Background: Despite improvements in the design
and manufacturing of the components used in total knee arthroplasty,
wear of the polyethylene bearing remains a potential source of failure.
One theoretical advantage of modular tibial implants is that, when the
components are well fixed, patients with wear or instability of
the tibial insert can be treated with isolated polyethylene exchange.
The aim of this study was to assess the results of isolated tibial
insert exchange during revision surgery in a relatively large, consecutive
group of patients.
Methods: From 1985 through 1997, we performed fifty-six
isolated tibial insert exchanges in fifty-five patients (twenty-nine
men [one man had bilateral revision] and twenty-six
women; mean age, sixty-six years) primarily because of wear or instability. Patients
with loosening of any of the components, a history of infection,
severe stiffness of the knee, recognized malposition of any component,
or problems with the extensor mechanism were excluded. Twelve knees
had had one, two, or three prior revisions. The duration of follow-up
averaged 8.3 years (range, 1.6 to 16.2 years) after the index arthroplasty
and 4.6 years (range, two to fourteen years) after the revision.
Results: The mean Knee Society knee and function
scores improved from 56 and 50.9 points prior to the revision to
76 and 59 points at the time of final follopcow-up. Fourteen (25%)
of the fifty-six knees subsequently required rerevision at a mean of
only three years (range, 0.5 to 6.8 years) after the tibial insert
exchange. The cumulative survival rate at 5.5 years was 63.5% (95% confidence
interval, 14.4%, with nineteen patients remaining at risk).
Of the twenty-seven knees with preoperative instability, eight were
rerevised and another four were considered failures because of severe
pain. Of the twenty-four knees that were treated with the index
revision because of wear of the insert, five were rerevised. In
addition, one extremity in this group was amputated above the knee
as a result of chronic osteomyelitis of the ankle concomitant with chronic
pain at the site of the total knee arthroplasty and another two
inserts were considered failures because of severe pain.
Conclusions: Isolated tibial insert exchange led
to a surprisingly high rate of early failure. Tibial insert exchange
as an isolated method of total knee revision should therefore be
undertaken with caution even in circumstances for which the modular
insert was designed and believed to be of greatest value.