06-11-2012, 12:56 PM
Virtual 3D Planning and Guidance of Mandibular Distraction Osteogenesis
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ABSTRACT
We present a system for 3D planning and pre-operative rehearsal of mandibular distraction osteogenesis
procedures. We describe two primary architectural components: a planning system that allows geometric
bone manipulation to rapidly explore various modifications and configurations, and a visuohaptic simulator
that allows both general-purpose training and preoperative, patient-specific procedure rehearsal. We
provide relevant clinical background, then we describe the underlying simulation algorithms and their
application to craniofacial procedures.
INTRODUCTION
Distraction Osteogenesis
The treatment of patients with complex anatomical
deformities that are caused by trauma or congenital
defects is one of the most challenging
multidisciplinary tasks in medicine. Due to the
introduction of plating systems and changes in
surgical technique in the last 20 years, correction
of severe malformations has become possible.
Such procedures are generally performed by highly
specialized teams, frequently in a single operation.
Distraction osteogenesis is gaining
popularity as a common treatment for facial
deformities. Such procedures aim to lengthen and
reform the diseased or damaged portion of the
mandible by performing one or more osteotomies
(surgically-induced bone fractures), manipulating
the resulting bone fragments into more a desirable
configuration, and “growing” the mandible
through daily distraction.
Virtual Planning
The goal of a surgical plan in reconstructive
surgery is the normalization of the shape,
symmetry, dimension, and function of hard and
soft tissue. At present, surgical plans and surgical
outcomes are analyzed on 2D and 3D radiographs
and photographs. As much of the challenge in
trauma surgery lies in the understanding of relative
spatial positions of critical vascular, neural and
other structures in relation to the underlying bone
and to the facial surface, recent developments in
imaging techniques have allowed more effective
pre-surgical diagnosis and surgical planning using
patient-specific data.
VIRTUAL PLANNING ENVIRONMENT
Overview
We begin with a discussion of our interactive
planning system, which allows the manipulation of
real patient data before surgery and provides semiautomatic
determination of a healthy template for a
diseased mandible. The description uses the
surgical correction of hemi-facial microsomia – a
condition in which the mandible is unilaterally
diseased and/or deformed – as a context and
running example. Patients presenting with this
condition are often considered candidates for
distraction osteogenesis, so it is an appropriate
example.
Planning for this condition also makes
optimal use of the mirroring techniques
incorporated into our system, which allow the
surgeon to use a mirrored version of the healthy
side of the mandible as a template for planning
distraction for the diseased side. The distraction
planning techniques discussed herein may be used
in other cases as well, if both sides of the mandible
are diseased or if the surgeon does not wish to use
the healthy side as a template.
Automatic Vector Determination
The next stage in a distraction procedure is the
placement of the distraction apparatus. Currently, a
surgeon uses personal expertise to determine the
path through which the bone will travel during
distraction and the daily rate of distraction. This
desired path must be translated into the position
and orientation of the physical distractor. To
provide the reader with a general orientation and a
sense of scale, Figure 4 depicts an infant with a
physical distractor.
In some cases, the desired movement of the
bone is restricted to translation – movement along
a straight line in three dimensions. In this simple
case, a standard distractor can be used and the
distractor is advanced at a constant one millimeter
per day.