Why Do Lateral Unicompartmental Knee Arthroplasties Fail Today?

In large studies, the failure modes of lateral unicompartmental knee arthroplasty (UKA) are usually presented in combination with medial UKA, which is mainly due to low surgical frequency of lateral UKA. Because lateral UKA differs from medial UKA in anatomic and kinematic characteristics, failure modes of lateral UKA should not be presented in combination with medial UKA. Therefore, we performed a systematic review to assess failure modes in lateral UKA and compared failure modes in cohort studies with those found in registry-based studies. A search performed in PubMed, Embase, and Cochrane identified 25 studies (23 cohort studies and 2 registry-based studies) that were eligible in presenting failure modes in lateral UKA. Most common failure modes in lateral UKA were progression of osteoarthritis (OA; 29%), aseptic loosening (23%), and bearing dislocation (10%). In cohort studies, progression of OA was more common (36%) than bearing dislocation (17%) and aseptic loosening (16%), while in the registry-based studies, aseptic loosening (28%) was more common than progression of OA (24%) and bearing dislocation (5%). In conclusion, progression of OA is the most common failure mode in lateral UKA. In the future, both cohort studies and registry-based studies should report the failure modes of medial and lateral UKA separately.