RESUMO
PURPOSE: Mandibular reconstruction using fibula free flap is a challenging surgical procedure. To assist osteotomies, computer-assisted surgery (CAS) can be used. Nevertheless, precise registration is required and often necessitates anchored markers that disturb the patient and clinical flow. This work proposes a new contactless surface-based method adapted to featureless anatomies such as fibula to achieve a fast, precise, and reproducible registration. METHODS: Preoperatively, a CT-scan of the patient is realized and osteotomies are virtually planned. During surgery, a structured light camera digitizes the fibula. The obtained intraoperative point cloud is coarsely registered with the preoperative model using 3 points defined in the CT-scan and located on the patient's bone with a laser beam. Then, a fine registration is performed using an ICP algorithm. The registration accuracy was evaluated comparing the position of points engraved in a 3D-printed fibula with their position in the registered model and evaluating resulting osteotomies. Accuracy and execution time were compared to a conventional stylus-based registration method. The work was validated in vivo. RESULTS: The experiment performed on a 3D-printed model showed that execution time is equivalent to surface-based registration using a stylus, with a better accuracy (mean TRE of 0.9 mm vs 1.3 mm using stylus) and guarantee good osteotomies. The preliminary in vivo study proved the feasibility of the method. CONCLUSION: The proposed contactless surface-based registration method using structured light camera gave promising results in terms of accuracy and execution speed and should be useful to implement CAS for mandibular reconstruction.
RESUMO
PURPOSE: Fibula free flap is currently used in mandibular reconstruction. The main difficulties involved in this surgery concern mandible shaping and therefore, osteotomy positioning on the fibula. The use of navigation could help in osteotomy positioning, but accurate registration is required. We assess a surface-matching method for fibula registration that relies on an iterative closest point (ICP) algorithm. Since the fibula shape is landmark free, a robust registration initialization approach is used to avoid non-optimal local minimums in the ICP. METHODS: Bone surface-matching registration was evaluated on a 3D printed fibula and compared to its virtual reference model. The registration initialization relied on 3 initialization points placed on the surgically exposed area, geometrically remote from the fibular distal extremity. The bone surface was digitized, and the obtained point clouds were registered to the virtual reference model. The position of 3 assessment points engraved on the 3D printed fibula was then compared to that of the equivalent points on the virtual model. RESULTS: The registration procedure was performed 24 times by an expert surgeon. Seventy-two target registration errors (TRE) were computed, corresponding to the distance between the paired assessment points. Most TRE (86.1%) were less than 1 mm, with a maximum of 1.552 mm. The overall mean value was 0.759 ± 0.302 mm. CONCLUSION: This study illustrates a surface-matching approach for fibula registration, with an initialization method based on points remote from the fibula distal extremity. This registration technique gave promising results and should be considered as a valid registration method for straight bones like the fibula. These findings indicate that navigation can be used for fibula flap shaping for mandibular reconstruction, with a noninvasive and accurate registration method.