Investigation of methods and materials for individually mouldable micro-stereotactic frame

• Applicants: Dr. Thomas Stephan Rau; Dr. Rolf Benedikt Salcher
• Subject Area: Otolaryngology, Phoniatrics and Audiology ; Mechanics
• Term: from 2019 to 2024
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 433571394

• Final Report Year: 2024

Final Report Abstract

Continuous advancements in surgery, with increasingly smaller access routes and ever-growing demands for precision, make the support of the surgeons through assistance systems indispensable. However, surgical robots are often large and expensive, or, like navigation systems, not sufficiently accurate. Some procedures also require only a simple positioning task, for which micro-stereotactic frames are suitable; these can be created directly in the operating room and used as instrument guides. This requires a fully sterile process characterized by intuitive and easily learned handling. In the project, fundamental research questions regarding the individual fabrication of an instrument guide were therefore explored, with a particular focus on accuracy and clinical handling. Another objective was to explore the limits of 'complexity reduction' in surgical assistance systems—while still maintaining the highest accuracy standards. In addition to bone cement, surgical tissue adhesives were identified and experimentally confirmed as a reliable option for the fabrication of customized drill guides from plastic semi-finished products. Unlike bone cement, this eliminates the approximately 15-minute curing time. Furthermore, by optimizing the material selection and geometry of the semi-finished products, the positioning accuracy was significantly improved from an initial 0.41 mm ± 0.27 mm to 0.08 mm ± 0.05 mm (maximum: 0.20 mm, n = 18). This experimentally demonstrated that custommoldable instrument guides represent a highly accurate yet cost-effective alternative to navigation and robotic systems. Another important project result is the development of a 'digitized' hexapod as an aid during the creation of the instrument guide. The adjustment of leg length still occurs manually, but the current length is detected and digitally displayed through integrated sensors. This has significantly increased the adjustment accuracy from (0.08 ± 0.20) mm to (0.01 ± 0.01) mm and reduced the largest individual error from 0.80 mm to 0.02 mm (n = 30). Such a digitized manufacturing system is therefore likely to represent an interesting economic alternative to expensive robotic systems without compromising patient safety. During the course of the project, the imoStar system was exemplarily adapted to various surgical procedures and experimentally tested on skull phantoms and human specimens: for minimally invasive access to a) the inner ear, b) the middle ear, c) the petrous apex, d) the internal auditory canal, as well as for neurosurgical target structures. Additionally, a prototype combining the system with a hydraulic insertion tool for automated cochlear implant electrode insertion was developed, demonstrating the versatility and adaptability of the basic principle.

Publications

• Anpassung eines modellierbaren Mini-Stereotaxiesystems an die Anforderungen neurochirurgischer Eingriffe. In Proc. 20th Annual Meeting of the German Society for Computer and Robot Assisted Surgery (CURAC) 2021, September 16-18, Düsseldorf, Germany
  Kilian J., Heuer J., Spindeldreier S., Lenarz T. & Rau T.S.
  
• Comparison in accuracy of using bone cement or superglue for fixation of components of a microstereotactic frame. Laryngo-Rhino-Otologie. Georg Thieme Verlag KG.
  Kilian, J.; Freiknecht, M.; Lenarz, T. & Rau, TS
  
• Concept description and accuracy evaluation of a moldable surgical targeting system. Journal of Medical Imaging, 8(01).
  Rau, Thomas S.; Witte, Sina; Uhlenbusch, Lea; Kahrs, Lüder A.; Lenarz, Thomas & Majdani, Omid
  
• Reducing the manual length setting error of a passive Gough-Stewart platform for surgical template fabrication using a digital measurement system. Current Directions in Biomedical Engineering, 7(2), 89-92.
  Kilian, Julia; Blum, Tobias; Laves, Max-Heinrich; Ortmaier, Tobias; Lenarz, Thomas & Rau, Thomas S.
  
• A minimally invasive, micro-stereotactic strategy for implantation of active middle ear implants. Laryngo-Rhino-Otologie, 101(S 02), S243-S244.
  Kilian, Julia; Engel, Thorben; Zuniga, M.Geraldine; Salcher, Rolf; Maier, Hannes; Artukarslan, Eralp; Lenarz, Thomas & Rau, ThomasS.
  
• Toward image-guided positioning of an automated insertion tool for cochlear implant electrodes. In Proc. 56th Annual Conference of the German Society for Biomedical Engineering (DGBMT within VDE), September 28-30, Innsbruck, Austria
  Rau T.S., Tzschoppe E., Cramer J., Kilian J., Lenarz T. & Zuniga M.G.
  
• A tailor-made micro-stereotactic system. In Proc. 30th Annual Meeting of the Society of Skull Base Surgery, October 11-14, Hannover, Germany
  Rau T.S. & Artukarslan E.N.
  
• Drilling accuracy evaluation of a mouldable surgical targeting system for minimally invasive access to anatomic targets in the temporal bone. European Archives of Oto-Rhino-Laryngology, 280(10), 4371-4379.
  Geiger, Lena; Zuniga, M. Geraldine; Lenarz, Thomas; Majdani, Omid & Rau, Thomas S.
  
• The planning and implementation of trajectories as approaches to the temporal bone via a mini stereo taxi system.. Laryngo-Rhino-Otologie, 102(S 02), S291-S291.
  Artukarslan, Eralp-Niyazi; Rau, Thomas; Lenarz, Thomas & Salcher, Rolf