title: Outcomes of Unicompartmental Knee Arthroplasty After Aseptic Revision to Total Knee Arthroplasty: A Comparative Study of 768 TKAs and 578 UKAs Revised to TKAs from the Norwegian Arthroplasty Register (1994 to 2011).
abstract: BACKGROUND
  The general recommendation for a failed primary unicompartmental knee arthroplasty (UKA) is revision to a total knee arthroplasty (TKA). The purpose of the present study was to compare the outcomes, intraoperative data, and mode of failure of primary UKAs and primary TKAs revised to TKAs.
  
  
  METHODS
  The study was based on 768 failed primary TKAs revised to TKAs (TKA→TKA) and 578 failed primary UKAs revised to TKAs (UKA→TKA) reported to the Norwegian Arthroplasty Register between 1994 and 2011. Patient-reported outcome measures (PROMs) including the EuroQol EQ-5D, the Knee Injury and Osteoarthritis Outcome Score (KOOS), and visual analog scales assessing satisfaction and pain were used. We performed Kaplan-Meier and Cox regression analyses adjusting for propensity score to assess the survival rate and the risk of re-revision and multiple linear regression analyses to estimate the differences between the two groups in mean PROM scores.
  
  
  RESULTS
  Overall, 12% in the UKA→TKA group and 13% in the TKA→TKA group underwent re-revision between 1994 and 2011. The ten-year survival percentage of UKA→TKA versus TKA→TKA was 82% versus 81%, respectively (p = 0.63). There was no difference in the overall risk of re-revision for UKA→TKA versus TKA→TKA (relative risk [RR] = 1.2; p = 0.19), or in the PROM scores. However, the risk of re-revision was two times higher for TKA→TKA patients who were greater than seventy years of age at the time of revision (RR = 2.1; p = 0.05). A loose tibial component (28% versus 17%), pain alone (22% versus 12%), instability (19% versus 19%), and deep infection (16% versus 31%) were major causes of re-revision for UKA→TKA versus TKA→TKA, respectively, but the observed differences were not significant, with the exception of deep infection, which was significantly greater in the TKA→TKA group (RR = 2.2; p = 0.03). The surgical procedure of TKA→TKA took a longer time (mean of 150 versus 114 minutes) and more of the procedures required stems (58% versus 19%) and stabilization (27% versus 9%) compared with UKA→TKA.
  
  
  CONCLUSIONS
  Despite TKA→TKA seeming to be a technically more difficult surgical procedure, with a higher percentage of re-revisions due to deep infection compared with UKA→TKA, the overall outcomes of UKA→TKA and TKA→TKA were similar.
authors.affiliation: The Norwegian Arthroplasty Register, Department of Orthopedic Surgery (T.H.L., A.S., G.H., J.-E.G., and O.F.) and the Departments of Occupational Medicine (S.H.L.L.), and Research and Development (B.R.), Haukeland University Hospital, Bergen, Norway Departments of Clinical Medicine (T.H.L., J.-E.G., and O.F.) and Global Public Health and Primary Care (B.R.), Faculty of Medicine and Dentistry, University of Bergen, Bergen, Norway tesfaye.hordofa.leta@helse-bergen.no.
authors.forename: Tesfaye H
authors.initials: TH
authors.lastname: Leta
authors.affiliation: The Norwegian Arthroplasty Register, Department of Orthopedic Surgery (T.H.L., A.S., G.H., J.-E.G., and O.F.) and the Departments of Occupational Medicine (S.H.L.L.), and Research and Development (B.R.), Haukeland University Hospital, Bergen, Norway.
authors.forename: Stein Håkon L
authors.initials: SH
authors.lastname: Lygre
authors.affiliation: The Norwegian Arthroplasty Register, Department of Orthopedic Surgery (T.H.L., A.S., G.H., J.-E.G., and O.F.) and the Departments of Occupational Medicine (S.H.L.L.), and Research and Development (B.R.), Haukeland University Hospital, Bergen, Norway.
authors.forename: Arne
authors.initials: A
authors.lastname: Skredderstuen
authors.affiliation: The Norwegian Arthroplasty Register, Department of Orthopedic Surgery (T.H.L., A.S., G.H., J.-E.G., and O.F.) and the Departments of Occupational Medicine (S.H.L.L.), and Research and Development (B.R.), Haukeland University Hospital, Bergen, Norway.
authors.forename: Geir
authors.initials: G
authors.lastname: Hallan
authors.affiliation: The Norwegian Arthroplasty Register, Department of Orthopedic Surgery (T.H.L., A.S., G.H., J.-E.G., and O.F.) and the Departments of Occupational Medicine (S.H.L.L.), and Research and Development (B.R.), Haukeland University Hospital, Bergen, Norway Departments of Clinical Medicine (T.H.L., J.-E.G., and O.F.) and Global Public Health and Primary Care (B.R.), Faculty of Medicine and Dentistry, University of Bergen, Bergen, Norway.
authors.forename: Jan-Erik
authors.initials: JE
authors.lastname: Gjertsen
authors.affiliation: The Norwegian Arthroplasty Register, Department of Orthopedic Surgery (T.H.L., A.S., G.H., J.-E.G., and O.F.) and the Departments of Occupational Medicine (S.H.L.L.), and Research and Development (B.R.), Haukeland University Hospital, Bergen, Norway Departments of Clinical Medicine (T.H.L., J.-E.G., and O.F.) and Global Public Health and Primary Care (B.R.), Faculty of Medicine and Dentistry, University of Bergen, Bergen, Norway.
authors.forename: Berit
authors.initials: B
authors.lastname: Rokne
authors.affiliation: The Norwegian Arthroplasty Register, Department of Orthopedic Surgery (T.H.L., A.S., G.H., J.-E.G., and O.F.) and the Departments of Occupational Medicine (S.H.L.L.), and Research and Development (B.R.), Haukeland University Hospital, Bergen, Norway Departments of Clinical Medicine (T.H.L., J.-E.G., and O.F.) and Global Public Health and Primary Care (B.R.), Faculty of Medicine and Dentistry, University of Bergen, Bergen, Norway.
authors.forename: Ove
authors.initials: O
authors.lastname: Furnes
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000379:methods*; D005260:Female; D006801:Humans; D053208:Kaplan-Meier Estimate; D008297:Male; D008875:Middle Aged; D009664:Norway; D020370:Osteoarthritis, Knee / Q000601:surgery*; D010147:Pain Measurement; D011474:Prosthesis Design; D011475:Prosthesis Failure; D011788:Quality of Life; D012086:Reoperation; D011795:Surveys and Questionnaires; D016896:Treatment Outcome