title: Patellar thickness and lateral retinacular release affects patellofemoral kinematics in total knee arthroplasty.
abstract: OBJECTIVE
  To study the effect of increasing patellar thickness (overstuffing) on patellofemoral kinematics in total knee arthroplasty and whether subsequent lateral retinacular release would restore the change in kinematics.
  
  
  METHODS
  The quadriceps of eight fresh-frozen knees were loaded on a custom-made jig. Kinematic data were recorded using an optical tracking device for the native knee, following total knee arthroplasty (TKA), then with patellar thicknesses from -2 to +4 mm, during knee extension motion. Staged lateral retinacular releases were performed to examine the restoration of normal patellar kinematics.
  
  
  RESULTS
  Compared to the native knee, TKA led to significant changes in patellofemoral kinematics, with significant increases in lateral shift, tilt and rotation. When patellar composite thickness was increased, the patella tilted further laterally. Lateral release partly corrected this lateral tilt but caused abnormal tibial external rotation. With complete release of the lateral retinaculum and capsule, the patella with an increased thickness of 4 mm remained more laterally tilted compared to the TKA with normal patellar thickness between 45° and 55° knee flexion and from 75° onwards. This was on average by 2.4° ± 2.9° (p < 0.05) and 2.°9 ± 3.0° (p < 0.01), respectively. Before the release, for those flexion ranges, the patella was tilted laterally by 4.7° ± 3.2° and 5.4° ± 2.7° more than in the TKA with matched patellar thickness.
  
  
  CONCLUSIONS
  Patellar thickness affects patellofemoral kinematics after TKA. Although lateral tilt was partly corrected by lateral retinacular release, this affected the tibiofemoral kinematics.
  
  
  METHODS
  IV.
authors.affiliation: Department of Orthopaedic Surgery, University of Malaya Medical Centre, Kuala Lumpur, Malaysia.
authors.forename: Azhar M
authors.initials: AM
authors.lastname: Merican
authors.forename: Kanishka M
authors.initials: KM
authors.lastname: Ghosh
authors.forename: Ferdinando Rodriguez Y
authors.initials: FR
authors.lastname: Baena
authors.forename: David J
authors.initials: DJ
authors.lastname: Deehan
authors.forename: Andrew A
authors.initials: AA
authors.lastname: Amis
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D001696:Biomechanical Phenomena; D006801:Humans; D008875:Middle Aged; D010329:Patella / Q000503:physiopathology / Q000601:surgery*; D057071:Patellofemoral Joint / Q000503:physiopathology* / Q000601:surgery; D046788:Patellofemoral Pain Syndrome / Q000209:etiology / Q000517:prevention & control; D016059:Range of Motion, Articular; D012399:Rotation