Clinical Orthopaedics and Related Research®

, Volume 472, Issue 1, pp 254–262

In Vivo Determination of Cam-Post Engagement in Fixed and Mobile-bearing TKA

  • Sumesh M. Zingde
  • Filip Leszko
  • Adrija Sharma
  • Mohamed R. Mahfouz
  • Richard D. Komistek
  • Douglas A. Dennis
Symposium: 2013 Knee Society Proceedings

DOI: 10.1007/s11999-013-3257-3

Cite this article as:
Zingde, S.M., Leszko, F., Sharma, A. et al. Clin Orthop Relat Res (2014) 472: 254. doi:10.1007/s11999-013-3257-3

Abstract

Background

Kinematics vary, sometimes in important ways, among the different types of total knee arthroplasty (TKA) designs, yet differences between the in vivo mechanisms of cam-post engagement in rotating-platform posterior-stabilized (PS) TKA, bicruciate-stabilized TKA, and fixed-bearing PS TKA designs remain largely uncharacterized.

Questions/purposes

The objective of this study was to determine the cam-post mechanism interaction for subjects implanted with three different TKA designs.

Methods

In vivo, analysis was conducted for patients implanted with nine rotating-platform PS TKAs, five knees with a fixed-bearing PS TKA, and 10 knees with a bicruciate-stabilized TKA while performing a deep knee bend. Three-dimensional kinematics of the implant components were determined by analysis of fluoroscopic images during flexion. The distances between the interacting surfaces were measured throughout flexion and instances and locations of contact were identified.

Results

Seven of the 10 bicruciate-stabilized knees analyzed had the femoral component engaged with the anterior aspect of the tibial post at full extension. Posterior cam-post engagement occurred at 34° for the bicruciate-stabilized (range, 17°–68°), 93° for the fixed-bearing PS (range, 88°–100°), and at 97° (range, 90°–104°) for rotating-platform PS TKA. In bicruciate-stabilized and fixed-bearing PS knees, the contact initially occurred on the medial aspect of the posterior surface of the tibial post and then moved centrally and superiorly with increasing flexion. For rotating-platform PS TKA, it was located centrally on the posterior surface of the post at all times.

Conclusions

This study suggests that mobility of the polyethylene might play an important role in ensuring central cam-post interaction in PS TKA. The polyethylene insert rotates axially in accordance with the rotating femur, maintaining central cam-post contact. This phenomenon was not observed in the fixed-bearing PS TKAs analyzed in this study.

Clinical Relevance

We speculate that this centralized symmetrical contact between the cam and posterior surface of the post could be beneficial clinically in terms of reducing wear of the posterior surface and particularly at the medial extremes of it.

Level of Evidence

Level III, therapeutic study. See Guidelines for Authors for a complete description of levels of evidence.

Copyright information

© The Association of Bone and Joint Surgeons® 2013

Authors and Affiliations

  • Sumesh M. Zingde
    • 1
  • Filip Leszko
    • 2
  • Adrija Sharma
    • 1
  • Mohamed R. Mahfouz
    • 1
  • Richard D. Komistek
    • 1
  • Douglas A. Dennis
    • 3
    • 4
    • 5
    • 6
  1. 1.Center for Musculoskeletal ResearchUniversity of TennesseeKnoxvilleUSA
  2. 2.DePuy Orthopaedics, IncWarsawUSA
  3. 3.Colorado Joint ReplacementDenverUSA
  4. 4.Department of Biomedical EngineeringUniversity of TennesseeKnoxvilleUSA
  5. 5.The University of Colorado Health Sciences CenterDenverUSA
  6. 6.Rocky Mountain Musculoskeletal Research LaboratoryDenverUSA