title: Development of a biomechanical guidance system for periacetabular osteotomy.
abstract: OBJECTIVE
  This paper presents and validates a computer-navigated system for performing periacetabular osteotomy (PAO) to treat developmental dysplasia of the hip. The main motivation of the biomechanical guidance system (BGS) is to plan and track the osteotomy fragment in real time during PAO while simplifying the procedure for less-experienced surgeons. The BGS aims at developing a platform for comparing biomechanical states of the joint with the current gold standard geometric assessment of anatomical angles. The purpose of this study was to (1) determine the accuracy with which the BGS tracks the hip joint through repositioning and (2) identify improvements to the workflow.
  
  
  METHODS
  Nineteen cadaveric validation studies quantified system accuracy, verified system application, and helped to refine surgical protocol. In two surgeries, navigation and registration accuracy were computed by affixing fiducials to two cadavers prior to surgery. All scenarios compared anatomical angle measurements and joint positioning as measured intraoperatively to postoperatively.
  
  
  RESULTS
  In the two cases with fiducials, computed fragment transformations deviated from measured fiducial transformations by 1.4 and 1.8 mm in translation and 1.0° and 2.2° in rotation, respectively. The additional seventeen surgeries showed strong agreement between intraoperative and postoperative anatomical angles, helped to refine the surgical protocol, and demonstrated system robustness.
  
  
  CONCLUSIONS
  Estimated accuracy with BGS appeared acceptable for future surgical applications. Several major system requirements were identified and addressed, improving the BGS and making it feasible for clinical studies.
authors.affiliation: Research and Exploratory Development Department, Johns Hopkins University Applied Physics Laboratory, 11100 Johns Hopkins Rd, 21-S100, Laurel, MD, 20723, USA, Ryan.Murphy@jhuapl.edu.
authors.forename: Ryan J
authors.initials: RJ
authors.lastname: Murphy
authors.forename: Robert S
authors.initials: RS
authors.lastname: Armiger
authors.forename: Jyri
authors.initials: J
authors.lastname: Lepistö
authors.forename: Simon C
authors.initials: SC
authors.lastname: Mears
authors.forename: Russell H
authors.initials: RH
authors.lastname: Taylor
authors.forename: Mehran
authors.initials: M
authors.lastname: Armand
mesh_terms: D000077:Acetabulum / Q000601:surgery*; D006621:Hip Joint / Q000601:surgery*; D006801:Humans; D010027:Osteotomy / Q000295:instrumentation / Q000379:methods*; D025321:Surgery, Computer-Assisted