A Comparison of Wear Among Mobile and Fixed Bearing Knee Replacements

July 30, 2012 updated by: C. Anderson Engh, Jr., MD, Anderson Orthopaedic Research Institute

A Comparison of Volumetric Wear Among DePuy Mobile and Fixed Bearing Knee Tibial Inserts

The purpose of this study is to determine the amount of polyethylene wear associated with knee replacement designs that incorporate either a fixed or mobile bearing. Tibial polyethylene inserts retrieved from modular total knee replacements during revision operations will be analyzed by obtaining micro-CT images of the retrieved inserts. The components of total volumetric polyethylene loss, including wear associated with the medial articular, lateral articular and backside regions of the insert be quantified by comparing the worn insert with an unworn control. The investigators hypothesize that the fixed bearing inserts where the polyethylene is locked to the metal baseplate will demonstrate more volumetric wear than the mobile bearing inserts that are designed to slide or rotate on the metal baseplate.

Study Overview

Status

Completed

Conditions

Detailed Description

Polyethylene wear is a major factor limiting the longevity of total knee arthroplasty. Evaluation of the volumetric wear of explanted polyethylene tibial inserts can provide valuable insight into the performance of different designs. Current technologies available to measure the volumetric wear of tibial inserts include gravimetric techniques, coordinate measuring machines (CMM), laser-scanning, and micro-CT.

In this study, we will employ micro-CT to determine volumetric wear because it allows us to obtain high-resolution three-dimensional images of the entire insert volume, including the surfaces as well as the interior of the insert. The micro-CT images will be used to reconstruct the entire three-dimensional geometry of the insert (including subsurface voids) and we will use image analysis software to partition the reconstructed insert into discrete regions (i.e. medial/lateral articulating surfaces, backside, and post), allowing us to determine how various regions contribute to total implant wear. By subdividing the insert into discrete regions, our analysis techniques will also enable us to account for material removed from the insert during explantation when evaluating implant wear. By comparing retrieved inserts with unworn controls using three-dimensional image analysis software, we will also quantify plastic deformation by measuring the volume of material that has deformed outside the confines of the control insert. Additionally, inspection of shape differences between the worn and unworn specimens will enable us to distinguish between implant wear, plastic deformation and volume differences associated with manufacturing tolerances. Although partial voluming effects can make edge detection challenging, high resolution micro-CT images tend to minimize these effects and we will use gravimetric measurements to determine an insert-specific Hounsfield threshold that will be used to define the image volume for each specimen. We will subsequently validate the accuracy of the reconstructed insert volume derived from the micro-CT image by comparing it with linear measurements from the actual specimen at several discrete locations.

The use of micro-CT scans to evaluate the in vivo volumetric wear associated with different designs will enable accurate measurement of volumetric polyethylene loss from different regions of the insert. This information will provide a better understanding of the clinical outcome associated with different design strategies and provide data to guide future development efforts. We hypothesize that fixed bearing inserts, where the polyethylene is locked to the metal baseplate, will demonstrate more volumetric wear than the mobile bearing inserts that are designed to slide or rotate on the metal baseplate.

Articular side wear will be measured by registering micro-CT images from retrieved and control inserts on unworn portions of the articular surface using the Analyze image analysis software (Mayo Biomedical Imaging Resource, Rochester, MN). Differences in volume among the retrieved and unworn control inserts will be evaluated accounting for plastic deformation that may occur in vivo. Volumetric wear for the entire insert and subregions will be calculated by subtracting the volume of plastic deformation (corresponding to regions of the retrieved insert outside the boundaries of the control insert) from the volume of material lost within the confines of the original insert geometry. We will compare wear among the mobile and fixed bearings using an Independent Sample t-test or Mann-Whitney U, depending on the distribution of the data. We will also use multiple linear regression analysis to examine the relationship between insert wear and other variables, including time in vivo, terminal sterilization technique for the insert and patient-related factors such as gender, age, and body mass index (BMI).

Study Type

Observational

Enrollment (Actual)

24

Contacts and Locations

This section provides the contact details for those conducting the study, and information on where this study is being conducted.

Study Locations

    • Virginia
      • Alexandria, Virginia, United States, 22306
        • Anderson Orthopaedic Research Institute

Participation Criteria

Researchers look for people who fit a certain description, called eligibility criteria. Some examples of these criteria are a person's general health condition or prior treatments.

Eligibility Criteria

Ages Eligible for Study

18 years and older (Adult, Older Adult)

Accepts Healthy Volunteers

No

Genders Eligible for Study

All

Sampling Method

Non-Probability Sample

Study Population

Retrieved polyethylene tibial inserts archived as part the Anderson Orthopaedic Research Institute's implant retrieval program.

Description

Inclusion Criteria:

  • DePuy mobile and fixed bearing polyethylene tibial inserts retrieved after at least 12 months in vivo.
  • Inserts terminally sterilized by gas plasma or with gamma radiation in oxygen-free barrier packaging.

Exclusion Criteria:

  • Inserts that were sterilized by gamma radiation and exposed to oxygen in packaging.

Study Plan

This section provides details of the study plan, including how the study is designed and what the study is measuring.

How is the study designed?

Design Details

Cohorts and Interventions

Group / Cohort
Mobile bearings
Tibial polyethylene inserts retrieved from total knee replacements where the insert is designed to slide or rotate on the metal baseplate.
Fixed bearings
Tibial polyethylene inserts retrieved from total knee replacements where the insert is locked to the metal baseplate.

What is the study measuring?

Primary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Total Volumetric Wear
Time Frame: At time of revision (average 46 months)
Total volumetric polyethylene wear will be measured among mobile and fixed bearing tibial inserts retrieved during a revision surgery.
At time of revision (average 46 months)

Secondary Outcome Measures

Outcome Measure
Measure Description
Time Frame
Local Volumetric Wear
Time Frame: At time of revision (average 46 months)
Wear from different regions, including the medial articular, lateral articular and backside surfaces, will be evaluated. Maximum linear penetration will also be determined for the medial and lateral compartments.
At time of revision (average 46 months)

Collaborators and Investigators

This is where you will find people and organizations involved with this study.

Collaborators

Investigators

  • Study Director: Robert H Hopper, Jr., PhD, Anderson Orthopaedic Research Institute

Publications and helpful links

The person responsible for entering information about the study voluntarily provides these publications. These may be about anything related to the study.

Study record dates

These dates track the progress of study record and summary results submissions to ClinicalTrials.gov. Study records and reported results are reviewed by the National Library of Medicine (NLM) to make sure they meet specific quality control standards before being posted on the public website.

Study Major Dates

Study Start

June 1, 2010

Primary Completion (Actual)

May 1, 2012

Study Completion (Actual)

May 1, 2012

Study Registration Dates

First Submitted

July 13, 2010

First Submitted That Met QC Criteria

July 19, 2010

First Posted (Estimate)

July 20, 2010

Study Record Updates

Last Update Posted (Estimate)

August 1, 2012

Last Update Submitted That Met QC Criteria

July 30, 2012

Last Verified

July 1, 2012

More Information

Terms related to this study

Other Study ID Numbers

  • AORI2010-0102
  • Study #09010 (Other Grant/Funding Number: DePuy Orthopaedics, Inc.)

This information was retrieved directly from the website clinicaltrials.gov without any changes. If you have any requests to change, remove or update your study details, please contact register@clinicaltrials.gov. As soon as a change is implemented on clinicaltrials.gov, this will be updated automatically on our website as well.

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