ISAKOS: 2019 Congress in Cancun, Mexico

2019 ISAKOS Biennial Congress ePoster #936


Inferior Outcome of UKA Converted to TKA in Comparison to Primary TKA

Michael C. Liebensteiner, MD, PhD, Innsbruck, Tyrol AUSTRIA
Alexander Ruzicka, MD, Innsbruck, Tyrol AUSTRIA
Maximilian Hinz, MD, Innsbruck, Tyrol GERMANY
Hermann Leitner, Innsbruck, Tyrol AUSTRIA
Martin Krismer, Prof., Grinzens, Tyrol AUSTRIA

Medical University Innsbruck, Innsbruck, Tyrol, AUSTRIA

FDA Status Cleared


When converting unicondylar knee arthroplasty to total knee arthroplasty the clinical outcome is significantly inferior than that of primary total knee arthroplasty



To investigate the clinical outcome of patients that underwent conversion of a medial unicondylar knee arthroplasty (UKA) to a total knee arthroplasty (TKA). To compare that outcome to patients that underwent primary TKA. It was hypothesized that patients receiving conversion of an UKA to TKA would show significantly worse knee score outcome (H1) and significantly worse implant survival (H2) than patients with primary TKA.


The study design was retrospective-comparative. Data from the federal state's arthroplasty registry was utilized. Included were patients that had conversion of medial UKA to TKA (UKA-to-TKA group) and patients that had primary TKA (pTKA group) since the introduction of the WOMAC score in the registry. As outcome parameters the WOMAC subscales pain, stiffness and function from one year postoperative were analyzed and compared between the groups (worst 100, best 0). In addition, Kaplan-Meier curves and Log-Rank Test were calculated to compare prosthesis survival.


In the UKA-to-TKA group there were 51 cases (age 67 ±9) and in the pTKA group there were 2247 cases (age 69 ±9).
The one-year WOMAC total score was 33 in the UKA-to-TKA group und 21 in the pTKA group (p < 0.001). Similarly, the WOMAC pain, WOMAC stiffness and WOMAC function scores were significantly worse in the UKA-to-TKA group (p values from 0.001 to 0.007, H1).
The 3 year prosthesis survival was 84% and 96% in the UKA-to-TKA and pTKA groups, respectively. After 5 years the survival rates were 82% and 95%. The 10 year prosthesis survival was 74% and 91% in the UKA-to-TKA and pTKA groups, respectively (p < 0.001, H2).


Based on our findings it is concluded that patients that receive a TKA after UKA have inferior results than those that directly receive a TKA. This is true for both patient-reported knee outcome and prosthesis survival.