title: Control of paradoxical kinematics in posterior cruciate-retaining total knee arthroplasty by increasing posterior femoral offset.
abstract: OBJECTIVE
  Balancing the posterior cruciate ligament (PCL) with posterior cruciate-retaining total knee replacement (PCR-TKR) aims to restore femoral rollback. In practice, paradoxical roll forward persists. The purpose of this study is to propose a technique for optimizing PCL tension. Because PCL function starts above 60° of flexion, we hypothesize that PCL balancing requires flexion gap tightening by oversizing the femoral component and increasing posterior condylar offset (PCO).
  
  
  METHODS
  PCR-TKR was performed in 21 osteoarthritis patients with a gap-balancing technique. The femoral component was oversized if more than a 5-mm posterior drawer existed after tibial component implantation. Kinematics was recorded intra-operatively in two steps with dedicated navigation software (Praxim, La Tronche, Isère, France): antero-posterior (AP) displacements of condylo-tibial contact points were observed in native and implanted knees, with each knee serving as its own control. The absence of paradoxical displacements was verified once the final implants were inserted.
  
  
  RESULTS
  Paradoxical medial condyle displacement (11 mm) persisted in a single case. On average, posterior displacement of the medial condyle decreased from 9 ± 9 to 1 ± 6 mm (p = 0.001) and that of the lateral condyle from 16 ± 14 to 6 ± 6 mm (p = 0.006). In the 0°-30° flexion interval, posterior displacement was 2 times less than before implantation for the medial condyle (p = 0.001), and 4 times less for the lateral condyle (p = 0.004). The course of the lateral condyle decreased from 2 ± 3 to 0 ± 4 mm in the 90°-120° flexion interval (p = 0.046). Six-month flexion was 124° ± 17°.
  
  
  CONCLUSIONS
  Femoral component oversizing allows us to control paradoxical forward displacements in 95 % of cases. When balancing PCR prostheses, AP laxity should be taken into account. Increasing PCO appears to be a reliable technique for adjusting PCL balance. Thus, it may optimize extensor mechanism action and, subsequently, the functional results of PCR-TKR.
  
  
  METHODS
  Diagnostic study, Level II.
authors.affiliation: Department of Orthopaedic Surgery, Hôpitaux Universitaires Paris Nord Val de Seine, 46 rue Henri Huchard, 75877, Paris Cedex 18, France.
authors.forename: J
authors.initials: J
authors.lastname: Donadio
authors.forename: A
authors.initials: A
authors.lastname: Pelissier
authors.forename: P
authors.initials: P
authors.lastname: Boyer
authors.forename: P
authors.initials: P
authors.lastname: Massin
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D001696:Biomechanical Phenomena / Q000502:physiology; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007720:Knee Prosthesis; D008297:Male; D020370:Osteoarthritis, Knee / Q000601:surgery; D016119:Posterior Cruciate Ligament / Q000502:physiology*; D011446:Prospective Studies; D011474:Prosthesis Design; D017755:Prosthesis Fitting; D025321:Surgery, Computer-Assisted