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Failure Mechanisms After Unicompartmental and Tricompartmental Primary Knee Replacement with Cement

¹ Department of Orthopaedic Surgery, Haukeland University Hospital, N-5021 Bergen, Norway. E-mail address for O. Furnes: ove.furnes{at}haukeland.no
² Department of Surgical Sciences, University of Bergen, N-5021 Bergen, Norway
³ Section for Epidemiology and Medical Statistics, Department of Public Health and Primary Health Care, University of Bergen, P.O. Box 7804, N-5020 Bergen, Norway

Investigation performed at Department of Orthopaedic Surgery, Haukeland University Hospital, Bergen, Norway

Disclosure: In support of their research for or preparation of this work, one or more of the authors received, in any one year, outside funding or grants in excess of $10,000 from the Norwegian Medical Association's fund for Quality Improvement. Neither they nor a member of their immediate families received payments or other benefits or a commitment or agreement to provide such benefits from a commercial entity. No commercial entity paid or directed, or agreed to pay or direct, any benefits to any research fund, foundation, division, center, clinical practice, or other charitable or nonprofit organization with which the authors, or a member of their immediate families, are affiliated or associated.

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Methods: The rates of failure of primary cemented unicompartmental knee replacements (n = 2288) and tricompartmental total knee replacements (n = 3032) as reported to the Norwegian Arthroplasty Register from January 1994 through December 2004 were compared with use of Kaplan-Meier estimated survival rates and Cox multiple regression.

Results: The ten-year survival probability was 80.1% (95% confidence interval, 76.0% to 84.2%) for unicompartmental knee replacements, compared with 92.0% (95% confidence interval, 90.4 to 93.6%) for total knee replacements, with a relative risk of revision of 2.0 (95% confidence interval, 1.6 to 2.5) (p < 0.001). This increased risk of revision following unicompartmental knee replacement was seen in all age-categories. Unicompartmental knee replacement was associated with an increased risk of revision due to pain (relative risk, 11.3 [95% confidence interval, 4.8 to 26.8]; p < 0.001), aseptic loosening of the tibial component (relative risk, 1.9 [95% confidence interval, 1.2 to 3.0]; p = 0.01) and of the femoral component (relative risk, 4.8 [95% confidence interval, 2.3 to 10.3]; p < 0.001), and periprosthetic fracture (relative risk, 3.2 [95% confidence interval, 1.2 to 8.9]; p = 0.02) as compared with total knee replacement. Unicompartmental knee replacement was associated with a lower risk of infection compared with total knee replacement (relative risk, 0.28 [95% confidence interval, 0.10 to 0.74]; p = 0.01).

Conclusions: The survival of cemented unicompartmental knee replacements is inferior to that of cemented tricompartmental total knee replacements in all age-categories.

Level of Evidence: Therapeutic Level II. See Instructions to Authors for a complete description of levels of evidence.

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