title: Detection of the center of the hip joint in computer-assisted surgery: an evaluation study of the Surgetics algorithm.
abstract: OBJECTIVE
  The aim of this paper is to assess the accuracy of an algorithm implemented by PRAXIM in the SURGETICS navigation station for detection of the hip center. This study will assess the robustness and accuracy of the algorithm in various clinical situations such as those involving non-sphericity of the femoral head, motion of the pelvis during hip center detection, and restricted range of motion.
  
  
  METHODS
  The localization of the hip center, based on kinematics, relies on the recording of n successive positions of the femoral rigid body in the localizer reference system during a passive circumduction motion of the hip joint. Therefore, the shape of the clouds of points acquired may vary from one acquisition to the next. To allow a comprehensive study of the consequences of these variations for hip center detection, we developed a simulator to generate numerous clouds of points. Results given subsequently for each test are the values of the difference between the femoral mechanical axis computed with C(c), the computed hip center, and the same axis computed with C(o), the reference hip center.
  
  
  RESULTS
  Test 1: Sensitivity to noise. The errors ranged from 3.33 E - 12 (SD 3.29E - 12) for a noise of 0 mm to 8.18E - 1 (SD - 7.05E - 1) for a noise of 15 mm. Test 2: Sensitivity to the shape of the acquisition motion. All trajectories gave an error < 1 degrees . Test 3: Sensitivity to restricted range of motion. No value > 1 degrees was found during this test. Test 4: Sensitivity to the distance between two points of the cloud. No value > 0.5 degrees was found during this test. Test 5: Sensitivity to the number of points included in the cloud. No value > 1 degrees was found during this test.
  
  
  CONCLUSIONS
  The Surgetics algorithm is robust to noise, can compensate for pelvic motion, and can be used even in the case of restricted range of motion.
authors.affiliation: Laboratoire de Traitement de l'Information Médicale, INSERM, ERIT-M 0102, Brest, France.
authors.forename: Eric
authors.initials: E
authors.lastname: Stindel
authors.forename: Daniel
authors.initials: D
authors.lastname: Gil
authors.forename: Jean-Louis
authors.initials: JL
authors.lastname: Briard
authors.forename: Philippe
authors.initials: P
authors.lastname: Merloz
authors.forename: Frédéric
authors.initials: F
authors.lastname: Dubrana
authors.forename: Christian
authors.initials: C
authors.lastname: Lefevre
mesh_terms: D000465:Algorithms; D001696:Biomechanical Phenomena; D006621:Hip Joint / Q000502:physiology* / Q000601:surgery*; D006801:Humans; D016059:Range of Motion, Articular; D012680:Sensitivity and Specificity; D025321:Surgery, Computer-Assisted / Q000295:instrumentation*