Using Contemporary Technology

The design of engineering systems to fit the human body requires an interface with complex surfaces and materials and integration with the physiological and psychological entity that is the individual. While the human body is to some extent adaptive it can be argued that design, where the engineering solution is delivered within the constraints imposed by anatomy and physiology and pathological change to the tissue, is a preferred outcome. This applies in particular to an implant device that has intimate contact with tissue structures or an assistive device in rehabilitation that must seek to optimise residual capability. Computer assisted design, particularly where the anatomical shape data is available to the computer as a basis of the design, has particular merit.

The CITRA and Advanced Manufacturing groups use a suite of software programs in the design and manufacturing process, including:

• IMPAX – Picture archiving service for storing and viewing all radiological data (X-ray, CT, MRI, US) – used by all of WA Health
• Clear Canvas – Local storage and viewing of radiological data
• Materialise Mimics – software to create 3D objects from imaging data. Ability to do basic measurements of anatomy (in 2D and 3D) and add simple geometric shapes to medical data.
• Geomagic FreeForm Plus – software to manipulate 3D data, including cutting, sculpting, smoothing, etc. Particularly useful for non-parametric modelling.
• Solidworks – Engineering CAD package used to design devices or device components. Particularly useful for parametric modelling.
• Catalyst EX – Software for processing a 3D object, slicing it for 3D printing and sending it to a 3D printer
• GrabCAD Print – Software for processing a 3D object, slicing it for 3D printing and sending it to a 3D printer
• DeskProto –  Software for processing a 3D object and generating tool-paths for a CNC machine

A typical workflow in relation to implant manufacture is IMPAX > Clear Canvas > Mimics > Freeform and/or Solidworks > Catalyst EX or GrabCAD Print or DeskProto > 3D printer or CNC Machine. Commissioning of new 3D printers will see the upgrade of the current Catalyst EX and GrabCAD software.

3D printing and/or Additive Manufacturing (AM) is rapidly evolving as a credible technology for the production of accurate models, prototypes and for the direct manufacture of complex componentry. While the full potential for AM is somewhat limited by the materials available for printing, the mechanical properties of the fabricated article and their surface finish, the capacity to replicate complex shapes from CAD data nevertheless makes it ideal for anatomical modelling and for the prototyping of biomedical devices.

CITRA has been applying 3D techniques for the manufacture of implant devices from CT data for over thirty four years. Significant steps included:

• 1995: An adaptation of research software (Nuages, NIH Image) was developed in-house to form CAD surfaces/volumes from imported CT data. This was used to machine models in PVC using the CNC milling capacity in TSD as the template for manufacturing custom shoulder arthrodesis.
• 1997: PVC shape manufacture was adopted for the manufacture of titanium cranioplasty. The cranial surface was modelled using CAD to close the “defect” using symmetry data and smoothing, providing a template CNC machined in PVC as the pattern for use in hydrostatic pressing of the plate. Technique was based on development work carried out by colleagues in New Zealand.
• 1984: Fabrication of a model of scapular made from serial CT images, projected and indexed to provide a series of templates cut from 3mm acrylic sheet and stacked to form the shape upon which the custom plate was fashioned in 316 stainless steel using conventional manufacturing techniques.
• 1998: RPH was instrumental in supporting the introduction of Stereo-lithography into WA, based on its possible application in anatomical modelling and custom implant manufacture. While technically appropriate, build times and cost proved problematic and alternatives from the evolving fused deposition modelling (FDM) and selective laser sintering (SLS) were considered for future application.
• 2006: In response to a number of difficult pelvic reconstruction cases, work was conducted with SLM Solutions GMBH to develop and manufacture custom acetabular cages in sintered titanium, designed to support a conventional hip arthroplasty
• 2013: A second instrument was introduced to ensure service continuity to clinical services including Neurosurgery, Orthopaedics and Maxillofacial Surgery, increasingly reliant on the custom service.
• 2018: New technology: CITRA is introducing additional 3D printing and MultiJet (MJP) capacity that will further secure the clinical service and facilitate innovation with additional material options. The new technology introduces rigid, polymeric and elastomeric capability with build volumes in the range of 300 x 200x 150 mm and colour adding versatility in anatomic modelling and tissue discrimination.

Surface scanning techniques are used routinely to replicate body shapes and soft tissue surfaces that form the interface for the custom design of prosthetic, orthotic and other assistive devices.

Current technologies include:

• Eva 3D Scanner. Four devices using white light technology are used routinely to provide surface shape data for the custom manufacture of orthotic devices (spinal jackets used in cases of spinal trauma, surgery and scoliosis management, ankle-foot orthoses, protective helmets). Use in cases requiring pressure management and specialised seating and for amputee prosthetic devices are also applicable. 3D resolution up to 0.5mm and with point accuracy up to 0.1mm is typical and a 3D accuracy of 0.03% over a scanning distance of 100cm allows work within reasonable proximity to the patient.
   
   
   
• Space Spider Scanner. The Space Spider using blue light technology provides the special resolution and accuracy required for prosthetic replication of soft tissue structures in plastic surgery and facial-maxillary surgery. 3D resolution of 0.1mm with a point accuracy of 0.05mm are suited to applications requiring the replication of complex geometries and sharp edges often required in such cases (e.g. ear and nasal prostheses: refer Clinical innovations, circa 2016.)

Medical Engineering and Physics manufacturing facilities are being progressively upgraded to reflect contemporary trends toward computer assisted machining (CAM) and digital manufacturing. This is reflected in lathe (turning), milling and sheet fabrication technologies.

Recently the Orthotic and Prosthetic (O&P) team has made a transition from conventional manufacturing techniques to a digital methodology using scanned data from the patient and robotic machining to form the patient template.

O&P manufacture has followed the traditional methods where the device (e.g., ankle-foot orthosis or spinal jacket etc.) is hand manufactured using moulding techniques based on a corrected plaster cast taken from the patient. The cast requires taking a plaster facsimile of the patient’s body shape using conventional bandaging techniques and developing the shape facsimile by backfilling the cast with plaster to form the patient template. Clinical corrections (e.g. relief of adverse pressure points or the application of pressure to apply correction) are applied and the orthosis is manufactured by hand, using vacuum and/or drape moulding techniques, trimming to fit the patient and the addition of accessory components such as straps.

The O&P team has made a transition to contemporary digital techniques for the manufacture of orthotic appliances in 2017. Plaster casting to create shape template against which the orthosis is manufactured is being replaced by a method using digital 3D scanning to map the body shape (refer to section on Surface Scanning), modification of the surface shape to apply clinical corrections, using boutique (Rodin) computer assisted design (CAD) software and the digital manufacture of the template using robotic manufacture. The new technology has been adopted by the Rehabilitation Technology Unit (RTU) O&P team and by the Perth Children’s Hospital group using the orthotic manufacturing facilities based at Royal Perth Hospital.

Transition to the new methodology requires a quantum change to practice and its introduction has been gradual to allow retaining and familiarisation and to develop confidence that the clinical outcome is at least equivalent to established techniques. Emphasis has centred on the spinal orthosis due to the specialist services provided by the RTU in relation to spinal trauma (based at Royal Perth Hospital) and the management of scoliosis using conservative bracing techniques and surgery (based at Fiona Stanley and Royal Perth hospitals respectively).

The new technology is proving effective in:

• Reducing the impact on the patient by using a non-contact surface mapping technique when compared with plaster casting the torso in a prone or supine position on a Risser frame and applying pressure correction during the casting process.
• Significantly reducing the procedural times and staff needed for the casting process.
• Enabling scanning of the patient in bed or at the bedside.
• Enabling cost effective replication/modification of the template without the trauma to the patient of repeat casting.
• Reducing storage overheads substituting data file storage for holding the as cast template for possible future use or reference.
• Demonstrating the potential for scanning of the patient in remote centres, reducing the need to travel to the clinical or manufacturing centre. Potential cost savings and service efficiency are anticipated for WA in this regard.