title: Accuracy of linear drilling in temporal bone using drill press system for minimally invasive cochlear implantation.
abstract: OBJECTIVE
  A minimally invasive approach for cochlear implantation involves drilling a narrow linear path through the temporal bone from the skull surface directly to the cochlea for insertion of the electrode array without the need for an invasive mastoidectomy. Potential drill positioning errors must be accounted for to predict the effectiveness and safety of the procedure. The drilling accuracy of a system used for this procedure was evaluated in bone surrogate material under a range of clinically relevant parameters. Additional experiments were performed to isolate the error at various points along the path to better understand why deflections occur.
  
  
  METHODS
  An experimental setup to precisely position the drill press over a target was used. Custom bone surrogate test blocks were manufactured to resemble the mastoid region of the temporal bone. The drilling error was measured by creating divots in plastic sheets before and after drilling and using a microscope to localize the divots.
  
  
  RESULTS
  The drilling error was within the tolerance needed to avoid vital structures and ensure accurate placement of the electrode; however, some parameter sets yielded errors that may impact the effectiveness of the procedure when combined with other error sources. The error increases when the lateral stage of the path terminates in an air cell and when the guide bushings are positioned further from the skull surface. At contact points due to air cells along the trajectory, higher errors were found for impact angles of [Formula: see text] and higher as well as longer cantilevered drill lengths.
  
  
  CONCLUSIONS
  The results of these experiments can be used to define more accurate and safe drill trajectories for this minimally invasive surgical procedure.
authors.affiliation: Department of Mechanical Engineering, Vanderbilt University, 2400 Highland Ave., Olin Hall 101, Nashville, TN, 37212, USA. neal.p.dillon@vanderbilt.edu.
authors.forename: Neal P
authors.initials: NP
authors.lastname: Dillon
authors.affiliation: Department of Otolaryngology, Vanderbilt University Medical Center, Nashville, TN, USA.
authors.forename: Ramya
authors.initials: R
authors.lastname: Balachandran
authors.affiliation: Department of Otolaryngology, Vanderbilt University Medical Center, Nashville, TN, USA.
authors.forename: Robert F
authors.initials: RF
authors.lastname: Labadie
mesh_terms: D002102:Cadaver; D003051:Cochlea / Q000601:surgery*; D019929:Cochlear Implantation / Q000379:methods*; D006801:Humans; D007091:Image Processing, Computer-Assisted; D019060:Minimally Invasive Surgical Procedures / Q000379:methods; D056888:Patient Positioning; D025321:Surgery, Computer-Assisted / Q000379:methods; D013701:Temporal Bone / Q000601:surgery*
keywords: Cochlear implantation; Drilling accuracy; Minimally invasive surgery; Temporal bone