Using 'subcement' to simulate the long-term fatigue response of cemented femoral stems in a cadaver model: could a novel preclinical screening test have caught the Exeter matt problem?
Previously, cement was formulated with degraded fatigue properties (subcement) to simulate long-term fatigue in short-term cadaver tests. The present study determined the efficacy of subcement in a 'preclinical' test of a design change with known clinical consequences: the 'polished'-to-'matt' transition of the Exeter stem (revision rates for polished stems were twice those for matt stems). Contemporary stems were bead blasted to give Ra = 1 microm (matt finish). Matt and polished stems were compared in cadaver pairs under stair-climbing loads (three pairs of size 1; three pairs of size 3). Stem micromotion was monitored during loading. Post-test transverse sections were examined for cement damage. Cyclic retroversion decreased for polished stems but increased for matt stems (p < 0.0001). The implant size had a substantial effect; retroversion of (larger) size-3 stems was half that of size-1 stems, and polished size-3 stems subsided 2.5 times more than the others. Cement damage measures were similar and open through-cracks occurred around both stems of two pairs. Stem retroversion within the mantle resulted in stem-cement gaps of 50-150 microm. Combining information on cyclic motion, cracks, and gaps, it was concluded that this test 'predicted' higher revision rates for matt stems (it also implied that polished size-3 stems might be superior to size-1 stems).
Race
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Department of Orthopedic Surgery, SUNY Upstate Medical University, Syracuse, New York 13210, USA. racea@upstate.edu
Miller
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MA
Mann
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D000368:Aged; D000369:Aged, 80 and over; D001843:Bone Cements / Q000737:chemistry*; D002102:Cadaver; D019544:Equipment Failure Analysis; D006622:Hip Prosthesis; D006801:Humans; D008422:Materials Testing; D008875:Middle Aged; D011474:Prosthesis Design
D001843:Bone Cements