Biomedical Engineering Reference
In-Depth Information
craniofacial skeleton has gained wide acceptance, since its clinical introduction by
McCarthy et al. [
51
], due to the huge possibilities this process offers. Previous stud-
ies of mandibular distraction osteogenesis have characterized the local bio-physical
environment created within the osteotomy gap at different time points [
5
,
13
,
44
,
49
,
59
,
63
] or during the whole process of distraction through mechanobiological
models [
6
,
7
,
60
]. Reina-Romo et al. [
60
] studied the temporo-spatial evolution of
the different tissues during distraction osteogenesis and the biomechanics in patients
with severe deformities. The aim of this section is to review this work, in which the
previously developed model of distraction osteogenesis [
56
] is used to investigate its
ability to predict the main tissue patterns during the course of the three dimensional
lengthening procedure of the mandible ramus.
This study was based on data from a 6-year-old male patient with unilateral
mandibular hypoplasia of the right mandibular ramus, corresponding with a grade
IIb according to Pruzanski criteria. This pathology is known as hemifacial mi-
crosomia (HFM) and consists of a congenital asymmetrical malformation of both
the bony and soft-tissue structures of the cranium and face. The three-dimensional
model of the mandible corresponded with the original morphology of the mandible
before treatment. Four different regions were identified during the segmentation
procedure of this model: gap, cancellous bone, cortical bone and teeth. The right
ramus of the model was virtually cut simulating the osteotomy at the location
indicated by the surgeon. With regard to the clinical distraction protocol, the full
process includes a 7-day latency period and a phase of distraction of 20 days.
Figure
6
shows the evolution of the tissue distribution in the mandible through
the process of distraction. It can be observed how this tissue distribution varies
significantly. In the first days of the process the gap is mostly filled by damaged
debris tissue, due to the high values of the mechanical stimulus. During the initial
stage (1-10 days), tissue damage is gradually repaired due to the decreasing values
of the strain magnitudes allowing granulation tissue to be deposited (Fig.
6
). This
granulation tissue is synthesized by MSCs that migrate from the marrow cavity,
periosteum and surrounding soft tissues to the interfragmentary gap. By day 10,
the first islands of cartilage tissue begin to appear within the distracted gap. As
distraction proceeds, the low stimulated mechanical environment around the two
bone fragments favor the formation of bone tissue. From day 15 until the end of
the distraction process more amount of cartilage can be seen in the outer part of
the callus. Immediately following completion of 20 mm, the distraction outcome
shows a gap filled with cartilage tissue, which constitutes most of the regenerate
surface. The area of new bone formation was located close to the host bones and the
remaining gap was filled with cartilage tissue.
This model presents a preliminar three dimensional approach of distraction
osteogenesis from a computational perspective. Although it should be further
extended in the future, it shows the enormous potential it offers. It could be used
to study different aspects of the distraction procedure such as the effect of the
distraction rate, the best placement of the corticotomy or the time of the device
removal amongst others once the model parameters have been adjusted.
