title: Less femorotibial rotation and AP translation in deep-dished total knee arthroplasty. An intraoperative kinematic study using navigation.
abstract: OBJECTIVE
  Hyper-congruent inserts have been proposed as another means of posterior stabilization in total knee arthroplasty. Their kinematics, partially unexplored, is reported to be possibly erratic. The objectives of the present study were to detect whether prostheses with such a constrained design would provide antero-posterior (AP) stability without interfering with high flexion.
  
  
  METHODS
  The kinematics of 10 knees replaced with hyper-congruent inserts was tested intra-operatively with a specially designed navigation system (Praxim, La Tronche, Isère, France), to measure AP displacements of femoro-tibial contact points at knee flexion.
  
  
  RESULTS
  Femoro-tibial contact points in full extension were in a posterior position compared to their initial position before implantation (8 ± 6 mm medially, 15 ± 10 mm laterally, P < 0.004). AP displacements were different from pre-operative displacements (3 ± 4 mm vs -5 ± 2 mm for the medial condyle, P < 0.01 and -2 ± 6 mm vs -22 ± 8 mm for the lateral condyle, P < 0.001). Forward rolling persisted in four cases, with the medial condyle being involved in three of them (9, 9, and 6 mm, respectively). Post-operative flexion of 122° on average was not correlated with AP displacements.
  
  
  CONCLUSIONS
  Hyper-congruent prostheses partially stabilized femoral condyles at knee flexion. Posterior displacements were reduced with no consequence on range of flexion. Posterior stabilization was imperfect, and paradoxical displacements were detected by navigation, which could therefore help optimize knee balance.
  
  
  METHODS
  Diagnostic study, Level II.
authors: Department of Orthopaedic Surgery, Bichat Claude Bernard Hospital, Paris Diderot University, 46 rue Henri Huchard, 75877 Paris cedex 18, France. philippe.massin@bch.aphp.fr
authors: Philippe
authors: P
authors: Massin
authors: Patrick
authors: P
authors: Boyer
authors: Marc
authors: M
authors: Sabourin
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology* / Q000601:surgery*; D007720:Knee Prosthesis; D008875:Middle Aged; D011474:Prosthesis Design; D016059:Range of Motion, Articular; D012399:Rotation; D013238:Stereotaxic Techniques