title: The effect of trochlea tilting on patellofemoral contact patterns after total knee arthroplasty: an in vitro study.
abstract: BACKGROUND
  Patellofemoral complications are one major concern after total knee arthroplasty (TKA). Anterior knee pain is one of these complications and to a high percentage responsible for unsatisfied patients after TKA. Malrotation of the femoral component can contribute to retropatellar peak pressure and consequently to anterior knee pain.
  
  
  METHODS
  Eight fresh frozen cadavers were tested in a force-controlled knee rig after TKA during isokinetic flexing of the knee from 20° to 120° under constant load. By tilting the trochlea in the material of the created femoral component replicas, a rotation of the femoral component by 3° internal, 0° (neutral), 3° and 6° external rotation to transepicondylar line was simulated without changing flexion or extension gap. Retropatellar pressure distribution was measured during flexion and extension of the knee while quadriceps muscles and hamstring forces were applied.
  
  
  RESULTS
  Maximum peak pressure for internal rotation of the trochlea was 7.32 ± 2.31 MPa, in neutral position the pressure reduced slightly to 7.31 ± 2.12 MPa and during further external rotation of trochlea rotation a decrease from 3° with 7.18 ± 2.14 MPa to 6° with 6.22 ± 1.83 MPa was observed (p < 0.01). There was a tendency of lower quadriceps force with increasing external rotation of the trochlea (p = 0.08).
  
  
  CONCLUSIONS
  The implantation of the femoral component by 3° internal trochlea rotation to transepicondylar line resulted in a highly significant increase of the mean maximal retropatellar pressure compared to 6° external rotation of the trochlea of the femoral component (p < 0.01). A higher retropatellar pressure might lead to anterior knee pain after TKA. We recommend an external rotation of the femoral component between 3° and 6° to anatomical transepicondylar line to reduce the maximal retropatellar pressure, but only if adequate soft tissue balancing and stable knee kinematics are provided.
authors: Department of Orthopedic Surgery, Physical Medicine and Rehabilitation, University Hospital of Munich (LMU), Campus Grosshadern, Marchioninistr. 15, 81377, Munich, Germany, arnd.steinbrueck@med.uni-muenchen.de.
authors: Arnd
authors: A
authors: Steinbrück
authors: Christian
authors: C
authors: Schröder
authors: Matthias
authors: M
authors: Woiczinski
authors: Andreas
authors: A
authors: Fottner
authors: Peter E
authors: PE
authors: Müller
authors: Volkmar
authors: V
authors: Jansson
mesh_terms: D000328:Adult; D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007719:Knee Joint / Q000502:physiology* / Q000601:surgery*; D008297:Male; D008875:Middle Aged; D052097:Quadriceps Muscle / Q000502:physiology; D016059:Range of Motion, Articular