MedStar Georgetown's Cranioplasty Team: Overview of Techniques
Bone Cement Cranioplasty
Hydroxyapatite, or bone cement, is the material used during this procedure. Hydroxyapatite is identical to the crystalline structure of bone; however, it does not contain any of the proteins associated with living bone. This bone cement is similar to surgical spackle, and it is used to smooth irregularities and fill creases to smooth the bony contour. For minor to moderate irregularities of the head, hydroxyapatite bone cement is an excellent material to smooth the surface and re-create a normal contour and shape for the patient.
Autologous cranioplasty refers to using the patient's own bone to restore the normal shape of the head. Bone used to restore the shape can either be taken from the original skull itself, the ribs, or the hip. The advantage of using the patient's own bone is that it will incorporate into adjacent bone and develop its own blood supply. The fact that the bone develops its own blood supply makes it more resistant to infection over time. A cranioplasty made from the patient's own bone can frequently be treated with less invasive measures in the long-term. When possible, autologous reconstruction is most beneficial in comparison to that of an implant.
An implant is usually indicated in a repair that requires a large amount of skull bone to be replaced. These implants are fabricated from a CT scan of the patient's head. It is important to have a team of specialists when designing the implant because the implant design may be modified based on surrounding tissue. For example, the implant may be thinned or modified based on surgical access during the procedure. Our team of surgeons allows for the opportunity to discuss and address any aspects of the reconstruction that may require a modification with the implant design. The three materials that are listed below are usually used to create the implant.
- PEEK (polyether ether ketone) This material is the newest version of the available cranioplasty materials. It has a high strength to weight ratio and can be created in the multitude of three-dimensional configurations. Its use was popularized at Walter Reed Hospital during the Iraq and Afghanistan conflicts. It has a safe to use track record and is the most common material used in large cranioplasty defects at our institute.
- PMMA (polymethylmethacrylate) Methylmethacrylate is the oldest material that is currently used to make implants. It is less likely to be used for a permanent implant; however, it is very useful in making temporary implants in cranioplasty. Antibiotics can be mixed into the methylmethacrylate making it a useful temporizing device to maintain a clean sterile field while awaiting a more permanent implant.
- Medpore (polyethylene) Polyethylene implants are also popular. They tend to be lightweight and are easily contoured during the operation for difficult situations. These implants are popular and are used almost as much as the PEEK implants.
Microvascular surgery is a subspecialty of plastic surgery and allows the surgeon to bring healthy tissue into a compromised scalp wound. Both severe infection and a previous history of radiation can lead to tissue that is difficult to heal. The technique of microvascular surgery allows the surgeon to bring healthy tissue from a different part of the body along with its artery and vein. This tissue can then be placed into the wound on the head, and the artery and vein supplying the tissue can be reconnected to an artery and vein near the head wound. This is a valuable tool in treating complex wounds of the head that would otherwise be untreatable.
Tissue expansion is a technique that allows the surgeon to grow healthy tissue. A tissue expander is similar to an empty water balloon that is placed under the skin and that is gradually expanded using sterile water. As the expander enlarges the skin over the top of it stretches creating normal healthy skin that can then be used to cover an area of exposed bone or damaged tissue. This technique has been used in plastic surgery for many decades with an excellent record safe and successful outcomes.
Virtual Surgical Planning
Virtual surgical planning is the technique that couples the surgeon with a biomedical engineer. The patient's CT scan allows both the surgeon and the biomedical engineer to see the areas that need to be corrected with the implant. By designing the implant together, both the surgeon in the engineer create a precise implant that will restore the patient to normal form while also providing the protective function of normal bone. The precision of computer treatment planning allows an implant to be restored to ideal anatomic form.
Autologous Fat Grafting
Autologous fat Grafting is an established technique in plastic surgery where the surgeon harvests fat and processes it in a special way to retain the viability of the fat cells. The fat can then be injected through special cannulas to create normal form. This technique is extremely useful and creating soft tissue volume in both reconstructive and aesthetic surgery. The surgeons in our cranioplasty team use this technique to add volume in the temporal regions as well as other areas where both volume and texture of soft tissue need to be enhanced. This is a minimally invasive technique and can be done easily on an outpatient basis.
Postoperative sequela or common deformity after neurosurgical procedures is temporal hollowing. This occurs when the temporalis muscle is altered during the surgical approach by the neurosurgeon and subsequent atrophy or shrinking occurs. The plastic surgeons in the cranioplasty team have extensive experience in techniques correcting temporal hollowing. Our surgeons can identify, isolate, and resuspend the temporalis muscle. This technique is frequently augmented with either dermal fat grafting or autologous fat grafting to restore normal form.
Dermal Fat Grafting
Dermal fat grafting is an older technique within plastic surgery that benefits during cranioplasty reconstruction. Dermal fat grafting refers to taking a portion of the skin and its associated fat to create a durable volume augmentation tool. This is used successfully in the treatment of temporal hollowing either by itself or in addition to temporalis suspension and/or autologous fat grafting. Not only does the dermal fat graft create volume but it gives a normal texture to the contour. Implants used to create shape often result in a hard feel for the patient. The dermal fat graft gives a softer more normal texture which patients prefer.