title: Influence of post-cam design of posterior stabilized knee prosthesis on tibiofemoral motion during high knee flexion.
abstract: BACKGROUND
  The post-cam design of contemporary posterior stabilized knee prosthesis can be categorized into flat-on-flat or curve-on-curve contact surfaces. The curve-on-curve design has been demonstrated its advantage of reducing stress concentration when the knee sustained an anteroposterior force with tibial rotation. How the post-cam design affects knee kinematics is still unknown, particularly, to compare the difference between the two design features. Analyzing knee kinematics of posterior stabilized knee prosthesis with various post-cam designs should provide certain instructions to the modification of prosthesis design.
  
  
  METHODS
  A dynamic knee model was utilized to investigate tibiofemoral motion of various post-cam designs during high knee flexion. Two posterior stabilized knee models were constructed with flat-on-flat and curve-on-curve contact surfaces of post-cam. Dynamic data of axial tibial rotation and femoral translation were measured from full-extension to 135°.
  
  
  RESULTS
  Internal tibial rotation increased with knee flexion in both designs. Before post-cam engagement, the magnitude of internal tibial rotation was close in the two designs. However, tibial rotation angle decreased beyond femoral cam engaged with tibial post. The rate of reduction of tibial rotation was relatively lower in the curve-on-curve design. From post-cam engagement to extreme flexion, the curve-on-curve design had greater internal tibial rotation.
  
  
  CONCLUSIONS
  Motion constraint was generated by medial impingement of femoral cam on tibial post. It would interfere with the axial motion of the femur relative to the tibia, resulting in decrease of internal tibial rotation. Elimination of rotational constraint should be necessary for achieving better tibial rotation during high knee flexion.
authors.affiliation: Orthopaedic Biomechanics Laboratory, Institute of Biomedical Engineering, National Yang Ming University, Taipei, Taiwan.
authors.forename: Kun-Jhih
authors.initials: KJ
authors.lastname: Lin
authors.forename: Chang-Hung
authors.initials: CH
authors.lastname: Huang
authors.forename: Yu-Liang
authors.initials: YL
authors.lastname: Liu
authors.forename: Wen-Chuan
authors.initials: WC
authors.lastname: Chen
authors.forename: Tsung-Wei
authors.initials: TW
authors.lastname: Chang
authors.forename: Chan-Tsung
authors.initials: CT
authors.lastname: Yang
authors.forename: Yu-Shu
authors.initials: YS
authors.lastname: Lai
authors.forename: Cheng-Kung
authors.initials: CK
authors.lastname: Cheng
mesh_terms: D019645:Arthroplasty, Replacement, Knee / Q000379:methods; D001696:Biomechanical Phenomena; D005269:Femur / Q000033:anatomy & histology*; D006801:Humans; D007717:Knee / Q000033:anatomy & histology; D007719:Knee Joint / Q000601:surgery; D007720:Knee Prosthesis; D015233:Models, Statistical; D009038:Motion; D009068:Movement; D011474:Prosthesis Design / Q000379:methods*; D016059:Range of Motion, Articular; D012399:Rotation; D013977:Tibia / Q000033:anatomy & histology*