title: Insufficient acetabular version increases blood metal ion levels after metal-on-metal hip resurfacing.
abstract: BACKGROUND
  Many factors affect the blood metal ion levels after metal-on-metal (MOM) hip arthroplasty. The main surgically adjustable variable is the amount of coverage of the head provided by the cup which is a function of the inclination and version angles. However, most studies have used plain radiographs which have questionable precision and accuracy, particularly for version and large diameter metal heads; further, these studies do not simultaneously assess version and inclination. Thus the relationship between version and blood metal ions levels has not been resolved.
  
  
  OBJECTIVE
  We determined whether cup inclination and version influence blood metal ion levels while adjusting for age at assessment, gender, body mass index, horizontal femoral offset, head size, manufacturer hip type, and Oxford hip score.
  
  
  METHODS
  We prospectively followed 100 individuals (51 females, 49 males) with unilateral MOM hip resurfacing who underwent clinical assessment, CT scanning, and blood metal ion measurement. Multiple regression analysis was used to determine which variables were predictors of blood metal ion levels and to model the effect of these variables.
  
  
  RESULTS
  Only cup inclination, version angles, and gender influenced blood cobalt or chromium levels. Cobalt and chromium levels positively correlated with inclination angle and negatively correlated with version angle. The effect of changes in version angle was less than for inclination angle. Based on our observations, we developed a formula to predict the effect of these parameters on metal ion levels.
  
  
  CONCLUSIONS
  Our data suggest insufficient cup version can cause high blood metal ions after MOM hip arthroplasty. We were unable to show that excessive version caused high levels.
  
  
  METHODS
  Level II, prognostic study. See Guidelines for Authors for a complete description of levels of evidence.
authors.affiliation: Department of Orthopaedic Surgery, Imperial College, Charing Cross Hospital Campus, London SW7 2AZ, UK. a.hart@imperial.ac.uk
authors.forename: Alister J
authors.initials: AJ
authors.lastname: Hart
authors.forename: John A
authors.initials: JA
authors.lastname: Skinner
authors.forename: Johann
authors.initials: J
authors.lastname: Henckel
authors.forename: Barry
authors.initials: B
authors.lastname: Sampson
authors.forename: Fabiana
authors.initials: F
authors.lastname: Gordon
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D000328:Adult; D000368:Aged; D000704:Analysis of Variance; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000295:instrumentation*; D002857:Chromium / Q000097:blood; D003035:Cobalt / Q000097:blood*; D005260:Female; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000503:physiopathology / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D016014:Linear Models; D008131:London; D008297:Male; D008875:Middle Aged; D011446:Prospective Studies; D011474:Prosthesis Design; D018570:Risk Assessment; D012307:Risk Factors; D012737:Sex Factors; D013499:Surface Properties; D013997:Time Factors; D014057:Tomography, X-Ray Computed
chemical_list: D002857:Chromium; D003035:Cobalt