be designed in a way that the contour of the surrounding skull bone is followed. Small defects of <5 cm2 have an almost flat surface, whereas large defects require a more sophisticated implant, which has implications on the design procedure.

Defects that cross the midline pose more problems when designing the implant, since information on the contour of the contralateral side of the skull is missing and, thus, mirroring of the contralateral curvature is not possible. Designing an implant that involves part of the orbit is more complicated because of the curvature of the orbital area and the need for mirroring of the other side. The anatomical location of the defect is, of course, also important, since the bone thickness varies along the skull. The thickness of the bone has to be taken into account when designing the implant, especially the part that will be fixed to the skull bone. The proposed classification divides skull defects into six distinct classes, based on the difficulty of implant design. A skull defect is described by the class it belongs to and its anatomical location.

15.2.1.1  Examples

Patient 1 had undergone previous surgery for removal of a meningioma, with creation of a defect at the left parieto– occipital area of the skull (Fig. 15.1a–d). The skull defect was classified as a Class II occipital skull defect. Design and manufacturing was based on a multispiral computer tomography (CT) scan (Toshiba, Japan). The scan data were converted into a stereolithographic (STL) data set using the computer program Mimics (Materialise, Leuven, Belgium). The STL data were imported in 3Matic (Materialise, Leuven, Belgium) and further processed on a Pentium IV workstation. It was decided to manufacture a titanium implant, using high-speed milling (HSM).

Patient 2 had undergone surgery for decompression of the brain after severe trauma. A part of the skull bone became necrotic, leaving a large skull defect at the right

side (Fig. 15.2). The skull defect was classified as a Class III temporo-parietal skull defect. The computeraided design resembled the procedure in case 1. The implant, however, was manufactured by selective laser melting with titanium powder (SLM).

The implant in patient 1 was designed in 3 h with the help of surface guidelines and mirroring of the contralateral side (Fig. 15.1b) (Hutmacher et al. 2004). Four fixation lips on the implant were designed to allow fixation to the skull. The implant (Fig. 15.1c) was milled out of medical grade 5 titanium block in a five-axis HSM machine in 48 h (IDEE, MUMC Maastricht University Medical Centre, Maastricht, The Netherlands). The implant was fixed with four titanium screws (length 3 mm, diameter 1.5 mm, KLS Martin, Tuttlingen, Germany) to the remaining skull (Fig. 15.1d).

The implant of patient 2 was designed in 16 h with the help of surface guidelines and mirroring of the contralateral side. Five fixation lips on the implant were designed to allow fixation to the skull. The implant (Fig. 15.2b, c) was manufactured out of medical grade 5 titanium alloy by Electron Beam Melting (Arcam, Sweden) in 12 h. The implant was fixed with five titanium screws (length 3 mm, diameter 1.5 mm; KLS Martin, Tuttlingen, Germany) to the remaining skull (Fig. 15.2d).

15.2.2  General Health Status

The medical history of the patient as well as size and localization of the defect are crucial elements for the determination of the treatment plan. The anamnesis must consider the exact medical history of the patient, as different defect causes — trauma, tumor, infection, neurological diseases, apoplectic insults, malformation — may lead to a different evaluation and treatment plan.

Coexisting medical problems may even prevent any further attempt at reconstruction:

•Age, life expectancy and prognosis

•Severe medical disorders

•Multiple treatment failures due to infections or others

•Anticoagulative medical treatment

•Deficits in cooperation

•Alcohol or drug abuse

The duration of the operation plays a considerable

role in the reduction of risks. It reduces the blood loss and the risk of brain swelling, the infection risk and the risk of tissue damage. The indirect reconstruction of defects using prefabricated allogenic implants reduce the operation time, whereas a direct reconstruction with autogenous bone material causes higher morbidity and is more time-intensive due to harvesting the bone specimen.

There are, however, patients where no further attempt atreconstructionshouldbeconsidered.Thesearepatients with a clearly reduced life expectancy or patients that do not accept any reconstruction. Drug or alcohol abuse may be further contraindications for reconstruction. In patients suffering from apoplectic insults or intracranial bleeding with a high risk of thrombosis or embolism, the surgical risk and the method of reconstruction must be calculated with respect to the anticoagulative therapy. In this group of patients, allogenic implants are advantageous as the surgical intervention should be limited to the defect reconstruction. A limited surgical intervention with an acceptable duration of the operation will help to reduce bleeding to a minimum. Nevertheless, the risk of thrombembolism must be respected and evaluated as a surgical intervention is planned. A preventive low­ -dose

As soft tissue coverage is essential for success with allogenic and autogenous materials, it may in some rare cases not be advisable to reapproach these patients again with a surgical solution. For these patients, helmets and epithetic applications help to reduce the risk of injury and improve the aesthetic appearance.

Aesthetic rehabilitation due to skull form may be another indication for reconstruction, especially in pat­ ients with no or few neurological deficits (Blake et al. 1990; Eufinger and Wehmöller 1998, 2002; Poukens et al. 2008).

Neurological deficits may be the consequence of skull bone trauma, intracranial tumors or apoplectic insults. Besides the general medical status of the patient the necessity, urgence, and method of skull bone reconstruction depend on the patient’s neurological status. The neurological deficit can result from the disease leading to the skull bone defect, but also from the defect itself. To detect and evaluate the skull bone defect as primary or additional cause for a neurological deficit, however, is difficult. Nevertheless there is a need for reconstruction of skull bone defects to improve the individual’s neurological situation and protect the brain from further damage. The neurological deficits can be temporary, long lasting or even progressive. Traumatic brain injuries may heal without consequences, but in 35% of the cases with open brain traumas traumatic epilepsy develops (Poeck 1987). Nearly 95% of these traumatic epilepsies develop in the first two posttraumatic years (Poeck 1987).

The most obvious indication for skull bone defect reconstruction is to prevent further damage to the patient. Sensory or motor deficits, hemi-, or paraplegic paralysis, epileptic attacks or infections will lead to a progressive loss of motor and sensory function and control. Medical treatment and rehabilitation will result in a sensory-motor improvement or stabilization in many patients.

The better the functional results are, the more urgent is the need for a skull bone reconstruction, especially in large bone defects. This implies that the reconstruction of skull bone defects is necessary to avoid any further traumatic brain damage resulting from a direct trauma to the brain (Poeck 1987).

In patients with long-persisting neurological deficits the rehabilitation efforts may be supported by the reconstruction of skull bone defects in two ways:

1.The integrity of the skull lowers the risk of a further injury

2.The skull bone reconstruction itself may improve the neurological status

Suboptimal outcomes are not as uncommon as they should be. Careful assessment and analysis of the existing treatment deficit including three-dimensional CT scans and soft tissue evaluation, as well as careful followup and audit will establish their full extent. Inadequately treated craniofacial defects can result in significant cosmetic deformity and functional disabilities, which are extremely difficult to correct. If possible, a simulation of the intended reconstruction should be performed to compare different treatment options.

To re-establish a maximum of quality-of-life, function, social acceptance and self-esteem, every reasonable effort should be undertaken to correct and improve a patient’s situation and individual cranio-maxillofacial defect. In some cases, a craniofacial implant must be inserted as a prerequisite for further epithetic reconstruction as shown below.

A serious evaluation and discussion with the patient may in some cases lead to the conclusion that no reconstruction should be attempted. This should be considered, if it is the patient’s wish and the technical possibilities cannot be harmonized to reach a treatment goal which is acceptable to the patient (Fig. 15.3).

15.2.5  Treatment Plan

A team of specialists has to be at hand to perform the planning, designing, and manufacturing of the implant and reconstruction of the defect. As each step of the procedure has to be validated, a close cooperation between the partners is an absolute necessity for a good result.

The ideal team consists of:

•Cranio-maxillofacial reconstructive surgeon/neuro­ surgeon

•Radiologist

•Engineering team for design and preparation of data sets

•Engineering team for manufacturing of the implant

Fig. 15.3  (a) Rapid prototyping model shows the large craniofacial bone defect. (b) Implant for the reconstruction of the lat- ero-orbital defect. (c) Control X-rays after implantation. (d)

Patient before and after reconstruction with titanium implant and epithetic reconstruction of the orbit

•Sterilization unit

•OP capacity with experienced anesthetist and nursing staff

•Intensive care unit

In an ideal setting, the cranio-maxillo-facial surgeon

and neurosurgeon work together as a team to perform the reconstructive surgery. The team leader is responsible for the data acquisition, product planning and production of the implant. The leading reconstructive surgeon has to validate the production process step by step, as the engineering teams usually have no direct contact

with the patients. He has to organize the whole procedure with respect to the operation date. The production process, the material used, the methods of manufacturing, sterilization of the implant and the transport of the sterilized implant to the operation room must follow a certified pathway. It must be guaranteed that each step of the production process is documented according to internationally accepted quality standards. The whole process from data acquisition to the operation may take at least 6 weeks. Figure 15.4 shows a diagram of the treatment plan.