title: Post-cam mechanics and tibiofemoral kinematics: a dynamic in vitro analysis of eight posterior-stabilized total knee designs.
abstract: OBJECTIVE
  Posterior cruciate ligament (PCL)-substituting total knee arthroplasty (TKA) designs were introduced to avoid paradoxical roll forward of the femur and to optimize knee kinematics. The aim of this in vitro study was to investigate post-cam function and contact mechanics and relate it to knee kinematics during squatting in eight contemporary posterior-stabilized TKA designs.
  
  
  METHODS
  All prostheses were fixed on custom-designed metal fixtures and mounted in a knee rig and five sequential-loaded squats were performed between 30° and 130° of flexion. Contact pressure and contact area were measured using pressure-sensitive Tekscan sensors on the posterior face of the post. Kinematics was recorded with reflective markers and infrared light-capturing cameras.
  
  
  RESULTS
  The post-cam mechanisms analyzed in this study are very variable in terms of design features. This leads to large variations in terms of the flexion angle at which the post and cam engage maximal contact force, contact pressure and contact area. We found that more functional post-cam mechanisms, which engage at lower flexion angle and have a similar behavior as normal PCL function, generally show more normal rollback and tibial rotation at the expense of higher contact forces and pressures. All designs show high contact forces. A positive correlation was found between contact force and initial contact angle.
  
  
  CONCLUSIONS
  Post-cam contact mechanics and kinematics were documented in a standardized setting. Post-cam contact mechanics are correlated with post-cam function. Outcomes of this study can help to develop more functional designs in future. Nevertheless, a compromise will always be made between functional requirements and risk of failure. We assume that more normal knee kinematics leads to more patient satisfaction because of better mobility. Understanding of the post-cam mechanism, and knowing how this system really works, is maybe the clue in further development of new total knee designs.
authors.affiliation: Orthopedie en Traumatologie, University Hospital Ghent, De Pintelaan 185, 9000, Ghent, Belgium. nelearnout@yahoo.com.
authors.forename: N
authors.initials: N
authors.lastname: Arnout
authors.affiliation: University Hospitals Leuven, Weligerveld 1, 3012, Ghent, Belgium.
authors.forename: L
authors.initials: L
authors.lastname: Vanlommel
authors.affiliation: University Hospitals Leuven, Weligerveld 1, 3012, Ghent, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Vanlommel
authors.affiliation: European Centre for Knee Research, Technologielaan, Heverlee, Belgium.
authors.forename: J P
authors.initials: JP
authors.lastname: Luyckx
authors.affiliation: European Centre for Knee Research, Technologielaan, Heverlee, Belgium.|Department of Mechanical Engineering, Biomechanics Section, Catholic University of Leuven, Louvain, Belgium.
authors.forename: L
authors.initials: L
authors.lastname: Labey
authors.affiliation: European Centre for Knee Research, Technologielaan, Heverlee, Belgium.|BEAMS Department, École Polytechnique de Bruxelles, Université Libre de Bruxelles, Brussels, Belgium.
authors.forename: B
authors.initials: B
authors.lastname: Innocenti
authors.affiliation: Orthopedie en Traumatologie, University Hospital Ghent, De Pintelaan 185, 9000, Ghent, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Victor
authors.affiliation: University Hospitals Leuven, Weligerveld 1, 3012, Ghent, Belgium.|ZOL, Genk, Belgium.
authors.forename: J
authors.initials: J
authors.lastname: Bellemans
mesh_terms: D019645:Arthroplasty, Replacement, Knee; D001696:Biomechanical Phenomena; D005269:Femur / Q000503:physiopathology* / Q000601:surgery; D006801:Humans; D007719:Knee Joint / Q000503:physiopathology* / Q000601:surgery; D007720:Knee Prosthesis; D008953:Models, Anatomic; D016119:Posterior Cruciate Ligament / Q000601:surgery*; D011187:Posture; D011474:Prosthesis Design; D016059:Range of Motion, Articular; D012399:Rotation; D013314:Stress, Mechanical; D013977:Tibia / Q000503:physiopathology* / Q000601:surgery
keywords: In vitro study; Kinematics; Post-cam failure; Posterior-stabilized TKA