Lateral unicompartmental knee replacement: a systematic review of reasons for failure

PURPOSE: Currently, individual studies lack the power to successively illustrate different failure modes; therefore, we undertook a systematic review to examine lateral unicompartmental knee replacement (lat UKR) failure modes. Furthermore, we compared early with midterm and late failures and fixed-bearing with mobile-bearing implants.  

METHODS: A search using the databases of PubMed, EMBASE, Cochrane, and annual registries was performed to search for failed lat UKRs. Studies were included when they reported more than four failures, described failure modes and were minimum level IV studies. Data was analysed based on overall failure modes, fixed- vs. mobile bearing and early (<5 years) vs. midterm (5-10 years) vs. late failures (>10 years).  

RESULTS: Fourteen cohort studies and two registry-based studies were included. A total of 336 overall failures, 87 time-dependent failures, and 175 implant-specific failures were identified. The main overall causes of failure were osteoarthritis (OA) progression (30%) and aseptic loosening (22%). These were followed by less common causes such as instability (7%), unexplained pain (5%), infection (5%), polyethylene wear (5%), and bearing dislocation (5%). Bearing dislocation was the most common early failure (29%) and also the most common failure among mobile-bearing implants (27%). In midterm and late failures, OA progression had the highest rates (59% and 78% respectively) and was also the most common type of failure in fixed-bearing implants (44%).  

CONCLUSIONS: Progression of OA and aseptic loosening are the major overall failure modes in lat UKR. Bearing dislocation was the main failure mode in early years and in mobile-bearing implants, whereas OA progression caused most failures in late years and in fixed-bearing implants.  

LEVEL OF EVIDENCE: Systematic Review of minimum level IV studies.