Date of Award

Fall 1994

Document Type

Thesis

Degree Name

Master of Science in Biomedical Engineering - (M.S.)

Department

Biomedical Engineering Committee

First Advisor

Clarence W. Mayott

Second Advisor

Michael Pappas

Third Advisor

Georghios Makris

Abstract

Two tests were conducted to examine the wear characteristics of tibial bearings used in total knee replacement systems. Each test consisted of six A/P Glide Tibial Bearings each having a conical control arm. The plastic portion of the conical bearings were all made of UHMWPe. Each of these bearing systems was mounted onto a Co-Cr alloy tibial platform and Co-Cr alloy LCS (low contact stress) femoral component . These test samples were mounted onto the New Jersey Mark III Knee Simulator System. The simulator was configured to produce flexion and axial rotation to simulates normal gait. Each test ran at 2 Hz with saline being sprayed between articulating surfaces. Simulation I tested six UHMWPe bearings with an off-center load applied to the bearing by the femoral component 25° from the articulating surface segment tangent. Simulation II tested three Hylamer® and three UHMWPe bearings without an off-center load.

Hylamer®'s volumetric loss and wear rate were found to be higher then UHMWPe. Hylamer® had a maximum volumetric loss of 12.86 mm3 and a maximum wear rate of 6.19 mm3/million cycles while UHMWPe had a maximum volumetric loss of 3.57 mm3 and a maximum wear rate of 1.67 mm3/million cycles. Hylamer increase in crystallinity slightly increases its yield strength and ultimate tensile strength. However, by increasing the crystallinity, stiffness is also increased. This increase in stiffness increases the contact stress which in turn increases the wear. Although a slight increase in strength is gained when using Hylamer®, wear resistance, an important characteristic for total knee replacement systems, is reduced.

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