title: Radiographic evaluation of factors affecting bearing dislocation in the domed lateral Oxford unicompartmental knee replacement.
abstract: BACKGROUND
  The rate of bearing dislocation with the domed lateral Oxford Unicompartmental Knee Replacement (OUKR) in different series varies from 1% to 6% suggesting that dislocation is influenced by surgical technique. The aim of this study was to identify surgical factors associated with dislocation.
  
  
  METHODS
  Aligned post-operative antero-posterior knee radiographs of seven knees that had dislocated and 87 control knees were compared. Component alignment and position and the alignment of the knee were assessed. All bearing dislocations occurred medially over the tibial wall.
  
  
  RESULTS
  Knees that dislocated tended to be overcorrected: Compared with those that did not dislocate, they were in 2° less valgus (p=0.019) and the tibial components were positioned 2 mm more proximal (p<0.01). Although the relative position of the centre of the femoral component and the tibial component was the same (p=0.8), in the dislocating group the gap between the edge of the femoral component and the top of the wall in flexion was 3mm greater (p=0.019) suggesting that the components were internally rotated.
  
  
  CONCLUSIONS
  To minimise the risk of dislocation it is recommended that the knee should not be overstuffed. This is best achieved by selecting the bearing thickness that just tightens the ligaments in full extension, and re-cutting the tibia if necessary. In addition to minimise the gap between the femoral and tibial components through which the bearing dislocates, the femoral component should be implanted in neutral rotation and should not be internally rotated.
  
  
  METHODS
  Level IV.
authors.affiliation: The Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, UK.
authors.forename: A
authors.initials: A
authors.lastname: Gulati
authors.affiliation: The Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, UK.
authors.forename: S
authors.initials: S
authors.lastname: Weston-Simons
authors.affiliation: The Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, UK.
authors.forename: D
authors.initials: D
authors.lastname: Evans
authors.affiliation: The Nuffield Orthopaedic Centre, Headington, Oxford, UK.
authors.forename: C
authors.initials: C
authors.lastname: Jenkins
authors.affiliation: The Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, UK.
authors.forename: H
authors.initials: H
authors.lastname: Gray
authors.affiliation: The Nuffield Orthopaedic Centre, Headington, Oxford, UK.
authors.forename: C A F
authors.initials: CA
authors.lastname: Dodd
authors.affiliation: The Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, UK; The Nuffield Orthopaedic Centre, Headington, Oxford, UK.
authors.forename: H
authors.initials: H
authors.lastname: Pandit
authors.affiliation: The Nuffield Department of Orthopaedics, Rheumatology and Musculoskeletal Sciences, University of Oxford, Windmill Road, Headington, Oxford OX3 7LD, UK; The Nuffield Orthopaedic Centre, Headington, Oxford, UK. Electronic address: david.murray@ndorms.ox.ac.uk.
authors.forename: D W
authors.initials: DW
authors.lastname: Murray
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019645:Arthroplasty, Replacement, Knee; D006801:Humans; D031221:Knee Dislocation / Q000000981:diagnostic imaging* / Q000209:etiology; D007719:Knee Joint / Q000601:surgery*; D007720:Knee Prosthesis / Q000009:adverse effects*; D008875:Middle Aged; D020370:Osteoarthritis, Knee / Q000601:surgery; D011859:Radiography
keywords: Component positioning; Dislocation; Domed bearing; Unicompartmental knee arthroplasty