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INNOVATION
3Dprintinginnovation inmedicalimplants
Ed Littlewood, from Renishaw’s medical and dental products division, discusses medical applications of 3D printing and the potential of the technology to improve procedures and aid patient recovery.
3D printing is used in industrial applications for prototyping and manufacturing. The technology uses a range of materials including polymers, ceramics, resins, stainless steel, cobalt chrome and titanium. Metal 3D printing is also known as additive manufacturing (AM). The additive manufacturing process produces a 3D object from a digital computer-aided design (CAD) file. Objects are built in layers, adding material until they are complete. This method offers great design flexibility, which means that highly accurate, bespoke and customised objects can be produced at low cost. The medical application of additive manufacturing is growing and current uses include: craniomaxillofacial (CMF) devices, hip and knee implants, spinal fusion implants, heart stents, neurological drug delivery and external prosthetic limbs. A significant benefit of the technology is the ability to customise and personalise the items produced so that they are patient specific. A number of UK NHS hospitals have used additive manufacturing to improve predictability, accuracy, safety and efficiency. Advances in the technology have inspired a number of surgeons to commission additive manufactured, patient specific implants (PSIs) and surgical guides.
Patient specific implants (PSIs)
Additive manufacturing of patient specific implants uses a digital workflow that can benefit several stages of the process including planning. To produce a patient specific implant, data is acquired from a patient scan, such as a CT or MRI scan. The patient’s data is then imported into CAD, prepared for manufacture, made and then finished.
One such application of additive manufactured implants is in craniotomy and cranioplasty, when a patient has a piece of skull removed to accommodate swelling caused by injury, tumour or stroke. The patient then requires the surgical repair of the bone defect to restore the skull. The
FEBRUARY 2017
Pre and post cranioplasty comparison
surgical repair can be done by replacing the original bone section, or by using a custom implant. If the surgeon chooses a custom implant, it is important that the implant fits correctly, particularly for aesthetic purposes. The customisation possible with additive manufacturing allows accurate bespoke implant production. This is an advantage for this application because of the irregular shapes of skulls, which makes implants difficult to standardise. Furthermore, the skull and brain are complex and difficult areas to visualise.
A traditional approach to PSI for cranioplasty would be to form the titanium into shape using a hydraulic press; this would be formed on a model taken from an impression of a patient’s skull. The impression is taken over the skin, which means it is subject to some inaccuracy as the implant will be placed directly on the bone. Alternatively, a plate formed from polymethyl methacrylate (PMMA) could be created during the surgery, which adds time to the procedure, or it could be formed prior to
surgery, although this requires a more complex sterilising method, as PMMA cannot be autoclaved.
Using a custom, additive manufactured implant offers potential for decreased surgical time and improved implant fit by addressing some of the disadvantages of the aforementioned traditional approaches. However, the real innovation of additive manufacturing for PSI comes in the shape of custom guides. When implanting a PSI, in some cases it might not be obviously located due to a lack of landmarks on the patient’s bone. In this situation, the surgeon can use a placement guide to locate the implant into its correct position. Surgeons can also use an additive manufactured cutting guide during a surgery to harvest bone accurately. Finally, using a cutting guide can also allow bones to be cut with better precision, giving greater surface area contact between mating surfaces, which leads to better osseointegration. Adopting additive manufacturing technology can help reduce surgery time.
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