Custom skull implants provide a contemporary method of aesthetic skull augmentation for a wide variety of head shape deficiencies. While the most common material for such custom skull implant is solid silicone, no skull augmentation material composition will allow tissue ingrowth. Tissue ingrowth should not be confused with tissue adhesion. Tissue ingrowth is where an actual through and though tissue ingrowth occurs where the underside of the scalp reconnects with the skull bone with a direct fibrovascular connection.
In solid implants the only way to create tissue ingrowth is with a modification of the material. The technique that I used is to place full thickness holes through the implant using a dermal punch. (which is commonly used for taking skin biopsies. It is a circular blade and handle that comes in a variety of widths from 1mm to 6mms in width. It cuts easily through solid silicone and I typically used punches from 4 to 6mms depending on the size and thickness of the implant. How many perfusion holes to place is variable but more is better than less.
There is no question that extensive fibrovascular tissue ingrowth occurs through these holes as has been repeatedly seen whenever a skull implant is revised/replaced/removed. The soft tissue pillars of soft tissue are quite adherent and will bleed when cut/released. Such tissue ingrowth reliably occurs in any primary skull implant placement. It less reliably occurs when there is an established capsule from prior skull implants which are replaced for shape/size concerns. This would be expected as the surrounding tissue response in an existing implant site is far less robust than occurs later.
While such tissue ingrowth occurs through the perfusion holes of a skull implant, what is their biologic purpose? First it provides multiple points of implant fixation. Rather than having an implant in a single large encapsulated space, the multiple points of tissue ingrowth are like individual ‘nails’ holding it into place. Secondly re-establishing intramaterial soft tissue connections reduces the potential risk of seroma fluid collections during healing. (e.g., they play the same role that quilting sutures do in a tummy tuck) Lastly, any tissue connections that allow blood vessels to take a shortcut through the implant rather than around it is a favorable biologic event.
Dr. Barry Eppley