title: Patellofemoral pressure after TKA in vitro: highly conforming vs. posterior stabilized inlays.
abstract: BACKGROUND
  When highly conforming polyethylene inlays were introduced into total knee arthroplasty (TKA), they were characterized as adding anteroposterior stability to the reconstructed knee. The aim of this study was to examine the patellofemoral pressure with the designs of a highly conforming and a posterior stabilized inlay. The patellofemoral pressure depends among other factors on the anteroposterior stability of the knee joint.
  
  
  METHODS
  Eight fresh frozen human knee specimens underwent testing in a kinematic device. Knee motion was driven by a hydraulic cylinder at an extension moment of 31 Nm. The patellofemoral contact pressure was measured using a pressure sensitive film (Tekscan((R)), Inc., Boston, USA). First, this was assessed after implantation of a cruciate retaining (CR) TKA with a highly conforming polyethylene insert before and after resection of the posterior cruciate ligament. After that, the same measurements were performed with a similar posterior stabilized prosthesis.
  
  
  RESULTS
  Patellofemoral contact pressures in the CR prosthesis using the highly conforming inlay were not significantly different before and after resection of the posterior cruciate ligament. However, after implantation of a posterior stabilized prosthesis peak pressure was significantly lower [Mean: 6.12, (SD 2.37) MPa] in comparison to the highly conforming type [7.12, (SD 2.53) MPa, P < 0.01] at a preserved posterior cruciate ligament. Further to that, the mean contact pressure turned out to be lower with the posterior stabilized design (P < 0.006).
  
  
  CONCLUSIONS
  The results of this study suggest that a posterior stabilized prosthesis design reduces the patellofemoral peak and mean pressure in comparison with a high conforming design. The better reproducible femoral rollback with a posterior stabilized model at a tibial ventral shift could serve as a possible explanation.
authors: Department of Orthopedics and Rheumatology, University Hospital Marburg, Baldingerstrasse, 35043, Marburg, Germany. heyse@med.uni-marburg.de
authors: Thomas Jan
authors: TJ
authors: Heyse
authors: Christoph
authors: C
authors: Becher
authors: Nadine
authors: N
authors: Kron
authors: Sven
authors: S
authors: Ostermeier
authors: Christof
authors: C
authors: Hurschler
authors: Markus D
authors: MD
authors: Schofer
authors: Carsten O
authors: CO
authors: Tibesku
authors: Susanne
authors: S
authors: Fuchs-Winkelmann
mesh_terms: D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee / Q000295:instrumentation*; D001696:Biomechanical Phenomena; D002102:Cadaver; D005260:Female; D005269:Femur / Q000503:physiopathology*; D006801:Humans; D007593:Joint Instability / Q000503:physiopathology*; D007719:Knee Joint / Q000503:physiopathology*; D007720:Knee Prosthesis; D008297:Male; D016896:Treatment Outcome