title: In Vivo Three-Dimensional Patellar Mechanics: Normal Knees Compared with Domed and Anatomic Patellar Components.
abstract: BACKGROUND
  Patellofemoral complications are a major cause of revision surgery following total knee arthroplasty (TKA). High forces occurring at the patellofemoral articulation coupled with a small patellofemoral contact area pose substantial design challenges. In this study, the three-dimensional (3D) in vivo mechanics of domed and anatomically shaped patellar components were compared with those of native patellae.
  
  
  METHODS
  Ten normal knees, 10 treated with an LCS-PS (low contact stress-posterior stabilized) TKA (anatomically shaped patellar component), and 10 treated with a PFC Sigma RP-PS (press-fit condylar Sigma rotating platform-posterior stabilized) TKA (domed patellar component) were analyzed under fluoroscopic surveillance while the patient performed a weight-bearing deep knee bend from full knee extension to maximum knee flexion. Relevant bone geometries were segmented out from computed tomography (CT) scans, and computer-assisted-design (CAD) models of the implanted components were obtained from the manufacturer. Three-dimensional patellofemoral kinematics were obtained using a 3D-to-2D registration process. Contact mechanics were calculated using a distance map between the articulating patellar and femoral surfaces.
  
  
  RESULTS
  Both patellar component designs exhibited good rotational kinematics and tracked well within the femoral trochlea when compared with the normal patella. The contact areas in the TKA groups peaked at 60° of knee flexion (mean and standard deviation, 201 ± 63.4 mm for the LCS-PS group and 218 ± 95.4 mm for the Sigma RP-PS group), and the areas were substantially smaller than those previously reported for the normal patella. Contact points in the TKA groups stayed close to the center of the patellar components.
  
  
  CONCLUSIONS
  Both designs performed satisfactorily, although patellofemoral contact areas were reduced in comparison with those in the native patella.
  
  
  METHODS
  Therapeutic Level III. See Instructions for Authors for a complete description of levels of evidence.
authors.affiliation: 1Center for Musculoskeletal Research, University of Tennessee, Knoxville, Tennessee 2Colorado Joint Replacement, Denver, Colorado 3Department of Bioengineering, University of Denver, Denver, Colorado 4University of Colorado School of Medicine, Denver, Colorado.
authors.forename: Adrija
authors.initials: A
authors.lastname: Sharma
authors.forename: Trevor F
authors.initials: TF
authors.lastname: Grieco
authors.forename: Sumesh M
authors.initials: SM
authors.lastname: Zingde
authors.forename: Douglas A
authors.initials: DA
authors.lastname: Dennis
authors.forename: Matthew R
authors.initials: MR
authors.lastname: Anderle
authors.forename: Richard D
authors.initials: RD
authors.lastname: Komistek
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000295:instrumentation* / Q000379:methods; D001696:Biomechanical Phenomena; D005260:Female; D006801:Humans; D007592:Joint Diseases / Q000601:surgery; D007719:Knee Joint / Q000502:physiology* / Q000503:physiopathology / Q000601:surgery; D007720:Knee Prosthesis; D008297:Male; D008875:Middle Aged; D010329:Patella / Q000502:physiology* / Q000601:surgery; D057071:Patellofemoral Joint / Q000502:physiology* / Q000503:physiopathology / Q000601:surgery; D011474:Prosthesis Design