Abstract
Introduction:
Unicompartmental knee arthroplasty (UKA) is becoming an increasingly popular option in single compartment osteoarthritis. As a result, diverse second operations including revisions to total knee arthroplasty (TKA) will also increase. The objective of this study is to investigate the distribution of causes of second operations after UKA.
Methods:
We retrospectively reviewed 695 UKAs performed on 597 patients between January 2003 and December 2011. Except in one case, all UKAs were replaced at the medial compartment of the knee. The UKAs were performed on 559 (80.4%) women's knees and 136 (19.6%) men's knees. The mean age at the time of UKA was 61.5 years. The mobile-bearing designs were those that were predominantly implanted (n = 628 mobile, 90.2%; n = 67 fixed). The mean interval between UKA and second operation was 14.1 months.
Results:
In our study, the burden of a second operation after the initial UKA was 7.3%, and the total number of second operations was 51 (n = 45 mobile, n = 6 fixed). The most common cause of a second operation after a mobile-bearing UKA was the dislocation of the meniscal bearing (34.8%), followed by component loosening (21.7%), the formation of a cement loose body (15.2%), unexplained pain (13%), infection (6.5%), periprosthetic fracture (4.3%), and others (4.4%). For the fixed-bearing UKA, the causes of a second operation were loosening (n = 2), unexplained pain (n = 2), and bearing wear (n = 1). The main causes of either a revision UKA or a conversion to TKA were multiform operations that included bricement, internal fixation for a periprosthetic fracture, isolated bearing changes, open debridement with bearing changes, or implant removal due to early infection. Conversions to TKA during the second operation were performed in 17 cases.
Discussion and conclusion:
The most common cause of a second operation after a mobile-bearing UKA was the dislocation of the bearing, followed by component loosening and the formation of a cement loose body. After a fixed-bearing UKA, component loosening and unexplained pain were the most common. A cause-based approach to the primary and failed UKA may be helpful to minimize the possibility of a second operation and to give rise to a successful outcome of a revision TKA.
