, Volume 472, Issue 1, pp 254-262
Date: 29 Aug 2013

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

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Topic
Knee

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.

One of the authors (RDK) certifies that he or a member of his immediate family has or may receive payments or benefits during this study period of an amount of USD 100,001 to USD 1,000,000 from DePuy Synthese Inc (Warsaw, IN, USA). One of the authors (FL) certifies that he or a member of his immediate family has or may receive payments or benefits during this study period of an amount of USD 10,001 to USD 100,000 from DePuy Synthese Inc. One of the authors (DAD) certifies that he or a member of his immediate family has or may receive payments or benefits during this study period of an amount of more than USD 100,001 from DePuy Synthese Inc.
All ICMJE Conflict of Interest Forms for authors and Clinical Orthopaedics and Related Research editors and board members are on file with the publication and can be viewed on request.
Clinical Orthopaedics and Related Research neither advocates nor endorses the use of any treatment, drug, or device. Readers are encouraged to always seek additional information, including FDA-approval status, of any drug or device prior to clinical use.
Each author certifies that his or her institution approved the human protocols for these previous studies, that all investigations were conducted in conformity with ethical principles of research, and that informed consent for participation was also obtained.
This work was performed at the University of Tennessee, Knoxville, TN, USA.