[Original developments of navigation techniques in traumatology]. / Développements originaux des techniques de navigation en traumatologie.

This article presents an original method for long objects modeling and two navigation applications in trauma surgery. Both concern long bone fracture treatment. Our modeling method requires only two x-ray views. The projection cones of the object are determined and their intersection is computed, providing an approached 30 model, which can be improved by adding a priori knowledge or other information. The first application concerns the control of diaphyseal fracture reduction treated by external fixation. Reference frames are fixed to the bone fragments and tracked by a 3D optical localizer, allowing the computation of their relative position. Approached 3D models of the fragments are displayed in real time according to the manipulation effected by the surgeon. The principal axes of the fragments, very useful for the fracture reduction, are also displayed. The alignment of the bone fragments is quantified by parameters provided in real time during the reduction. The second application concerns the distal locking of intra-medullary nails. A 3D model of the nail and its locking holes is built from two calibrated fluoroscopic views. The nail and the surgical tool are tracked thanks to reference frames fixed to each of them. A 3D view of these two elements is displayed in real time, guiding the surgeon in the difficult task of distal targeting. Experiments and results are presented for both applications. These techniques provide real 3D models to the surgeon during the operation, allowing precise guidance of the surgical gesture and considerable reduction of the irradiation to the patient and the surgical team.

Structure, composition and mechanical relations to function in sea urchin spine.

Sea urchins have characteristic spines that fulfil critical functions. Several studies revealed marked spine internal heterogeneities at different structural levels despite the single-crystal character of the spines. Most of these studies did not speculate about the functional meaning of these heterogeneities. Spine heterogeneities were investigated in the sea urchin Paracentrotuslividus and their possible functional implications discussed. Spines mainly show two morphological parts: the base, made of a meshwork stereom, and the shaft, with longitudinal plain septa and a central core of meshwork stereom. Electron Backscatter Diffraction showed no difference in crystallite orientation between the two structures. Atomic Absorption Spectrometry and Energy dispersive X-ray analysis revealed that Mg was not uniformly distributed in the spine. Mg concentration is higher in the inner part of the septa than in the septum outer part. Furthermore, a cyclic pattern of Mg concentration in septa was observed. This is suggested to be linked to the spine ontogeny. Nano- and microindentation analyses revealed that the septa have higher stiffness and hardness than the meshwork stereom and that septum stiffness and hardness present different trends in longitudinal and transverse section. These mechanical heterogeneities may have an adaptive functional value.

Conception of a navigation system controlling diaphyseal fracture reduction treated with external fixation.

BACKGROUND: The reduction of long bone fractures treated with external fixation is usually performed with fluoroscopic images, which include several disadvantages: 2D information, distortions, and irradiation to the patient and the surgical team. This article presents a new navigation technique to control the reduction of such fractures while minimizing the irradiation. METHODS: Optically tracked markers are fixed to pins inserted into the bone fragments. These last are modelled using two initial calibrated radiographs. The models can be improved with several types of anatomical data and are displayed in real time. RESULTS: This navigation system was tested on dry bones and an anatomical specimen leg. CONCLUSIONS: This new technique allows the visualization of the fracture in real time and from any viewpoint during the reduction. Irradiation is minimized using only two X-ray images.