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In total hip arthroplasty, an optimal cup orientation is essential to avoid dislocations. Computer assisted systems provide the surgeon with the intra-operative cup orientation. However, these systems rely on the palpation of the anterior pelvic plane, and are thereby prone to the palpation error of this plane. As this error is directly linked to the soft tissue overlying the pelvic landmarks, we developed a navigated ultrasound system to acquire the anterior pelvic plane. 5 operators acquired 5 times the anterior pelvic plane of 2 female cadavers. After a learning curve, the acquisition of the plane took approximately 90 seconds. Compared to the anterior pelvic plane measured on the CT-scan, the mean rotation error was less than 0.5°, with a standard deviation of less than 1.2°. The mean version error was -1.2°, and the standard deviation remained below 1.9°. Our results confirm that navigated ultrasound is a very accurate tool to acquire the anterior pelvic plane and thereby allow an accurate navigation of total hip arthroplasty.

Objectives : This paper presents a new simulator for maxillo-facial surgery, that gathers the dental and the maxillo-facial analyses together into a single computer-assisted procedure. The idea is first to propose a repositioning of the maxilla, via the introduction of a 3D cephalometry, applied to a 3D virtual model of the patient's skull. Then, orthodontic data are integrated into this model, thanks to optical measurements of teeth plaster casts. Materials and Methods : The feasibility of the maxillo-facial demonstrator was first evaluated on a dry skull. To simulate malformations (and thus to simulate a "real" patient), the skull was modified and manually cut by the surgeon, in order to generate a given maxillo-facial malformation (with asymmetries in the sagittal, frontal and axial planes). Results : The validation of our simulator consisted in evaluating its ability to propose a bone repositioning diagnosis that will put the skull as it was in its original configuration. A first qualitative validation is provided in this paper, with a 1.5-mm error in the repositioning diagnosis. Conclusions : These results mainly validate the concept of a maxillo-facial numerical simulator that integrates 3D cephalometry and guarantees a correct dental occlusion.

This paper presents a surgical simulator for orthognathic surgery based on the integration of dental models and 3D cephalometry. The objective of dental models integration is to make coherent informations gathered from different sources (occlusal analysis and CT scan), and for that purpose, a system using a 3D optical localizer is used. The 3D Cephalometry analysis is used for the detection of dysmorphosis and surgical planning. This cephalometry integrates the Inferrence process for improving the surgical system. Both elements of our simulator have been implemented and technically validated with success.

A trend in total hip arthroplasty surgery has been to design more bone-preserving procedures, especially for younger patients. This study investigated the final implant positioning of a short metaphyseal femoral neck type of implant to determine whether leg length, caput collum diaphysis (CCD) angle, and offset could be re-created with different levels of femoral neck resection. Ten cadaveric hips in 6 whole-body specimens were used, with 3 fiducial markers to allow registration of computer navigation points to computed tomography scan data. Three femoral neck resection levels were investigated: 0 mm, +5 mm (the recommended level of resection), and +10 mm from the base of the femoral neck. Results showed that the CCD angle was significantly higher with 0-mm neck cut and the offset was lower, whereas the highest neck cut had longer leg-length results. Surgeons who use a short metaphyseal stem need to realize the importance of a proper femoral neck cut to restore anatomic parameters as well as the possible benefit of computer-assisted surgery to restore these anatomic parameters during surgery.