R_Bibb_Medical_Modelling_The_Application_of_Adv.pdf

150 Medical modelling
use of metals also enables surgical guides to be made much smaller or
thinner whilst retaining suffi cient rigidity. This benefi ts surgery as incisions
can be made smaller and the surgeon’s visibility and access is improved.
6.6.3 Methods
To date three surgical guides have been designed and produced as described
here and subsequently used in theatre. The fi rst case was a drilling guide
for osseointegrated implants to secure a prosthetic ear. The remaining two
cases were for osteotomy cutting guides for the correction of facial deformity.
This section describes the general approach to the planning, rapid
design and manufacture of surgical guides. The following section describes
an individual case where the approach has been successfully employed for
an osteotomy.
Step 1: three-dimensional CT scanning
The patients were scanned using three-dimensional computed tomography
(CT) to produce three-dimensional computer models of the skull (see
Section 2.2). The CT data was exported in DICOM format, which was then
imported into medical data transfer software (Mimics, Materialise NV,
Technologielaan 15, 3001 Leuven, Belgium, www.materialise.com). This
software was used to generate the highest possible quality STL data fi les
of the patient’s anatomy using techniques described in Chapter 4. The STL
fi les were then imported into the computer-aided design (CAD)
software.
Step 2: Computer-aided surgical planning and design of the surgical guide
The CAD package used in this study (FreeForm ® , SensAble Technologies
Inc, 15 Constitution Way, Woburn, MA 01801, USA, www.sensable.com)
was selected for its capability in the design of complex, arbitrary but welldefi
ned shapes that are required when designing custom appliances and
devices that must fi t human anatomy. The software has tools analogous to
those used in physical sculpting and enables a manner of working that
mimics that of the maxillofacial prosthetist working in the laboratory. The
software utilises a haptic interface (Phantom ® Desktop TM haptic interface;
SensAble Technologies Inc.) that incorporates positioning in threedimensional
space and allows rotation and translation in all axes, transferring
hand movements into the virtual environment. It also allows the
operator to feel the object being worked on in the software. The combination
of tools and force feedback sensations mimics working on a physical
object and allows shapes to be designed and modifi ed in an arbitrary