Background: Modular polyethylene inserts
have enabled surgeons to perform an isolated tibial insert exchange while
retaining well fixed components. The purpose of this study was to
review the results of insert revision and to clarify the role of
this option compared with that of revision total knee arthroplasty.
Methods: Fifty-six patients (sixty-three knees)
were managed with revision of a tibial polyethylene insert and retention
of well aligned and stable femoral and tibial components. The implants
had been in situ for an average of fifty-nine months
(range, two to 108 months) at the time of the insert exchange. The
inserts that were removed at the time of exchange were evaluated
with regard to wear of the articular surface according to the classification system
of Hood et al. and with regard to undersurface wear according to
the method described by Wasielewski et al. Forty-eight knees were
followed for an average of 7.4 years (range, 3.0 to 12.2 years)
after the insert exchange. Knees that did not require an additional
operation were considered to have had a successful exchange.
Results: Seven of the forty-eight exchanges
failed, at an average of fifty-four months, because of accelerated
wear of the new insert. All seven knees required complete revision
of all components. Of the twenty-two exchanges that were performed
because of severe wear of the primary insert, six (27 percent) failed
at an average of less than five years; thus, knees in which the
exchange was performed because of advanced wear were more likely
to fail again (p < 0.05). In addition, primary inserts that were
removed from knees in which the exchange procedure subsequently
failed had higher delamination scores than those that were removed
from knees in which the exchange was successful (p < 0.05).
Most of the primary inserts had substantial undersurface wear at
the time of the exchange procedure. Metallosis (thirty knees) and
osteolysis (nineteen knees) were unrelated to failure of the exchange.
Conclusions: An isolated revision of the tibial
polyethylene insert should not be performed when there is accelerated
wear of the insert with severe delamination and grade-3 or 4 undersurface
wear within ten years after the primary procedure. Because a variety
of patient-related, implant-related, and technical factors influence
polyethylene wear, the orthopaedist must consider multiple variables whenever
contemplating a limited revision.