Evolution of design considerations in complex craniofacial reconstruction using patient-specific implants

Previously published evidence has established major clinical benefits from using Computer Aided Design (CAD), Computer Aided Manufacturing (CAM), and Additive Manufacturing (AM) to produce patient-specific devices. These include cutting guides, drilling guides, positioning guides, and implants. However, custom devices produced using these methods are still not in routine use – particularly by the UK National Health Service (NHS). Oft-cited reasons for this slow uptake include: a higher up-front cost than conventionally-fabricated devices, material-choice uncertainty, and a lack of long-term follow-up due to their relatively recent introduction. This paper identifies a further gap in current knowledge – that of design rules, or key specification considerations for complex CAD/CAM/AM devices. This research begins to address the gap by combining a detailed review of the literature with first-hand experience of interdisciplinary collaboration on five craniofacial patient case-studies. In each patient case, bony lesions in the orbito-temporal region were segmented, excised, and reconstructed in the virtual environment. Three cases translated these digital plans into theatre via polymer surgical guides. Four cases utilised AM to fabricate titanium implants. One implant was machined from PolyEther Ether Ketone (PEEK). From the literature, articles with relevant abstracts were analysed to extract design considerations. 19 frequently-recurring design considerations were extracted from previous publications. 9 new design considerations were extracted from the case studies – on the basis of subjective clinical evaluation. These were synthesised to produce a design considerations framework to assist clinicians with prescribing and design engineers with modelling. Promising avenues for further research are proposed