Computer-aided position planning of miniplates to treat facial bone defects

In this contribution, a software system for computer-aided position planning of miniplates to treat facial bone defects is proposed. The intra-operatively used bone plates have to be passively adapted on the underlying bone contours for adequate bone fragment stabilization. However, this procedure can lead to frequent intra-operatively performed material readjustments especially in complex surgical cases. Our approach is able to fit a selection of common implant models on the surgeon's desired position in a 3D computer model. This happens with respect to the surrounding anatomical structures, always including the possibility of adjusting both the direction and the position of the used osteosynthesis material. By using the proposed software, surgeons are able to pre-plan the out coming implant in its form and morphology with the aid of a computer-visualized model within a few minutes. Further, the resulting model can be stored in STL file format, the commonly used format for 3D printing. Using this technology, surgeons are able to print the virtual generated implant, or create an individually designed bending tool. This method leads to adapted osteosynthesis materials according to the surrounding anatomy and requires further a minimum amount of money and time.Comment: 19 pages, 13 Figures, 2 Table

Illustration of the baseline determination.

<p>The direction vector <i>D</i> (green) is set up parallel to the initial point's (red star) direction vector (green). The direction vector is perpendicular to the initial point's normal vector (purple). The origins of the cast rays (brown) are translated along the direction vector and checked for intersections.</p

Image of real patient x-ray data suffering from a mandibular angle fracture (left angle).

<p>Left image shows the untreated defect. The result of the treatment with applied miniplates after bone repositioning is shown on the right part of the figure.</p

Summary of results according to the trauma database due to facial injuries caused by ski accidents in Innsbruck (Department of Oral and Maxillofacial Surgery, Innsbruck, Austria).

<p>Summary of results according to the trauma database due to facial injuries caused by ski accidents in Innsbruck (Department of Oral and Maxillofacial Surgery, Innsbruck, Austria).</p

Results from the evaluation questionnaire for each subject using a six point Likert rating.

<p><i>Median</i> is the median value of the four subjects and <i>Error</i> describes the superimposed standard error. <i>Q11</i> is a <i>yes/no</i> question where <i>no</i> equals a value of <i>zero</i> and <i>yes</i> equals a value of <i>6</i>. The time <i>T</i> is measured in minutes.</p

Computer-aided position planning of miniplates to treat facial bone defects - Fig 12

<p>Example result containing all three available implants each located at a position where they generally are applied (left). For better illustration, the single implants are extended portrayed as well on the right side. The plate could easily be positioned according to the underlying bone contours by the used software module.</p

Bridge building principle with triangulation.

<p>Green crosses mark the corner of the ring element's plane side. To each baseline point (green points) a rectangle (light blue lines) is constructed. Rectangle triangulation, spanned by the two starting nodes (<i>N1</i> and <i>N2</i>) and two opposing nodes of the previous constructed rectangle (<i>N3</i> and <i>N4</i>). Node <i>N1</i>, <i>N3</i> and <i>N4</i> build a triangle <i>T2</i>, and Nodes <i>N1</i>, <i>N2</i> and <i>N3</i> build the second triangle <i>T1</i>.</p

Constructed network using the MeVisLab prototyping environment, including self-implemented modules named <i>CurvatureCalc</i> for baseline calculation and <i>ImplantGen</i> for generating the implant models.

<p>Constructed network using the MeVisLab prototyping environment, including self-implemented modules named <i>CurvatureCalc</i> for baseline calculation and <i>ImplantGen</i> for generating the implant models.</p

The patient's skull (white) with an applied baseline (green) are shown on the left side, where the normal vector <i>N</i> and the direction vector <i>D</i> are drawn for the placement of the ring elements.

<p>The ring element itself is shown in the right image, where the normal vector <i>N</i> and direction vector <i>D</i> (red), which have to be aligned with the vectors from the baseline, are illustrated.</p