Background: The most successful forms of significant aesthetic skull augmentation involves the placement of a custom designed implant directly on the skull bone under all layers of the scalp. The most commonly used custom skull implant is made of solid silicone for both ease of placement through a much smaller scalp incision and lower manufacturing cost.
But solid silicone is not the only custom-designed skull augmentation material that is available. The first custom-design skull implant used in skull surgery was HTR (Hard Tissue Replacement) which is a porous material composed of PMMA beads coated with pHEMA. (Which gives it a hydrophilic property) It has a long track history as a skull bone flap replacement for inlay bone defects in which it has demonstrated extensive fibrovascular tissue ingrowth and even some bony ingrowth.
But it has rarely been used as an aesthetic onlay material as it rigidity mandates a wide open scalp exposure and it can not be manufactured with feather edges. But if one can accept a full open coronal scalp incision (or already has the scar from a pre-existing one) and one is prepared to be able to smooth the implant edges circumferentially, then the HTR material offers a good implantation material.
Case Study: This male had a prior history of a failed back of the head skull augmentation procedure using bone cement. It become infected and was removed. A large zigzag coronal scalp incision was used for its placement. A custom HTR skull implant was designed of 20mms projection and the blunt edges were feathered using bone cement.
He went on to heal uneventfully and was not seen again for ten years when he returned for a custom forehead implant. His 3D CT scan showed the implant is good position as would be expected with a normal underlying skull bone surface.
His ten year result shows a significant improvement in the shape/projection of the back of his head with a well healed scalp incision.
The back of the head has always been one of the top desired locations for augmentation. In certain ethnicities this desire is common given the natural development of the skull to have less front to back projection. Numerous implant materials can be used which can be successful but the incisional needed to place them can influence that decision. Biologically HTR is a great material due to true complete fibrovascular ingrowth but its stiffness and lack of feather edges make its use aesthetically challenging. Its long term success is no surprise given these favorable tissue properties
Key Points:
1) Effective back of the head augmentation can be done with 20mm of implant projection…if the scalp can accommodate it .
2) While few patients ever want a full coronal scalp incision for an aesthetic skull augmentation it does allow for the placement of a rigid skull implant material like HTR.
3) A ten year 3D CT scan followup shows no evidence of any adverse reaction of the skull bone to the implant.
Dr. Barry Eppley
World-Renowned Plastic Surgeon