cadera / hip - Active Congress.......

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WEAR OF THE ULTRA
HIGH MOLECULAR
WEIGHT POLYETHYLENE
CUP IN CHARNLEY LFA.
WHAT PROGRESS?
B. M. Wroblewski, P. D. Siney, P. A. Fleming
The John Charnley Research Institute,
Wrightington Hospital, Hall Lane,
Appley Bridge Near Wigan, U.K.
Wear of the ultra high molecular weight polyethylene
(UHMWPE) cup and the resulting
loosening has been shown to limit the long-term
results of the Charnley low-frictional torque
arthroplasty (LFA).
Factors affecting wear rates have been studied:
level of patient activity, effective roughness
of the stainless steel head, impingement and
the possible variations in wear characteristics
of UHMWPE. Since patients’ activity level
cannot be predicted or modifi ed, alternative
materials and modifi cations of the design were
examined.
The Charnley 22.225 mm diameter head in
alumina ceramic in combination with chemically
cross-linked polyethylene has now reached 20
years follow-up. The mean penetration rate
is 0.02 mm/year and none have exceeded
0.41 mm total penetration. No cup has been
revised
Zirconia ceramic in combination with UHMWPE
show 68% of cases having no measurable wear
with a follow-up to 13 years. Reducing the diameter
of the neck of the Charnley stem from 12.5
to 10mm has effectively increased the life of the
arthroplasty by the equivalent of 2mm of wear of
10-20 years. Since the problem of cup wear and
loosening is mechanical rather than biological
the long-term solutions are more likely to come
from materials rather than radical changes of
design of methods of component fi xation.