title: Learning how to resurface cam-type femoral heads with acceptable accuracy and precision: the role of computed tomography-based navigation.
abstract: BACKGROUND
  Resurfacing arthroplasty for cam-type deformities, which are a common cause of early osteoarthritis, is a technically demanding operation. Like any other arthroplasty, it requires both accuracy and precision. On the basis of the results of series reported by expert surgeons, we considered it desirable that this operation should be performed within +/-10 degrees of the desired angular orientation and +/-6 mm of entry-point translation in 95% of hips. Technological aids are now available to help surgeons achieve that level of accuracy. Three models of cam-type hips of increasing severity were used to assess the efficacy of three systems of instrumentation at delivering the required level of accuracy and precision.
  
  
  METHODS
  Thirty-two students of surgical technology were instructed in hip resurfacing and shown detailed plans of the desired operative outcome for the three hips with cam-type deformity. They then used conventional instruments, imageless navigation, and computed tomography-based navigation to perform the operation as accurately as possible.
  
  
  RESULTS
  Conventional instrumentation produced an unacceptably wide range of entry-point errors. Imageless navigation was able to deliver adequate accuracy and precision in varus-valgus angulation and superoinferior translation, but was less satisfactory in version and anteroposterior translation. Computed tomography-based navigation enabled novice surgeons to navigate hips that had difficult cam-type deformity with acceptable precision in all four degrees of freedom measured.
  
  
  CONCLUSIONS
  Only computed tomography-based navigation appears to be appropriate for delivering both the accuracy and the precision needed by surgeons on the steep part of their learning curve. Neither conventional neck-based instrumentation nor imageless navigation provided enough help for novice surgeons learning to perform this technically challenging operation.
authors.affiliation: Department of Orthopaedics, Imperial College London, 5 Devonshire Place, London W1G 6HL, United Kingdom. j.cobb@imperial.ac.uk
authors.forename: Justin P
authors.initials: JP
authors.lastname: Cobb
authors.forename: Vijayaraj
authors.initials: V
authors.lastname: Kannan
authors.forename: Wael
authors.initials: W
authors.lastname: Dandachli
authors.forename: Farhad
authors.initials: F
authors.lastname: Iranpour
authors.forename: Klaus U
authors.initials: KU
authors.lastname: Brust
authors.forename: Alister J
authors.initials: AJ
authors.lastname: Hart
mesh_terms: D006621:Hip Joint / Q000000981:diagnostic imaging; D006622:Hip Prosthesis; D006801:Humans; D008953:Models, Anatomic; D009985:Orthopedics / Q000193:education; D015207:Osteoarthritis, Hip / Q000601:surgery; D019919:Prosthesis Implantation / Q000379:methods*; D014057:Tomography, X-Ray Computed; D016896:Treatment Outcome