Open-source navigation system for tracking dissociated parts with multi-registration.

PURPOSE: During reconstructive surgery, knee and hip replacements, and orthognathic surgery, small misalignments in the pose of prosthesis and bones can lead to severe complications. Hence, the translational and angular accuracies are critical. However, traditional image-based surgical navigation lacks orientation data between structures, and imageless systems are unsuitable for cases of deformed anatomy. We introduce an open-source navigation system using a multiple registration approach that can track instruments, implants, and bones to precisely guide the surgeon in emulating a preoperative plan. METHODS: We derived the analytical error of our method and designed a set of phantom experiments to measure its precision and accuracy. Additionally, we trained two classification models to predict the system reliability from fiducial points and surface matching registration data. Finally, to demonstrate the procedure feasibility, we conducted a complete workflow for a real clinical case of a patient with fibrous dysplasia and anatomical misalignment of the right femur using plastic bones. RESULTS: The system is able to track the dissociated fragments of the clinical case and average alignment errors in the anatomical phantoms of [Formula: see text]  mm and [Formula: see text]. While the fiducial-points registration showed satisfactory results given enough points and covered volume, we acknowledge that the surface refinement step is mandatory when attempting surface matching registrations. CONCLUSION: We believe that our device could bring significant advantages for the personalized treatment of complex surgical cases and that its multi-registration attribute is convenient for intraoperative registration loosening cases.

Computer-assisted surgery for replacement of the temporomandibular joint with customized prostheses: can we validate the results?

PURPOSE: Replacing the temporomandibular joint poses an important challenge to maxillofacial surgeons, and for certain disorders, it represents the treatment's gold standard. Computer-assisted surgery (comprising preoperative virtual planning, virtual intraoperative navigation and 3D printing) is a useful tool for this type of surgery. However, we do not know if and how much the final position of the prosthesis differs, in absolute values, from what was planned virtually in the preoperative phase. We propose a comparative result validation system for temporomandibular joint replacement METHODS: In the present study, we propose a comparative validation system using overlapping images, between the model obtained with preoperative virtual planning and the postoperative result. RESULTS: The mean difference for all screws of the glenoid prosthesis was 2.08 mm (range, 1.20-3.03) and for all screws of the condylar prosthesis it was 2.33 mm (range, 1.16-3.56). Mean overall difference between both prostheses in all patients was 2.21 mm (range, 1.16-3.56). CONCLUSIONS: The validation system proposed by overlapping pre- and postoperative images in temporomandibular joint replacement allowed us to establish differences in absolute values between the virtual preoperative model and the actual postoperative result expressed in millimeters.

Obtaining accurate and calibrated coil models for transcranial magnetic stimulation using magnetic field measurements.

Currently, simulations of the induced currents in the brain produced by transcranial magnetic stimulation (TMS) are used to elucidate the regions reached by stimuli. However, models commonly found in the literature are too general and neglect imperfections in the windings. Aiming to predict the stimulation sites in patients requires precise modeling of the electric field (E-field), and a proper calibration to adequate to the empirical data of the particular coil employed. Furthermore, most fabricators do not provide precise information about the coil geometries, and even using X-ray images may lead to subjective interpretations. We measured the three components of the vector magnetic field induced by a TMS figure-8 coil with spatial resolutions of up to 1 mm. Starting from a computerized tomography-based coil model, we applied a multivariate optimization algorithm to automatically modify the original model and obtain one that optimally fits the measurements. Differences between models were assessed in a human brain mesh using the finite-elements method showing up to 6% variations in the E-field magnitude. Our calibrated model could increase the precision of the estimated E-field induced in the brain during TMS, enhance the accuracy of delivered stimulation during functional brain mapping, and improve dosimetry for repetitive TMS. Graphical Abstract Geometrical model of TMS coil based on TAC images is optimally deformed to match magnetic field measurements. The calibrated model's induced electric field in the brain differs from the original.

In Vitro Comparative Study Between Conventional and Computer-Assisted Surgery Methods for Planning and Resection of Bone Sarcomas.

This poster aims to achieve an "in vitro" comparative study between three methods: 2D digital images planning and execution without navigation (freehand with ruler and caliper), 3D planning and execution without navigation (freehand with ruler and caliper) and 3D planning and execution guided with navigation. 3D planning and navigated procedures potentially improve sarcoma resection.

Oncologic and clinical outcomes in pelvic primary bone sarcomas treated with limb salvage surgery.

PURPOSE: We propose to study a group of patients with primary bone sarcoma of the pelvis treated with limb salvage surgery and analyze overall survival, local recurrence rates and functional outcomes. METHODS: A retrospective review was performed, and all patients diagnosed with pelvic primary bone sarcomas between 1990 and 2012 were analyzed. Patients treated with limb salvage surgery and with a minimum of 12-month follow-up for patients alive were included. The overall survival and the local recurrence rate were calculated for the assessment of oncological results. The associations with gender, age, histological grade, type of surgery, margins chemotherapy response and use of navigation were examined. RESULTS: Fifty-two patients were included in the study. The mean age was 37 years (range 10-82), and mean follow-up was 44 months (range 8-189). Forty-five (86 %) tumors were histologically classified as high-grade sarcomas, four (8 %) as low-grade sarcomas and three (6 %) as dedifferentiated sarcomas. Cancer-specific overall survival was 37.5 % for 5 years and 31 % for 10 years. Local recurrence rate was 30 %. High-grade tumors and chemotherapy necrosis below 90 % were negative prognosis factor. Postoperative complication rate was 34.5 % (n:18), being deep infection the most prevalent (n:13). Reconstruction of the pelvis after an oncology resection for primary pelvic sarcomas increased the incidence of complication significantly (p < 0.001). CONCLUSION: Primary bone sarcomas involving the pelvis are suggestive of a high-grade tumor and present poor oncologic outcomes. Pelvic reconstruction after a limb salvage surgery is associated with a high risk of complication. LEVEL OF EVIDENCE: Case series, Level IV.