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.
George C. Babis, MD; Department of Orthopaedic Surgery, University of Athens, “KAT” Accident Hospital, 2 Nikis Str., GR 145 61 Kifissia, Athens, Greece
Robert T. Trousdale, MD; Bernard F. Morrey, MD; Department of Orthopedics, Mayo Clinic and Mayo Foundation, 200 First Street S.W., Rochester, MN 55905