Cosmetic skull deformities encompass a wide variety of concerns from flatness, pointy or high spots, ridges, bulges and asymmetries. But one of the most common head shape concerns is the flat back of the head. This specifically refers to varying degrees of lack of occipital projection, usually occupying an area between the top of the skull in the back down to the horizontal level of the upper portion of the ear. The causes are well known as a minor variant of occipital brachycephaly and often develop from early infantile positioning.
While flatness of the back of the head may seem trivial, to some affected it represents a significant aesthetic concern. The lack of a round posterior cranial shape is hidden by those concerned with caps and hairstyles and even devices that make the hair have more projection. Some refuse to go swimming so their hair is not flattened to reveal an absent occipital roundness. Others feel their ‘flat head’ make them look unattractive and facially disproportionate.
The flat back of the head can undergo aesthetic improvement by a skull reshaping procedure known as an augmentation cranioplasty. Using either a plastic or hydroxyapatite material, an improved occipital shape can be obtained by building up the bony contour. Either material is applied in a putty-like state and manually shaped to the desired form until firmly set. Depending upon the incisional access and the amount of surgical exposure, the amount of cranial expansion can be up to 15mms to 20mms of augmentation if a competent scalp closure can be obtained.
A unique feature of most augmentation onlay cranioplasties, regardless of their location, is that the material must be applied to a smooth round surface. In addition, these round skull surfaces offer no inherent stability with most of their locations being the equivalent of on the ‘side of a cliff’. As no known onlay cranioplasty material truly integrates into the underlying bone (or bone grows up into the implanted material), engagement of the material onto the skull’ surface has benefit. This is most conveniently done with small screw fixation.
Screw fixation of onlay cranioplasties, however, is not done as one envisions it for other facial implants. The implanted material is not first applied and then secured into position by screws. This is how it is done for preformed implants. Onlay cranioplasties are formed after they applied. Thus screws are initially placed and serve as a means of anchoring or something for the material to grab onto once applied, like metal rebar in concrete. This is particularly useful in occipital cranioplasties in which the material must be applied on the vertically-oriented back of the head where slippage and material displacement is very likely.
The pre-material placement of screws in onlay cranioplasty is useful for more than just implant anchorage. They are also helpful in setting the thickness of the applied material. By placing screw with lengths for the amount of thickness desired, the material can be applied using the screws as contouring guides.
Occipital cranioplasty can provide significant cosmetic improvement to those afflicted with a flat back of the head. Modern biomaterials such as titanium screws and acrylic and hydroxyapatite composites can very effectively create a more aesthetically pleasing occipital contour. Soon custom skull implants made from the patient’s 3D CT scan may become the preferred skull augmentation method.
Dr. Barry Eppley
Indianapolis, Indiana