title: Posterior tibial slope accuracy with patient-specific cutting guides during total knee arthroplasty: A preliminary study of 50 cases.
abstract: BACKGROUND
  Patient-specific cutting guides were recently introduced to facilitate total knee arthroplasty (TKA). Their accuracy in achieving optimal implant alignment remains controversial. The objective of this study was to evaluate postoperative radiographic outcomes of 50 TKA procedures with special attention to posterior tibial slope (PTS), which is difficult to control intraoperatively. We hypothesized that patient-specific cutting guides failed to consistently produce the planned PTS.
  
  
  METHODS
  The Signature™ patient-specific cutting guides (Biomet) developed from magnetic resonance imaging data were used in a prospective case-series of 50 TKAs. The target PTS was 2°. Standardised digitised radiographs were obtained postoperatively and evaluated by an independent reader. Reproducibility of the radiographic measurements was assessed on 20 cases. The posterior cortical line of the proximal tibia was chosen as the reference for PTS measurement. Inaccuracy was defined as an at least 2° difference in either direction compared to the target.
  
  
  RESULTS
  The implant PTS was within 2° of the target in 72% of knees. In the remaining 28%, PTS was either excessive (n=10; maximum, 9°) or reversed (n=4; maximum, -6°). The postoperative hip-knee-ankle angle was 0° ± 3° in 88% of knees, and the greatest deviation was 9° of varus.
  
  
  CONCLUSIONS
  These findings support our hypothesis that patient-specific instrumentation decreases PTS accuracy. They are consistent with recently published data. In contrast, patient-specific instrumentation provided accurate alignment in the coronal plane.
authors.affiliation: Institut monégasque de médecine et chirurgie du sport, 98000 Monaco. Electronic address: schlattererb@im2s.mc.
authors.forename: B
authors.initials: B
authors.lastname: Schlatterer
authors.affiliation: Aix-Marseille université, CNRS, ISM UMR 7287, 13288 Marseille, France.
authors.forename: J-M
authors.initials: JM
authors.lastname: Linares
authors.affiliation: Institut monégasque de médecine et chirurgie du sport, 98000 Monaco.
authors.forename: J
authors.initials: J
authors.lastname: Cazal
authors.affiliation: Service de chirurgie orthopédique et traumatologie, hôpital A.-Michallon, CHU de Grenoble, 38043 Grenoble, France.
authors.forename: P
authors.initials: P
authors.lastname: Merloz
authors.affiliation: Service de chirurgie orthopédique et traumatologie du sport, hôpital sud, CHU de Grenoble, avenue de Kimberley, 38034 Échirolles, France.
authors.forename: S
authors.initials: S
authors.lastname: Plaweski
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000473:pathology / Q000601:surgery*; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000175:diagnosis / Q000601:surgery*; D011446:Prospective Studies; D015203:Reproducibility of Results; D013977:Tibia / Q000601:surgery*
keywords: Implant alignment; Patient-specific cutting guides; Posterior tibial slope; Specific instrumentation; Total knee arthroplasty