Optimizing cranial implant and fixture design using different materials in cranioplasty

Cranial implants are used to secure intracranial structures, reconstruct the skull contour, normalise cerebral hemodynamic, and repair cranial defects. Larger bone defects require intervention for repair from an implant made from autologous bone or other material. To repair such defects using implants, materials necessitate biocompatibility with the natural bone. Patient Specific Implants (PSI) are designed to repair specific cranial defects following standard procedures for implant design, fabrication and cranioplasty. Autologous bone, bone cement comprising HydroxyApatite (HA), Poly methyl methacrylate (PMMA), Medical Grade Titanium Alloy (Ti-6Al-4V) and Polyether-ether-ketone (PEEK), are widely used to fabricate PSI for repairing different types of bone defects. To optimize a PSI for shape, size and weight, it is essential to design the implant using 3D modelling and fabrication techniques. Effective attachment of an implant material with a defective skull is also influenced by the joints and fixture arrangements at the interface, these fixtures can be of various types, materials and have different joining procedures. In this study, a comparative analysis of different cranial implant materials (Autologous Bone, PMMA, PEEK and Ti-6Al-4V) attached to a defective skull with Ti-6Al-4V and PEEK fixture plates has been performed, using Finite Element Analysis (FEA). Two types of fixture designs were used as Square 'X' and Linear shapes, which were fixed along the interface between implant and the skull. Four fixture plates were fixed symmetrically along the boundary for maximising stability. The findings suggested that all the implant materials were able to sustain extreme boundary conditions such as external loads of 1780N and IntraCranial Pressure (ICP) of 15mmHg without failures. PEEK implants exhibited 13.5 % to 35% lower von Mises stresses in comparison to autologous bone implants and Square 'X' fixture design provided higher stress relieving results in comparison to Linear fixtures by nearly 18.4% for Ti-6Al-4V fixture material and 10.9% for PEEK fixture material, thereby, encouraging PEEK as an alternative to conventional cranial implant and fixture materials