LiLouPen (Light Loup Pen)
View of the LiLouPen, designed to feed light from the environment into the optical waveguide. 
Visual field obtained clearly showing the implant and type of screw mechanism. The change of screw mechanism from a hexagon socket to StarDrive combined with minimally invasive techniques of implant removal place new demands on the surgeons and their instruments.
In order to remove the screws it is important to identify the size and the type of screw mechanism without having to expose the implant by surgical dissection.
The size of the screw can generally be identified radiologically with reference to the anatomical region, but the screw mechanism generally cannot.
The LilouPen has been designed to meet this need. It is the realization of a straightforward endoscopic procedure for the purpose of identifying the screw mechanism, freeing the screw head from ingrowing soft tissues, and positioning the screwdriver.
The pen is made from a transparent material, either glass or synthetics. Glass has the advantage that an optical reference (hologram) can be recorded. A synthetic material permits simple surface treatment in the sense of a Fresnel lens for light input. In a bright operative environment the image needs to be illuminated and displayed with as little dissipation as possible. The light for the illumination comes from sources in the environment (theater lights) or from a small LED attached to the pen.
A cylindrical retractor is used to expose the field of view, whereby the soft tissues between the end of the pen and the implant can be pushed away radially. The retractor consists of an expandable, cylindrical sleeve. The LilouPen is especially useful when the implants are covered by a thick, soft-tissue layer.
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