Unicompartmental Knee Arthroplasty to UKA Revisions are Six-Times More Likely to Fail than UKA to Total Knee Arthroplasty Conversions.

Background: Previous studies report high failure rates when unicompartmental arthroplasty (UKA) is revised to another UKA (UKA-to-UKA-revision). There are certain indications, such as polyethylene failure or periprosthetic joint infection (PJI), where UKA-to-UKA-revision may be considered. The purpose of this study was to compare survivorship and failure rates in patients undergoing UKA-to-UKA-revision or UKA to total knee arthroplasty (TKA) conversion for various indications.

Methods: We reviewed 230 UKA patients (241 knees), 94% performed in the medial compartment, who were UKA-to-UKA-revision (n = 24) or converted to TKA (n = 217) from 1995 to 2022. There was no difference in mean age (P = 0.385), mean body mass index (BMI) (P = 0.822), and sex distribution (P = 0.271) between groups. Indications for converting to TKA included aseptic loosening (37%), adjacent compartment osteoarthritis progression (34%), and unexplained pain (21%). Indications for UKA-to-UKA-revision included acute PJI (71%), polyethylene dislocations (12%), and aseptic loosening (12%). Kaplan-Meier survivorship analyses were performed for re-revisions and reoperations and compared between groups.

Results: The 2-year survivorship-free of any re-revision after conversion TKA was 96% compared to 75% for UKA-to-UKA-revision (P < 0.0001). The most common indications for re-revision after UKA-to-UKA-revision were PJI (57%) and polyethylene dislocations (28%), and after TKA conversions were aseptic loosening (41%) and PJI (29%). The 2-year survivorship-free of any reoperation after conversion TKA was 92% compared to 69% in the UKA-to-UKA-revision group (P < 0.0001). Of the UKA-to-UKA-revision cases that were performed for PJI (n = 17), the 2-year survivorship-free from all-cause re-revision was 67%. Of the patients who underwent re-revision in the UKA-to-UKA-revision group five of seven were ultimately converted to TKA.

Conclusions: The 2-year failure rate was six-times higher for UKA-to-UKA-revision or than after conversion to TKA. Surgeons should be aware of the high failure rate when counseling patients presenting with complications where UKA-to-UKA-revision may seem to be a potentially less invasive option.