J Knee Surg 2010; 23(3): 153-162
DOI: 10.1055/s-0030-1268696
ORIGINAL ARTICLE

© Thieme Medical Publishers

Tibial Insert Micromotion of Various Total Knee Arthroplasty Devices

Safia Bhimji1 , Aiguo Wang1 , Thomas Schmalzried2
  • 1Stryker Orthopedics, Research and Development, Mahwah, New Jersey
  • 2Saint Vincent Medical Center, Los Angeles, California
Further Information

Publication History

Publication Date:
06 December 2010 (online)

ABSTRACT

The objective of this study was to develop a novel method to quantify rotational micromotion of modular tibial components that incorporates physiologic loading conditions, a physiologic test environment, and constraint characteristics of the articulating surface. The methodology is reviewed and data are presented on four total knee designs. Results showed the design with a rotational stabilizing island to demonstrate the most capability in resisting rotational micromotion for a given reacted torque, followed by a full peripheral capture device, then a partial peripheral capture device, and then a full peripheral capture device with a posterior lipped edge. Under walking and stair-climbing loads, the full peripheral capture device imparts more torque to the insert than the other designs due to the higher constraint of its articulating surface and thus experiences the most micromotion. The rotational stabilizing island device reveals the least amount of motion, due to a combination of its locking mechanism and a less constrained articular surface.

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APPENDIX A

In this study, micromotion was defined as the amount of rotation the insert undergoes within the plane of the baseplate as a result of torques applied at the articulating surface. To calculate this motion, a coordinate system was established on the insert with the x-axis corresponding with the A/P axis, the y-axis with the M/L axis, and the z-axis with the S/I axis (Fig. [A-1]). Insert rotation was calculated about the z-axis using the equations below and LVDT displacement data of the three spheres shown (AL, AM, and P):

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where AL y i P y i, AL z i, AM z i, P z i are initial positions of spheres AL, P, and AM along the y- and z-axes before testing is started; AL y i, P y i, AL z i, AM z i, P z i are positions of those spheres along the y- and z-axes at every time interval collected; and R α, R β, R γ are distances between the spheres as illustrated in Fig. [A-1].

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Figure A-1 Sphere locations and coordinate system definition.

Then,

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where φ z is defined as rotation of the insert within the plane of the baseplate.

Safia BhimjiM.S. 

Stryker Orthopedics–Research and Development

325 Corporate Drive, Mahwah, NJ 07430

Email: safia.bhimji@stryker.com

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