title: Restoration of the centre of rotation in primary total hip arthroplasty: the influence of acetabular floor depth and reaming technique.
abstract: OBJECTIVE
  One goal of total hip arthroplasty is to restore normal hip anatomy. The aim of this study was to compare displacement of the centre of rotation (COR) using a standard reaming technique with a technique in which the acetabulum was reamed immediately peripherally and referenced off the rim.
  
  
  METHODS
  In the first cohort the acetabulum was reamed to the floor followed by sequentially larger reamers. In the second cohort the acetabulum was only reamed peripherally, starting with a reamer the same size as the native femoral head. Anteroposterior pelvic radiographs were analysed for acetabular floor depth and vertical and horizontal position of the COR.
  
  
  RESULTS
  Horizontally, the mean medial displacement of the COR was 0.8 mm (standard deviation (sd) 1.4) in the peripheral remaing group and 5.0 mm (sd 3.30) in the standard reaming group (p < 0.001). Vertically, the mean superior displacement of the COR was 0.7 mm (sd 1.3) in the peripheral reaming group and 3.7 mm (sd 2.6) in the standard reaming group (p < 0.001). In the standard reaming group, there was a strong correlation between the pre-operative acetabular floor depth and displacement of the COR (p < 0.001).
  
  
  CONCLUSIONS
  Reaming the acetabulum to the floor can lead to significant displacement of the COR medially and superiorly. This displacement is related to the pre-operative acetabular floor depth and cannot always be compensated by using a high offset stem. Cite this article: Bone Joint J 2016;98-B:1597-603.
authors.affiliation: Bravis Hospital, Boerhaaveplein 1, 4624VT Bergen op Zoom, The Netherlands.
authors.forename: G
authors.initials: G
authors.lastname: Meermans
authors.affiliation: Bravis Hospital, Boerhaaveplein 1, 4624VT Bergen op Zoom, The Netherlands.
authors.forename: J Van
authors.initials: JV
authors.lastname: Doorn
authors.affiliation: Bravis Hospital, Boerhaaveplein 1, 4624VT Bergen op Zoom, The Netherlands.
authors.forename: J-J
authors.initials: JJ
authors.lastname: Kats
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000473:pathology / Q000601:surgery*; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000379:methods*; D017760:Bone Malalignment / Q000209:etiology / Q000517:prevention & control; D005260:Female; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000503:physiopathology; D006801:Humans; D008297:Male; D008875:Middle Aged; D015588:Observer Variation; D010384:Pelvic Bones / Q000000981:diagnostic imaging; D011446:Prospective Studies; D011859:Radiography; D016059:Range of Motion, Articular; D015203:Reproducibility of Results; D012399:Rotation; D016896:Treatment Outcome
keywords: Acetabular offset; Centre of rotation; Component position; Reaming; Total hip arthroplasty