Implant selection and causes of aseptic failure in conversion from unicompartmental to total knee arthroplasty: A high-volume centre series.

PURPOSE: This study aimed to describe the causes of aseptic failure leading to conversion from unicompartmental knee arthroplasty (UKA) to total knee arthroplasty (TKA) and to report implant selection and mid-term outcomes in a high-volume orthopaedic centre. METHODS: In this retrospective single-centre case series, 27 patients (13 women, 14 men; mean age 68.9 years, range 55-81) undergoing conversion from UKA to TKA between January 2013 and December 2020 were included. Causes of UKA failure, type of revision implant (posterior-stabilised PS, constrained posterior-stabilised CPS or legacy constrained condylar knee LCCK), and use of tibial stem extensions were recorded. Implant survival after conversion was estimated using Kaplan-Meier analysis, and re-revision rates were documented. Absolute numbers with percentages were reported. RESULTS: The most common causes of UKA failure were periprosthetic tibial fracture (10/27; 37%), tibial component loosening (8/27; 30%) and progression of osteoarthritis (7/27; 26%). PS implants were used in 17 patients (63%; 6 with cemented tibial stem), CPS in 9 (33%; all with stems) and LCCK in 1 (4%; with stem). Overall, tibial stem extensions were used in 16 cases (59%). At a mean follow-up of 23 months (range 0-89), 2 patients (7%) underwent re-revision: one for tibial loosening and one for instability. Kaplan-Meier analysis estimated a median implant survival of 74 months (SD 17.1; 95% CI: 40.6-107.4 months). CONCLUSION: In this specialised high-volume centre, conversion of UKA to TKA was most performed for mechanical failure or disease progression. Most cases could be managed with PS implants, with selective use of stems or higher constraint when indicated. Re-revisions were rare, but findings should be interpreted cautiously given the small sample size, variable follow-up and potential selection bias. LEVEL OF EVIDENCE: Level IV.