Background: Concern exists regarding the durability of
unicompartmental knee replacements. The purpose of the present study was to
compare the early failure rates and failure mechanisms of primary cemented
unicompartmental knee replacements with those of primary cemented
tricompartmental total knee replacements.
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.