TUESDAY, Dec. 3, 2019 (HealthDay News) — Total knee arthroplasty (TKA) converted from medial unicompartmental (or “partial”) knee arthroplasty (UKA) has a risk for revision that is threefold higher than that for primary TKA, according to a study published online Nov. 20 in The Journal of Bone & Joint Surgery.

Anders El-Galaly, M.D., from Aalborg University Hospital in Denmark, and colleagues used data from the Danish Knee Arthroplasty Registry (1997 to 2017) to assess survival of 1,012 TKAs converted from UKAs versus 73,819 primary TKAs and 2,572 revision TKAs.

The researchers found that the survival of TKAs converted from UKAs was comparable with that of revision TKAs (P = 0.42) and significantly inferior to the survival of primary TKAs (P < 0.001). Differences between the groups did not alter this relationship compared with revision TKAs (adjusted hazard ratio, 0.94; 95 percent confidence interval, 0.74 to 1.19) and primary TKAs (adjusted hazard ratio, 3.00; 95 percent confidence interval, 2.47 to 3.66). Differences in the conversion implants (all P ≥ 0.47), experience with revision surgery (all P ≥ 0.06), and the indications for the UKA-to-TKA conversion (all P ≥ 0.27) did not affect survival of TKA converted from UKA. Frequent indications for revisions of TKA converted from UKA (P < 0.001) included instability (26 percent) and unexplained pain (13 percent).

“On the basis of this study, we believe that careful consideration is necessary before using medial UKA as treatment for knee osteoarthritis, as a potential conversion to a TKA decreased implant survival when compared with that following primary TKA,” the authors write.

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