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control anatomical references that are identified
manually. Such procedure is time consuming, leaves
imperfections in the prosthesis surface and greatly
depends on the physician’s experience. Moreover,
most of these orthosis are modelled independently of
the symmetric defect and do not take into
consideration the thoracic wall shape. Consequently,
this process often produces non-uniform strength
distributions, misalignments and offsets between the
orthosis and the patient thoracic wall (which end up
producing initial discomfort), thoracic pain,
increased patient adaptation time and decreased
cosmetic outcome of the deformity. To overcome
current orthosis practice disadvantages, this work
proposes a systematic methodology for the
personalisation of a Pectus Carinatum orthosis. The
orthosis size and curvature are automatically
determined using information retrieved by CT
imagiology or a 3D scanner of the thoracic wall
shape.
An array of points containing this virtual model
information is input to the (Vilaça et al., 2009)
system to automatically bend two stainless steel
braces (AISI type 316LVM (low carbon vacuum
melt), corresponding to the anterior and posterior
orthosis braces. The differences between the virtual
and physical braces were determined by modelling
and bending 15 orthosis using 15 CT data sets of
patients with Pectus Carinatum, acquired at São
João Hospital of Porto (Portugal). To measure these
differences, an LVTD (linear variable differential
transformer) was used to compare, at different bend
times, the differences between the virtual point and
curvature, with the real values. Results show that no
significant differences exist concerning the curvature
angle and size of the orthosis, given that all errors
are below 10 µm.
Recently, this personalized orthosis has been
modelled for two patients whose thoracic wall
showed symmetric (Figure 1 - B) and asymmetric
defects (Figure 1 - A). For both patients, the orthosis
suitably fitted the thoracic wall shape, and the
pressure of the cushioned compression plates was
adequate to prevent slippage. The pressure of
treatment is controlled using an electronic pressure
sensor whose output value is shown on an LCD
(PMD in Figure 4). This permits to adjust the
correction pressure to the desired level and prevents
from making too much pressure, which could cause
pressure necroses.
Such results indicate a considerable step forward
that might decrease the need of open surgery for a
nonoperative approach in Pectus Carinatum
deformity correction. In addition, nonoperative
management offers a significant cost benefit since
with this new method, hospitalization time, per-
operative and post-surgical complications are
eliminated.
ACKNOWLEDGEMENTS
The authors acknowledge to Foundation for Science
and Technology (FCT) - Portugal for the fellowships
with the references: SFRH/BD/74276/2010;
SFRH/BD/68270/2010; UMINHO/BI/95/2012; and,
SFRH/BPD/46851/2008. This work was also
supported by FCT R&D project PTDC/SAU-
BEB/103368/2008.
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