Page 195 - Clinical relevance of current materials for cranial implants
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                                General discussion and future perspectives
The objective of this thesis was to identify and to fill gaps in the current understanding of techniques and materials for cranioplasties by analyzing the available evidence and systematically collecting and evaluating data. We made a step forward towards the prerequisites and development of a new material for cranioplasties. Despite the new findings in this thesis, our research has not yet standardized the management of cranioplasties. Literature research was often restricted by studies with small patient samples, the inability to carry out a study that would offer convincing evidence, and the limited amount of currently available evidence regarding cranioplasties. This hinders clinical practice, but also complicates the design and execution of methodologically sound studies on cranioplasties. In this chapter, we reflect on our research findings and offer some possibilities for future developments, in which several challenges must be overcome.
Lack of definitions, protocols and guidelines
One of the main findings in this thesis is that there is no standard treatment and no standardized or generally accepted protocol for decompressive craniectomy nor cranioplasty.
The available literature shows that the definition of complications, including infection and resorption, diverges widely1,2. Multiple factors need to be considered according to the nature of the cranial defect and the medical prognosis; systemic and local factors; size and form of the defect; goals of the reconstruction (protection and/or cosmesis), the choice of material and the manufacturing process.
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One of the materials mostly used for cranioplasties is autologous bone. Autologous bone is associated with high resorption rates3. A commonly described definition for resorption discerns two types of resorption: thinning of the bone mass on imaging or by palpation (type I), and complete lysis of the inner and outer tabulae with loss of cerebral protection, requiring revision (type II)2,4. Most patients do not undergo a standardized follow-up CT-scan, unless the patient experiences symptoms, as pain, discomfort or cosmetic impairment. The lack of a standardized follow-up protocol including a CT-scan leads to underreporting of resorption rates. The resorption process differs among patients: some patients will not notice any resorption of the autologous bone at all and if a patient is asymptomatic, the need for a routine post-operative CT- scan in the follow-up is debatable.

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