Orthoses Design and Manufacture
Numbers in the text correspond to numbers on the flow charts.
CAD/CAM (12) is an acronym for computer-aided design/computer-aided manufacturing – computer systems used to design and manufacture products. The term CAD/CAM implies that an individual can use the system both for designing a product and for controlling manufacturing processes.
In order to design a custom foot orthosis, it is imperative to have a detailed and accurate prescription and cast.
Based on the findings of the full clinical assessment, biomechanical examination, and gait analysis, the foot care professional will create the prescription for the custom foot orthosis, which is actually the detailed instruction on how the orthosis is to be made. The prescription specifically outlines the parameters of design, materials, composition, and fabrication of the orthosis intended to treat the patient’s unique medical needs.
After choosing the best casting method to capture the patient’s foot, the next phase involves the preparation of the cast or scan to ensure the actual orthosis is shaped to support, correct, or accommodate the foot structure and provide comfort during use. Cast dressing or modifying refers to this preparation in addition to excavations and additions to accommodate deformities and prominences, a process that can be performed manually (13) using hand-carved plaster from a physical cast (plaster or sock slipper casting, foam box casting, wax), or digitally (14) where a technician manipulates a scan using a computer program (contact digitization, laser/optical scanning).
To satisfy the custom-manufactured criteria using digital design, each scan must be processed individually and not be subject to batch processing, library1, or best-fit systems (15). The final scan file must be unique to the individual throughout the entire process of manufacturing the orthosis.
Once the design phase is completed, the orthosis’s raw material is either vacuum-pressed (16) over a cast for manual design and manufacture, or the manipulated scan file is sent to a 3D milling machine (17) or a 3D printer (18).
To be considered custom-made, a foot orthosis must be fabricated from raw materials and made directly on a foot cast that captures the anatomy and contours of the plantar aspect of the foot as defined by the 3D casting criteria.
Currently, the acceptable manufacturing techniques that can be utilized to fabricate the orthosis shell and/or posting on or from the 3D cast using the raw materials include:
Vacuum forming (16): Sheets of thermoplastic material are heated to a forming temperature and stretched over the mould made from the cast to create the shell/footbed of the orthosis. Suction is applied to shape the material to the mould.
Milling/routing (subtractive manufacturing) (17): A CNC (computer numeric controlled) machine uses a router to carve a positive foot cast used for vacuum moulding or carve an orthosis directly from a variety of materials. Alternatively, a 3D physical cast may be scanned in order to create a digital copy of the cast (2b).
3D printing (additive manufacturing) (18): Most methods of 3D printing can be used in orthosis manufacturing. Fused deposition modelling (FDM) and Polyjet printers layer small jets of plastic through a nozzle to build an orthosis while selective laser sintering (SLS) uses lasers to cure or sinter a powdered material into the shape of an orthosis.
1 Library in this case refers to “pre-made” moulds that are not custom made from the individual contours of the patient’s foot. These moulds are kept as a “library” of moulds of various foot shapes and sizes and are matched up and used as approximations of the patient’s foot architecture.