The natural history of radiolucencies following cemented unicompartmental knee arthroplasty at 7 years.

INTRODUCTION

Radiolucent lines (RLLs) following unicompartmental knee arthroplasty (UKA) can be concerning as aseptic loosening remains a cause of failure in UKA. The aim of our study was to report on the history of RLLs surrounding the components in a cemented medial compartment fixed-bearing UKA as well as the long-term functional outcomes in this group of patients.

MATERIAL AND METHODS

In this retrospective consecutive case-series, twenty-eight patients (37 knees) were treated with medial, fixed-bearing cemented unicompartmental knee arthroplasty. At average final follow-up of 7.1 years, 36 knees were available for review. Radiographs were taken at six weeks, one year, and final follow up. RLLs were measured using a novel modification to the Knee Society scoring (KSS) system.

RESULTS

At six-weeks, we identified RLLs in 26 tibias and two femurs out of 37 total knees. At one-year, four additional tibias and both femurs showed some progression of their radiolucencies but were < 2 mm total. At final follow-up, 31 of the 36 tibias (86.1%) and five of the 36 femurs (13.9%) had any RLLs. On the tibial side, RLLs were most common in medial/lateral and anterior/posterior aspects of the tibial tray with few found centrally. On the femoral side, the posterior femoral cut accounted for the most RLLs of any zone at all time points. KSS averaged 93.8 at final follow-up and none of the patients required revision surgery.

CONCLUSION

RLLs are common following cemented, fixed-bearing UKA. Many seem to progress slowly up to one year but not thereafter. There does not appear to be any association between the presence of these radiolucencies and long-term follow-up function in this group of patients.