title: Why Do Medial Unicompartmental Knee Arthroplasties Fail Today?
abstract: Failure rates are higher in medial unicompartmental knee arthroplasty (UKA) than total knee arthroplasty. To improve these failure rates, it is important to understand why medial UKA fail. Because individual studies lack power to show failure modes, a systematic review was performed to assess medial UKA failure modes. Furthermore, we compared cohort studies with registry-based studies, early with midterm and late failures and fixed-bearing with mobile-bearing implants.
  
  
  
  Databases of PubMed, EMBASE, and Cochrane and annual registries were searched for medial UKA failures. Studies were included when they reported >25 failures or when they reported early (<5 years), midterm (5-10 years), or late failures (>10 years).
  
  
  
  Thirty-seven cohort studies (4 level II studies and 33 level III studies) and 2 registry-based studies were included. A total of 3967 overall failures, 388 time-dependent failures, and 1305 implant design failures were identified. Aseptic loosening (36%) and osteoarthritis (OA) progression (20%) were the most common failure modes. Aseptic loosening (26%) was most common early failure mode, whereas OA progression was more commonly seen in midterm and late failures (38% and 40%, respectively). Polyethylene wear (12%) and instability (12%) were more common in fixed-bearing implants, whereas pain (14%) and bearing dislocation (11%) were more common in mobile-bearing implants.
  
  
  
  This level III systematic review identified aseptic loosening and OA progression as the major failure modes. Aseptic loosening was the main failure mode in early years and mobile-bearing implants, whereas OA progression caused most failures in late years and fixed-bearing implants.
authors.affiliation: Department of Orthopaedic Surgery, Sports Medicine and Shoulder Service, Hospital for Special Surgery, Weill Medical College of Cornell University, New York, New York.
authors.forename: Jelle P
authors.initials: JP
authors.lastname: van der List
authors.affiliation: Department of Orthopaedic Surgery, Sports Medicine and Shoulder Service, Hospital for Special Surgery, Weill Medical College of Cornell University, New York, New York.
authors.forename: Hendrik A
authors.initials: HA
authors.lastname: Zuiderbaan
authors.affiliation: Department of Orthopaedic Surgery, Sports Medicine and Shoulder Service, Hospital for Special Surgery, Weill Medical College of Cornell University, New York, New York.
authors.forename: Andrew D
authors.initials: AD
authors.lastname: Pearle
mesh_terms: D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects*; D018450:Disease Progression; D019544:Equipment Failure Analysis; D006801:Humans; D007719:Knee Joint / Q000601:surgery*; D007720:Knee Prosthesis / Q000009:adverse effects*; D020370:Osteoarthritis, Knee / Q000601:surgery*; D011474:Prosthesis Design; D011475:Prosthesis Failure; D012042:Registries; D012086:Reoperation; D016896:Treatment Outcome
keywords: early failures; failure rate; medial unicompartmental knee arthroplasty; modes of failure; reasons of failure; unicompartmental knee arthroplasty