Background Balancing the relative advantages and disadvantages of unicompartmental knee arthroplasties (UKAs) against those for TKAs can be challenging. Survivorship is one important end point; arthroplasty registers repeatedly report inferior midterm survival rates, but longer-term data are sparse. Comparing survival directly by using arthroplasty register survival reports also may be inadequate because of differences in indications, implant designs, and patient demographics in patients having UKAs and TKAs. Questions/purposes The aims of this study were to assess the survivorship of UKA in the context of one large, northern European registry, and to compare the rates of survivorship with those of cemented TKAs performed for primary knee osteoarthritis during the same 27-year period. Methods From the Finnish Arthroplasty Register, we obtained the data for 4713 patients undergoing UKAs for primary osteoarthritis (mean age, 63.5 years; minimum followup, 0 years; mean, 6.0 years; range, 0-24 years) who had surgical revision between 1985 and 2011. From this cohort, we calculated the Kaplan-Meier survivorship for revision performed for any reason and compared it with the survivorship of 83,511 patients (mean age, 69.5 years; minimum followup 0 years; mean, 6.4 years; range, 0-27 years) with TKAs treated for primary osteoarthritis during the same period. Data were adjusted for age and sex in a comparative analysis.

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The aim and the method of the study were explained to the participants and they were also informed by a standard written information form. Written informed consent was obtained from participants prior to inclusion in the study to ensure that the participation was voluntary (Declaration of Helsinki 2013).Funding: This research has been supported by a grant from Business Finland as part of a project called "Intelligent Customer-driven Solution for Orthopedic and Pediatric Surgery Care". The funder has not influenced the design, conduct, analysis or reporting of the study.

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The purpose of the present study was to evaluate the significance of shortening the antibiotic treatment duration in prosthetic joint infections (PJI) treated with debridement, antibiotics and implant retention (DAIR). In April 2006 we shortened the total antibiotic treatment duration in total knee arthroplasty (TKA) PJIs from 6 months to 3 months and in total hip arthroplasty (THA) PJIs from 3 months to 2 months. All patients with TKA or THA PJI treated with DAIR between February 2001 and August 2009 were reviewed retrospectively. There were 132 patients treated with DAIR, of whom 86 (65%) completed the antibiotic therapy and were therefore eligible for comparison concerning the length of antibiotic treatment. There were 32 (37%) THA and 54 (63%) TKA PJIs in the comparison. The treatment succeeded in 34 (89.5%) patients treated with longer antibiotic treatment and in 42 (87.5%) of those treated with shorter antibiotic treatment (p 0.78). Our conclusion is that if the patient completes the antibiotic therapy, treatment duration of 3 months in TKA PJIs and 2 months in THA PJIs is as good as longer antibiotic treatment of 6 months or 3 months, respectively, in patients treated with DAIR.