Bone plates are implants that are used to stabilize and cover bone defects and fractures. Among which we particularly focus on the design and production of cranial and mandibular and hand-surgical implants. We incorporate our knowledge of the surgical application, manufacturing method, biomechanics and material characteristics into the design of the bone plates.
How do we design the plates?
We start the design with the computed tomography (CT) and the magnetic resonance imaging (MRI) data of the patient which we transfer to a segmentation software where the bone geometry is inspected and segmented. This geometry is the template on which the implant will be designed upon. After the exchange with the operating surgeon upon the proposed surgical procedure, our team of skilled CAD designers generate 3D implant designs using a variety of tools at hand for surgical planning. If the design is approved by the operating surgeon, the manufacturing process can begin. Here we have a variety of medically certified technologies we can use. Among the 3D printing technologies, Material Extrusion of high-performance polymers and Selective Laser Melting of titanium (Fachhochschule Nordwestschweiz) is most common. We can also use 3D printing to create a mold for injection molded implants, such as PMMA. After post-processing, quality inspection and cleaning of the manufactured implant, it is sterilized and packed, ready for surgery. After the surgery, if post-operative data is at hand, the team inspects and documents this.
Which rules need to be considered?
When designing implants for patients, we have numerous requirements to consider, among which are:
A ) Regulatory:
When designing patient-specific implants we need to comply with the regulations set in place for medical devices.
Next to evaluating among multiple treatment options if the solution is the best for the patient, we need to consider the surgical approach for implantation, e.g. possible fixation points for screws need to be accessible through the planned surgical approach.
C) Suitability of the material:
We need to make sure that the biomaterial used is suitable for implantation, does not cause any adverse tissue reaction (biocompatibility) and that it is medically certified.
The implants will often remain with the patient for a lifetime. This needs to be considered in the design and ensured that the implant can withstand the forces that it will be subjected to inside the body. Using computational modelling tools such as finite element analysis and the knowledge of the additive manufactured material and various biomechanical loading conditions, we can simulate patient-specific implant-bone constructs and evaluate areas of the implant and bone with high stress gradients. This virtual testing of implants is called in-silico validation. The weak or too bulky areas of the implant can be improved by changing the implant design, either through design changes made by the design engineer, or using a novel approach with algorithms such as topology optimization (Michaela's topic).
With additive manufacturing and surface processing and coating technologies, taking titanium as an example, we can create porous or rough surface structures that promote bone re-growth and in-growth, creating a stable connection between implant and bone. If the implant is to be removed e.g. osteosynthesis plates for bone fractures, we favor a smooth surface of the implant.
Next to practical considerations, we cannot underestimate the effects of aesthetics. It is important to adapt the implant to the surface of the patient’s bone contour. If possible, bone structure that has a symmetrical counterpart can be mirrored, if this is not possible, statistical shape models can be used as a reference.