title: Assessment of cup orientation in hip resurfacing: a comparison of TraumaCad and computed tomography.
abstract: OBJECTIVE
  The orientation of the acetabular component in metal-on-metal hip resurfacing arthroplasty affects wear rate and hence failure. This study aimed to establish if interpretation of pelvic radiographs with TraumaCad software can provide a reliable alternative to CT in measuring the acetabular inclination and version.
  
  
  METHODS
  TraumaCad was used to measure the acetabular orientation on AP pelvis radiographs of 14 painful hip resurfacings. Four orthopaedic surgeons performed each measurement twice. These were compared with measurements taken from CT reformats. The correlation between TraumaCad and CT was calculated, as was the intra- and inter-observer reliability of TraumaCad.
  
  
  RESULTS
  There is strong correlation between the two techniques for the measurement of inclination and version (p <0.001). Intra- and inter-observer reliability of TraumaCad measurements are good (p <0.001). Mean absolute error for measurement of inclination was 2.1°. TraumaCad underestimated version compared to CT in 93% of cases, by 12.6 degrees on average.
  
  
  CONCLUSIONS
  When assessing acetabular orientation in hip resurfacing, the orthopaedic surgeon may use TraumaCad in the knowledge that it correlates well with CT and has good intra- and inter-observer reliability but underestimates version by 12° on average.
authors.affiliation: Warwick Orthopaedics, University Hospital of Coventry and Warwickshire, Coventry, UK. dan_westacott@hotmail.com
authors.forename: Daniel J
authors.initials: DJ
authors.lastname: Westacott
authors.forename: John
authors.initials: J
authors.lastname: McArthur
authors.forename: Richard J
authors.initials: RJ
authors.lastname: King
authors.forename: Pedro
authors.initials: P
authors.lastname: Foguet
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging* / Q000473:pathology; D019644:Arthroplasty, Replacement, Hip / Q000379:methods*; D006622:Hip Prosthesis; D006801:Humans; D015588:Observer Variation; D010149:Postoperative Pain / Q000000981:diagnostic imaging; D011857:Radiographic Image Interpretation, Computer-Assisted / Q000379:methods*; D015203:Reproducibility of Results; D012984:Software; D014057:Tomography, X-Ray Computed / Q000379:methods