R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

Case studies 151
manner. The software also allows the import of scan data to create reference
objects or ‘bucks’ onto which objects may be designed.
The data of the patients’ anatomy was imported into the software. The
surgery is then planned and simulated by using the software tools to position
prostheses and implants or to cut the skeletal anatomy and move the
pieces, as they would be in surgery. When the clinicians were satisfi ed with
the surgical plan the surgical guides were designed to interface with the
local anatomy.
In general, the surgical guides were designed by selecting the anatomical
surface in the region of the surgery (drilling or osteotomy) and offsetting
it to create a structure 1–2 mm thick. The positions of the drilling holes or
cuts are then transferred to this piece by repeating the planned surgical
procedure through it. Other features may then be added, such as embossed
patient names, orientation markers or handles. When the design is completed
to the clinicians’ satisfaction, the human anatomy data is subtracted
from the surgical guide as a Boolean operation. This leaves the surgical
guide with the fi tting surface as a perfect fi t with the anatomical surface.
Typically, the curvature and extent of the fi tting surface provide accurate
location when it is fi tted to the patient. The fi nal design is then exported as
a high quality STL fi le for rapid manufacture by Selective Laser Melting
(SLM TM ). SLM TM is described in Section 5.5.3.
Step 3: Rapid manufacture
In order to build surgical guides successfully on the MCP Realizer SLM
machine (MCP-HEK GmbH SLM Tech Center Paderbom, Hauptstrasse
35, 33178 Borchen, Germany) adequate supports had to be created using
Magics software (Version 9.5, Materialise NV) The purpose of the supports
was to provide a fi rm base for the part to be built onto whilst separating
the part from the substrate plate. In addition, the supports conduct heat
away from the material as it melts and solidifi es during the build process.
Inadequate supports result in incomplete parts or heat induced curl, which
leads to build failure as the curled part interferes with, or obstructs, the
powder recoating mechanism.
Recent developments in support design have resulted in supports that
have very small contact points, which has improved the ease with which
supports can be removed from parts. However, the parts were all oriented
such that the amount of support necessary was minimised and avoided the
fi tting surface of the guide. This meant that the most important surfaces of
the resultant part would not be affected or damaged by the supports or
their removal.
The part and its support were ‘sliced and hatched’ using the SLM TM
Realizer software at a layer thickness of 0.050 mm. The material used was