Total hip replacements with metal-on-metal bearings
Introduction: Th e fi rst generation of metalon- metal bearings were introduced in Great Britain in 1960s. Th ese bearings were abandoned already in early 1970s due to some problems and, primarily, due to a great success of Charnley\'s prosthesis. Since it was later realized that some of the me...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Slovenian Medical Association
2009-12-01
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| Series: | Zdravniški Vestnik |
| Online Access: | http://vestnik.szd.si/index.php/ZdravVest/article/view/419 |
| Summary: | Introduction: Th e fi rst generation of metalon-
metal bearings were introduced in Great
Britain in 1960s. Th ese bearings were abandoned
already in early 1970s due to some
problems and, primarily, due to a great success
of Charnley\'s prosthesis. Since it was later
realized that some of the metal-on-metal
prostheses achieved almost 30-year survival,
the interest in these bearings was renewed in
1990s. In this second generation the material
was again Co-28Cr-6Mo; however, the alloy
was wrought and not cast and can contain
high or low carbon content.
Characteristics: In vivo wear of metal-onmetal
bearings is smaller (0.01 mm/year)
compared to metal-on-polyethylene bearings
(0.2 mm/year). Metal wear particles are
usually nanometer-sized, from 25 to 50 nm,
their number is approximately 100 times
larger than the number of metal particles
formed on metal-on-polyethylene bearings.
Th e eff ect of particles is twofold: local and
systemic. Locally, changes in periprosthetic
tissue related to a hypersensitivity-like reaction
were noticed. Systemically, increased
concentrations of metal ions in serum and
urine were observed. Osteolysis was noted also in the second generation of metal-onmetal
bearings.
Clinical results: Some protheses from the
fi rst generation achived an up to 30-year long
survival. Th e results for the second generation
are currently in a mid-term phase. Depending
on the type of material and design,
diff erences in clinical performance are observed. Survivals between 80% at 8 years and
up to 94% at 10 years were reported.
Conclusions: Total hip replacements with
metal-on-metal bearings show smaller wear
and incidence of osteolysis compared to metal-
on-polyethylene bearings. New problems
may appear, however, related to a systemic
increase of cobalt and chromium and a hypersensitivity
to metals. |
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| ISSN: | 1318-0347 1581-0224 |