title: Inadequacy of computed tomography for pre-operative planning of patellofemoral arthroplasty.
abstract: OBJECTIVE
  To evaluate the accuracy of preoperative planning for patellofemoral arthroplasty (PFA) by comparing: (1) virtual implant positioning simulated on pre-operative images versus (2) real implant positioning from post-operative images.
  
  
  METHODS
  The authors prospectively studied 15 patients that received a PFJ implant (Tornier, Montbonnot France). A pre-operative planning software was established to determine the size and position of the trochlear component. Pre-operative scans were used to perform virtual implantations by two different operators, which were then compared to the post-operative scans to calculate errors (ε) in implant positioning and intra-class correlation coefficients (ICC) for intra- and inter-observer repeatability.
  
  
  RESULTS
  Analysis was performed for 13 patients, for whom agreement between virtual and real surgery was excellent for anteroposterior (AP) position (ICC = 0.84; εmax= 3.5 mm), fair for proximodistal (PD) position (ICC = 0.50; εmax= 9.5 mm), and poor for mediolateral (ML) position (ICC = 0.07; εmax= 9.0 mm). It was fair for flexum-recurvatum (FR) alignment (ICC = 0.53; εmax= 8.2°), poor for varus-valgus (VV) alignment (ICC = 0.34; εmax= 10.0°), and internal-external (IE) rotation (ICC = 0.34; εmax= 10.6°).
  
  
  CONCLUSIONS
  Pre-operative planning was insufficiently accurate to follow intra-operatively, the greatest errors being angular alignment (VV and FR). The clinical relevance of these findings is that PFA is difficult to plan pre/operatively due to non-visibility of cartilage on CT scans and to trochlear dysplasia in most cases.
  
  
  METHODS
  Prospective evaluation of operative tools on consecutive patients, Level III.
authors.affiliation: ReSurg SA, 35 ch. de la Vuarpillière, 1260, Nyon, Switzerland. journals@resurg.eu.
authors.forename: Mo
authors.initials: M
authors.lastname: Saffarini
authors.affiliation: Department of Mechanical and Mechatronic Engineering Stellenbosch University, Private Bag X1, Matieland, 7600, Stellenbosch, South Africa.
authors.forename: Jacobus H
authors.initials: JH
authors.lastname: Müller
authors.affiliation: Lyon-Ortho-Clinic, Clinique de la Sauvegarde, 8 Avenue Ben Gourion, 69009, Lyon, France.
authors.forename: Giuseppe
authors.initials: G
authors.lastname: La Barbera
authors.affiliation: Orthopaedic Research Laboratory, Radboud University Medical Center, PO Box 9101, 6500HB, Nijmegen, The Netherlands.
authors.forename: Gerjon
authors.initials: G
authors.lastname: Hannink
authors.affiliation: Department of Mechanical and Mechatronic Engineering Stellenbosch University, Private Bag X1, Matieland, 7600, Stellenbosch, South Africa.
authors.forename: Kyung Jin
authors.initials: KJ
authors.lastname: Cho
authors.affiliation: Lyon-Ortho-Clinic, Clinique de la Sauvegarde, 8 Avenue Ben Gourion, 69009, Lyon, France.
authors.forename: Cécile
authors.initials: C
authors.lastname: Toanen
authors.affiliation: Lyon-Ortho-Clinic, Clinique de la Sauvegarde, 8 Avenue Ben Gourion, 69009, Lyon, France.
authors.forename: David
authors.initials: D
authors.lastname: Dejour
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D005602:France; D006801:Humans; D008297:Male; D008875:Middle Aged; D057071:Patellofemoral Joint / Q000601:surgery*; D010934:Planning Techniques; D057234:Preoperative Period; D011446:Prospective Studies; D014057:Tomography, X-Ray Computed
keywords: Patellofemoral arthritis; Patellofemoral arthroplasty; Preoperative planning; Trochlear dysplasia