When Disaster Strikes: Conversion of Unicompartmental Knee Arthroplasty to Total Knee Arthroplasty.

Objectives: To investigate the causes of failure in unicompartmental knee arthroplasty (UKA), types of implants used in the revision, evaluate the need to use tibial stems, metal block augmentations and bone grafts during conversion to total knee arthroplasty (TKA) METHODS: In a 10-year retrospective analysis, focusing on cases of UKA failure, our study aimed to categorize early and late failures, determine the primary failure modes, and assess the utilization of bone augmentations and grafts during conversion to TKA. We evaluated patient data, diagnoses, procedure intervals, and follow-up periods to provide a comprehensive understanding of the conversion process.

Results: During the past decade, 301 UKA procedures were performed, with 36 knees (11.96%) requiring conversion to TKA. Patient ages averaged 64.3 years, with varied diagnoses, including osteoarthritis and avascular necrosis. The most common failure mode was component loosening or sinking (52.78%), followed by progression of arthritis (25%). Of the 31 cases with mobile-bearing UKA, 9 (29.03%) developed instability and displacement of the polyethylene. Of the 36 cases converted from UKA to TKA, in 31 (86.11%) a revision tibial component with a tibial stem was used. Metal block augmentation was performed in 19 knees (52,78%). All revised UKAs were converted to cemented TKA, with a focus on addressing tibial side issues, which constituted 72.22% of the revisions.

Conclusion: This study highlights the challenges associated with UKA failure, particularly early failures linked to displaced bearings. Converting from UKA to TKA presents technical hurdles, including rod alignment and utilization. Management of proximal tibial defects with metal block augmentation proves to be a viable approach. The use of modular metal augmentation simplifies the reconstruction process. Although the study has limitations, it contributes valuable information about the complexities of knee arthroplasty conversion.

Level of evidence: Therapeutic study, level IV (case series).