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EM Santos*, SA Catledge†, M McClenny*, M Cook†,
YK Vohra†, J Lemons*, KD Moore*, *Division of Orthopaedic
Surgery and †Department of Physics, University of Alabama
at Birmingham, Birmingham, AL
Introduction: Tetragonal Zirconia Polycrystal
(TZP) ceramic femoral heads have been implicated in the failure
of total hip arthroplasty (THA) constructs because of increased
wear at the ceramic-polymer interface.1,2 Our study
examines the surface properties of explanted TZP femoral heads
compared to a factory-sealed control in order to document
whether or not there is a change in the material phase and
the surface hardness. TZP can exist in 3 different phases,
but the tetragonal phase (metastable at room temperature)
is the preferred phase with superior mechanical and wear characteristics
to the monoclinic phase.3,4
Materials and Methods: Nine TZP femoral heads
(28 mm diameter) explanted samples obtained after revision
of THA and a factory-sealed control were examined using light
microscopy (LM), glancing angle x-ray diffraction (XRD) and
a nanoindentor (NI) with NI measurements repeated 15 times
on each sample. The XRD beam was aimed toward the weight bearing
(superior) portion of the sample.
Results and Discussion: LM revealed evidence
of metallic transfer and increased surface roughness was noted
in all samples compared to the control. Figure 1 shows good
correlation between increasing surface monoclinic phase and
decreasing surface hardness.
Samples with longer times of implantation had
increasing monoclinic phase conversions. Monoclinic phase
transformation clearly shows a strong trend toward decreased
hardness leading to surface defects that increase roughness.
The results of this study support the contention that TZP
surfaces can be prone to increased wear and consequent osteolysis
that in most cases ends in implant failure.
References
- Haraguchi K, et. al.; J. Bone Joint Surg.
[Br] 2001; 83-B (7): 996-1000.
- Kim YH, Kim JS, Cho SH; J. Bone Joint Surg.
[Br] 2001; 83-B (5): 742-50.
- Piconi C, Maccauro G; Biomaterials 1999;
20:1-25.
- Cales B; Clin. Orth. Rel. Res. 2000; 379:94-112.
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