title: Functional joint line obliquity after kinematic total knee arthroplasty.
abstract: OBJECTIVE
  Kinematic total knee arthroplasty (TKA) is an emerging technique, but concerns remain around the effect of implanting the prosthesis in more anatomic orientations. Native knees show variation in joint line orientation relative to the tibial mechanical axis but the joint line remains parallel to the floor when standing. This study was undertaken to evaluate joint line obliquity relative to the floor when weight-bearing after kinematic TKA to see if a similar effect occurs.
  
  
  METHODS
  Preoperative and postoperative measurements were taken for 55 consecutive kinematically aligned TKAs, including the joint line orientation angle (JLOA), formed between the joint line and a line parallel to the floor.
  
  
  RESULTS
  The mean medial proximal tibial angle (MPTA) was 3.4° varus pre-operatively (1.7° valgus to 7.9° varus, SD 2.0), and 3.0° varus postoperatively (5.5° valgus to 6.5° varus, SD 2.1). The mean postoperative JLOA was 1.0° varus with a smaller range than the MPTA (2.6° valgus to 6° varus, SD 1.9). The difference between these two measurements was significant (mean 2°, SD 2.5, p < 0.001).
  
  
  CONCLUSIONS
  Relative to the mechanical axis, 33 tibial components would be considered at risk outliers, being orientated at more than 3° in varus or valgus. However, only six components were outside this range relative to the vertical, all in varus (mean 4.2°). This latter measurement may better represent how the prosthesis is functionally loaded and is similar to mechanically aligned TKAs with good survivorship. This may help explain why kinematic alignment does not lead to higher earlier failure rates that may result if similar orientations were seen with mechanically aligned TKA.
authors: Department of Surgery, Hôpital Maisonneuve-Rosemont, Université de Montréal, 5415 Boulevard de l'Assomption, Montréal, QC, H1T 2M, Canada.
authors: Jonathan
authors: J
authors: Hutt
authors: Department of Surgery, Hôpital Maisonneuve-Rosemont, Université de Montréal, 5415 Boulevard de l'Assomption, Montréal, QC, H1T 2M, Canada.
authors: Vincent
authors: V
authors: Massé
authors: Department of Surgery, Hôpital Maisonneuve-Rosemont, Université de Montréal, 5415 Boulevard de l'Assomption, Montréal, QC, H1T 2M, Canada.
authors: Martin
authors: M
authors: Lavigne
authors: Department of Surgery, Hôpital Maisonneuve-Rosemont, Université de Montréal, 5415 Boulevard de l'Assomption, Montréal, QC, H1T 2M, Canada. pa.vendittoli@me.com.
authors: Pascal-André
authors: PA
authors: Vendittoli
mesh_terms: D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D001696:Biomechanical Phenomena; D006801:Humans; D007719:Knee Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D011184:Postoperative Period; D011859:Radiography; D016474:Weight-Bearing
keywords: Alignment; Kinematic; Orientation; TKA