Clinical Orthopaedics and Related Research®

, Volume 472, Issue 1, pp 238–247 | Cite as

The Effect of Geometric Variations in Posterior-stabilized Knee Designs on Motion Characteristics Measured in a Knee Loading Machine

  • Peter S. Walker
  • Michael T. Lowry
  • Anoop Kumar
Symposium: 2013 Knee Society Proceedings



In different posterior-stabilized (PS) total knees, there are considerable variations in condylar surface radii and cam-post geometry. To what extent these variations affect kinematics is not known. Furthermore, there are no clearly defined ideal kinematics for a total knee.


The purposes of this study were to determine (1) what the kinematic differences are caused by geometrical variations between PS total knee designs in use today; and (2) what design characteristics will produce kinematics that closely resemble that of the normal anatomic knee.


Four current PS designs with different geometries and one experimental asymmetric PS design, with a relatively conforming medial side, were tested in a purpose-built machine. The machine applied combinations of compressive, shear, and torque forces at a sequence of flexion angles to represent a range of everyday activities, consistent with the ASTM standard test for measuring constraint. The femorotibial contact points, the neutral path of motion, and the AP and internal-external laxities were used as the kinematic indicators.


The PS designs showed major differences in motion characteristics among themselves and with motion data from anatomic knees determined in a previous study. Abnormalities in the current designs included symmetric mediolateral motion, susceptibility to excessive AP medial laxity, and reduced laxity in high flexion. The asymmetric-guided motion design alleviated some but not all of the abnormalities.


Current PS designs showed kinematic abnormalities to a greater or lesser extent. An asymmetric design may provide a path to achieving a closer match to anatomic kinematics.

Clinical Relevance

One criterion for the evaluation of PS total knees is how closely the kinematics of the prosthesis resemble that of the anatomic knee, because this is likely to affect the quality of function.


Posterior Cruciate Ligament Flexion Angle Tibial Component Posterior Displacement Rotational Laxity 
These keywords were added by machine and not by the authors. This process is experimental and the keywords may be updated as the learning algorithm improves.



We thank Daniel Hennessy for constructing the desktop knee machine. Original design contributions to the machine were made by G. Yildirim. The finite element analysis study was carried out by B. Joshi with guidance from N. Gupta PhD, at NYU Polytechnic Institute.


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Copyright information

© The Association of Bone and Joint Surgeons® 2013

Authors and Affiliations

  • Peter S. Walker
    • 1
    • 2
    • 3
  • Michael T. Lowry
    • 1
  • Anoop Kumar
    • 2
  1. 1.Department of Orthopaedic SurgeryNew York University–Hospital for Joint DiseasesNew YorkUSA
  2. 2.Department of Mechanical and Aerospace EngineeringPolytechnic Institute of New York UniversityNew YorkUSA
  3. 3.Laboratory for Orthopaedic Implant DesignNew York University–Hospital for Joint DiseasesNew YorkUSA

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