flattest spot on the back of the head and going directly back in a near horizontal direction. How much projection to add depends on how much implant volume is created by doing so. A good guideline is to not exceed 150ccs total implant volume. For most patients this is going to be in the 12 to 14mm range. If one has a prior implant in place or is undergoing a first state scalp expansion much more projection can be done.

With the projection increase centrally comes the need to give it a more convex contour. The central projection can not just taper acutely to the sides. (posterior temporals) That would give it too pointy a shape. Rather the thickness change from central to lateral must have more of an arc shape.

In the non-plagiocephalic flat back of the head a custom skull implant is fundamentally about how to make a symmetric convex shape out of a flat one. Establishing the implant footprint and its internal topography follows several basic dimensional principles.

Dr. Barry Eppley

Indianapolis, Indiana

Top Articles