Is isolated insert exchange a valuable choice for polyethylene wear in metal-backed unicompartmental knee arthroplasty?

Abstract

Purpose: The aim of this study was to evaluate the clinical outcome and survival rate after isolated liner exchange for polyethylene (PE) wear in well-fixed metal-backed fixed-bearing unicompartmental knee arthroplasty (UKA).

Methods: Twenty medial UKAs in 19 patients [mean age 68.7 years ± 8.7 (range 48.5-81.5 years)] operated on for a direct PE liner exchange after isolated PE wear between 1996 and 2010 in two institutions were retrospectively reviewed. The mean delay between the index operation and revision was 8.2 years ± 2.6 (range 4.8-12.8 years). A four-level satisfaction questionnaire was used, and clinical outcomes were assessed using Knee Society scores (KSS) and range of motion (ROM) evaluation. Radiological evaluation analysed the position of the implants and progression of the disease. Survival rate of the implants was evaluated using Kaplan-Meier analysis with two different end-points.

Results: At the last follow-up [mean 6.8 years ± 5.2 (range 1.1-15.9 years)], 15 patients (79 %) were enthusiastic or satisfied. KSS improved from 73.4 to 86.4 points (p = 0.01) and function from 58.9 to 89.2 points (p < 0.001). ROM at last FU was 126.5° ± 10.3°. The survival rate at 12 years considering "revision for any reason" as the end-point was 71.3 ± 15.3 %, and the survival rate at 12 years considering "revision of UKA to TKA" as the end-point was 93.3 ± 6.4 %.

Conclusion: Isolated liner exchange for PE wear in well-fixed metal-backed fixed-bearing UKA represents a valuable treatment option in selective patients with durable improvement of clinical outcomes without compromising any future revision.

Level of evidence: Retrospective therapeutic study, Level IV.

Keywords: Clinical outcome; Implant survival rate; Isolated replacement of polyethylene; Polyethylene wear; Unicompartmental knee arthroplasty.