title: Are the Oxford(®) medial unicompartmental knee arthroplasty new instruments reducing the bearing dislocation risk while improving components relationships? A case control study.
abstract: BACKGROUND
  The recently introduced Microplasty(®) system is an upgrade of conventional phase III instrumentation. However, little is known of its impact on the position of the implant following the Oxford(®) mobile-bearing unicompartmental knee arthroplasty (UKA). This study investigated whether the Microplasty(®) instrumentation system can improve the positioning of the implant and reduce the rate of early failure.
  
  
  OBJECTIVE
  Microplasty(®) provides a better positioning and decreases the rate of dislocation.
  
  
  METHODS
  The medical records and radiographs of 82 consecutive Oxford(®) UKAs were reviewed retrospectively. The radiographic parameters and prevalence of early failure of 41 UKAs performed with the Microplasty(®) system and 41 UKAs using the conventional instrumentation system were compared. Both groups were comparable in terms of demographics and preoperative status.
  
  
  RESULTS
  The femoral components in the Microplasty(®) group were more contiguously placed and more convergent in relation to the tibial components compared to the conventional instrumentation system (P<0.01). The frequency of bearing dislocation was lower in the Microplasty(®) group (P=0.04). A wide gap and the angle between components were associated with an increased risk of bearing dislocation.
  
  
  CONCLUSIONS
  The Microplasty(®) instrumentation system consistently placed the femoral and tibial components in more contiguous and convergent positions. Such changes in position decreased the risk of bearing dislocations by reducing the space available for bearing rotation.
  
  
  METHODS
  Level III, case control study.
authors.affiliation: Department of Orthopaedics, Seoul St. Mary's Hospital, 137-701 Seoul, Korea; Department of Orthopaedics, The Catholic University of Korea College of Medicine, 137-701 Seoul, Korea.
authors.forename: I J
authors.initials: IJ
authors.lastname: Koh
authors.affiliation: Department of Orthopaedics, Gangseo Himchan Hospital, 157-930 Seoul, Korea.
authors.forename: J H
authors.initials: JH
authors.lastname: Kim
authors.affiliation: Department of Orthopaedics, Seoul St. Mary's Hospital, 137-701 Seoul, Korea.
authors.forename: S W
authors.initials: SW
authors.lastname: Jang
authors.affiliation: Department of Orthopaedics, Seoul St. Mary's Hospital, 137-701 Seoul, Korea.
authors.forename: M S
authors.initials: MS
authors.lastname: Kim
authors.affiliation: Department of Orthopaedics, Seoul St. Mary's Hospital, 137-701 Seoul, Korea.
authors.forename: C
authors.initials: C
authors.lastname: Kim
authors.affiliation: Department of Orthopaedics, Seoul St. Mary's Hospital, 137-701 Seoul, Korea; Department of Orthopaedics, The Catholic University of Korea College of Medicine, 137-701 Seoul, Korea. Electronic address: iy1000@catholic.ac.kr.
authors.forename: Y
authors.initials: Y
authors.lastname: In
mesh_terms: D000368:Aged; D019645:Arthroplasty, Replacement, Knee / Q000009:adverse effects / Q000295:instrumentation* / Q000379:methods; D016022:Case-Control Studies; D005260:Female; D006801:Humans; D007720:Knee Prosthesis / Q000009:adverse effects; D008297:Male; D008875:Middle Aged; D011474:Prosthesis Design; D011475:Prosthesis Failure / Q000209:etiology*; D012189:Retrospective Studies; D012307:Risk Factors; D012399:Rotation
keywords: Joint prosthesis instruments; Knee arthroplasty; Unicompartimental arthroplasty