title: Temporal bone borehole accuracy for cochlear implantation influenced by drilling strategy: an in vitro study.
abstract: OBJECTIVE
  Minimally invasive cochlear implantation is a surgical technique which requires drilling a canal from the mastoid surface toward the basal turn of the cochlea. The choice of an appropriate drilling strategy is hypothesized to have significant influence on the achievable targeting accuracy. Therefore, a method is presented to analyze the contribution of the drilling process and drilling tool to the targeting error isolated from other error sources.
  
  
  METHODS
  The experimental setup to evaluate the borehole accuracy comprises a drill handpiece attached to a linear slide as well as a highly accurate coordinate measuring machine (CMM). Based on the specific requirements of the minimally invasive cochlear access, three drilling strategies, mainly characterized by different drill tools, are derived. The strategies are evaluated by drilling into synthetic temporal bone substitutes containing air-filled cavities to simulate mastoid cells. Deviations from the desired drill trajectories are determined based on measurements using the CMM.
  
  
  RESULTS
  Using the experimental setup, a total of 144 holes were drilled for accuracy evaluation. Errors resulting from the drilling process depend on the specific geometry of the tool as well as the angle at which the drill contacts the bone surface. Furthermore, there is a risk of the drill bit deflecting due to synthetic mastoid cells.
  
  
  CONCLUSIONS
  A single-flute gun drill combined with a pilot drill of the same diameter provided the best results for simulated minimally invasive cochlear implantation, based on an experimental method that may be used for testing further drilling process improvements.
authors.affiliation: Institute of Mechatronic Systems, Leibniz Universität Hannover, 30167 , Hannover, Germany. jan-philipp.kobler@imes.uni-hannover.de.
authors.forename: Jan-Philipp
authors.initials: JP
authors.lastname: Kobler
authors.affiliation: Institute of Mechatronic Systems, Leibniz Universität Hannover, 30167 , Hannover, Germany.
authors.forename: Michael
authors.initials: M
authors.lastname: Schoppe
authors.affiliation: Hannover Medical School, 30625 , Hannover, Germany.
authors.forename: G Jakob
authors.initials: GJ
authors.lastname: Lexow
authors.affiliation: Hannover Medical School, 30625 , Hannover, Germany.
authors.forename: Thomas S
authors.initials: TS
authors.lastname: Rau
authors.affiliation: Hannover Medical School, 30625 , Hannover, Germany.
authors.forename: Omid
authors.initials: O
authors.lastname: Majdani
authors.affiliation: Institute of Mechatronic Systems, Leibniz Universität Hannover, 30167 , Hannover, Germany.
authors.forename: Lüder A
authors.initials: LA
authors.lastname: Kahrs
authors.affiliation: Institute of Mechatronic Systems, Leibniz Universität Hannover, 30167 , Hannover, Germany.
authors.forename: Tobias
authors.initials: T
authors.lastname: Ortmaier
mesh_terms: D019929:Cochlear Implantation / Q000379:methods*; D006801:Humans; D066298:In Vitro Techniques; D065287:Robotic Surgical Procedures / Q000295:instrumentation*; D013701:Temporal Bone / Q000601:surgery*
keywords: Accuracy; Cochlear implants; Drill bit geometry; Drilling; Surgical robotics
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