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), and 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 the mean age (P = 0.39), mean body mass index (P = 0.82), and sex distribution (P = 0.27) 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 rerevisions and reoperations and compared between groups.

RESULTS

The 2-year survivorship free of any rerevision after conversion TKA was 96% compared to 75% for UKA-to-UKA revision (P < 0.0001). The most common indications for rerevision 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 rerevision 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.