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Augmented reality guided condylectomy

  • Thijs Bussink
    Affiliations
    Radboudumc 3D lab, Radboud University Nijmegen Medical Centre, Geert Grooteplein 10, 6525 GA, Nijmegen, the Netherlands
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  • Thomas Maal
    Affiliations
    Radboudumc 3D lab, Radboud University Nijmegen Medical Centre, Geert Grooteplein 10, 6525 GA, Nijmegen, the Netherlands

    Department of Oral and Maxillofacial Surgery, Radboud University Nijmegen Medical Centre, Geert Grooteplein 10, 6525 GA, Nijmegen, the Netherlands
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  • Jene Meulstee
    Affiliations
    Radboudumc 3D lab, Radboud University Nijmegen Medical Centre, Geert Grooteplein 10, 6525 GA, Nijmegen, the Netherlands
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  • Tong Xi
    Correspondence
    Corresponding author at: Department of Oral and Maxillofacial Surgery, Radboud University Nijmegen Medical Centre, P.O. Box 9101, 6500 HB, Postal number 590, Nijmegen, the Netherlands.
    Affiliations
    Department of Oral and Maxillofacial Surgery, Radboud University Nijmegen Medical Centre, Geert Grooteplein 10, 6525 GA, Nijmegen, the Netherlands
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Open AccessPublished:January 31, 2022DOI:https://doi.org/10.1016/j.bjoms.2022.01.008

      Abstract

      An accurate transfer of a 3D virtual planned proportional condylectomy to the patient is challenging due to the limited surgical access. A new clinical workflow that uses augmented reality to assist a condylectomy is presented step-by-step. This AR-based approach has the potential to be implemented in the clinical setting routinely.

      Keywords

      Introduction

      Proportional condylectomy is increasingly being used as an initial treatment in unilateral condylar hyperplasia.
      • Fariña R.
      • Olate S.
      • Raposo A.
      • et al.
      High condylectomy versus proportional condylectomy: is secondary orthognathic surgery necessary?.
      The key in proportional condylectomy is able to place the osteotomy plane at the desired location to reduce the vertical ramal asymmetry. Clinically, it remains challenging to transfer a virtually planned condylectomy plane to the patient during surgery. The limited surgical access, the axial location of the condylar head, and the seating of condyle in the fossa often restricts a complete overview of the condylar head and hampers the use of surgical guides. The implementation of augmented reality (AR) can aid surgical interventions by presenting images of 3D virtual surgical planning on the operation field.
      • Kubben P.
      • Sinlae R.
      Feasibility of using a low-cost head-mounted augmented reality device in the operating room.
      We present a novel AR-guided work-flow for condylectomy.

      Material and methods

      A 38-year-old female presented at our department with a progressive chin point deviation to the right based on an unilateral condylar hyperplasia. A proportional condylectomy of the left condyle was proposed.
      A threshold-based segmentation in IPS CaseDesigner (KLS Martin Group) was used to create a 3D model of the mandible from an extended-height CBCT scan (FOV 16 × 22 cm; scanning time 2 × 20 s; voxel size, 0.4 mm; 3D Imaging System, Imaging Sciences International Inc). The osteotomy plane was virtually planned to resolve the discrepancy between the left and right ramal height.
      Surgery was performed under general anaesthesia with nasotracheal intubation. The left condyle was approached through a post-tragal incision with a limited superior preauricular extension. After gaining access to the condylar head, the surgeon identified the plane of condylectomy visually. Three marking points were place on the lateral condylar surface with a round bur.
      By wearing Microsoft Hololens2 (Microsoft), the position of three markings was checked using the following steps:
      • 1.
        A sterile quick response (QR) marker was attached to the lower dentition to allow tracking of the mandibular position through Hololens2.
      • 2.
        A stainless-steel pointer, equipped with a second QR marker, was used to check the location of the planned osteotomy line (Fig. 1).
        Figure thumbnail gr1
        Fig. 1The mandible was tracked by the QR marker fixated on the lower dentition (A). The position of the pointer with laser engraved QR-marker (B) was tracked by the HoloLens and the tip of the pointer (C) was visualized by the surgeon in the HoloLens. The surgical bur (D) was used to perform the condylectomy.
      • 3.
        An Unity-based inhouse-developed Hololens application, enabled the surgeon to visualise the planned position of the osteotomy line and the three markings. The HoloLens displayed a virtual arrow at the location of the pointer to direct the surgeon to move the pointer to the planned position (Fig. 2).
        Figure thumbnail gr2
        Fig. 2Visualisation in the HoloLens: the green arrow indicates how the tip of the pointer should be manipulated to target the planned osteotomy position. The red colour of the virtual arrow turned green in case the offset between the planned position of guidance points and the real-time position of the tip of the pointer was below 2 mm. The absolute distance between the pointer and the planned osteotomy point was indicated on the top left.
      Next, the actual condylectomy was performed with a round bur based on the markings. The cranial part of the condylar head was removed.
      Five days following surgery, a postoperative check-up CBCT was acquired. The planned and actual location of the condylectomy planes were compared.

      Results and discussion

      The 3D registration of planned and postoperative mandibular models (Fig. 3) showed that on the lateral, anterior and medial side of the condyle, the condylectomy was performed almost exactly as was planned (error ≤ 1 mm). However, the postoperative posterior border of the left condyle was located more caudally compared to the planning. This discrepancy could be a result of the fact that only the lateral position of the osteotomy was verified by HoloLens2.
      Figure thumbnail gr3
      Fig. 3Lateral view of the preoperative (light grey) and postoperative (dark grey) condyle with the planned (green) and the achieved (blue) osteotomy planes. The three points (red) were projected by the HoloLens and indicated the osteotomy plane. The posterior point was concordant with the planning and the middle point deviated by 1 mm.
      The accuracy of the presented method should be further investigated in future research. Besides, the software can be improved to make the AR application more intuitive. To eliminate the use of the pointer, the surgical handpiece (and thus the bur) can be equipped with a QR-code so that the position of the bur can be tracked and corrected throughout surgery. The magnitude of the registration error, perception error
      • Condino S.
      • Carbone M.
      • Piazza R.
      • Ferrari M.
      • Ferrari V.
      Perceptual limits of optical see-through visors for augmented reality guidance of manual tasks.
      and surgical error in AR-guided surgery should be investigated thoroughly.
      Although conventional surgical navigation systems can be used to guide to user during surgery, the combination of the Hololens with sterilisable QR markers is an easy and low-cost alternative. This AR solution allows the user to stay focused on the surgical field while attaining feedback from the planning. The surgeon is not forced to switch his/her view to an external monitor as in conventional navigation.
      • Meulstee J.W.
      • Nijsink J.
      • Schreurs R.
      • et al.
      Toward holographic-guided surgery.
      We believe that AR guidance is an adequate method to transfer a virtual planning for various CMF procedures. Especially during proportional condylectomy, where surgical guides are impractical, AR guidance is an effective method to assist the surgeon.

      Acknowledgement

      We would like to thank Gijs Luijten for designing and developing the QR marker and pointer. We thank Dylan Duits for his help during the development of the HoloLens application.

      Conflict of interest

      No.

      Ethics statement

      Ethics approval was obtained from the institutional ethics review board (#2019-5986). The ethics committee has passed a positive judgment on the study. Radboud University Nijmegen Medical Centre confirm the study doesn’t fall within the remit of the Medical Research Involving Human Subjects Act (WMO). Patients permission obtained.

      Sources of support

      None.

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