title: Contact patch to rim distance predicts metal ion levels in hip resurfacing.
abstract: BACKGROUND
  Component design, size, acetabular orientation, patient gender, and activity level have been suggested as factors leading to elevated metal ion concentrations after-on-metal hip resurfacing arthroplasty (MMHRA). The calculation of the contact patch to rim (CPR) distance integrates component size, design, and acetabular orientation and may be a good predictor of elevated metal ion levels.
  
  
  OBJECTIVE
  We evaluated the effects and the predictive value of the CPR distance on serum cobalt (CoS) and chromium (CrS) ion levels.
  
  
  METHODS
  We retrospectively studied 182 patients with Conserve Plus MMHRAs at a minimum of 12 months after surgery (median, 57 months; range, 12-165 months). CoS and CrS levels were analyzed using inductively-coupled plasma mass spectrometry. Multiple logistic regression was performed to determine which if any of the factors related to serum ion levels.
  
  
  RESULTS
  Patients with CPR distances of 10 mm or less had a 37-fold increased risk of having elevated CoS of 7 μg/L or higher. Similarly, these patients had an 11-fold increased risk of having elevated CrS of 7 μg/L or higher. Sex and University of California Los Angeles activity scores did not influence the postoperative CoS and CrS levels. The negative predictive value for CPR distance less than 10 mm was 99.3% for CoS greater than 7 μg/L and 98.0% for CrS greater than 7 μg/L.
  
  
  CONCLUSIONS
  Our observations suggest the CPR distance would be a useful indicator to determine which patients are at risk for elevated ion levels. Patients with CPR distances greater than 10 mm need not be monitored unless they become symptomatic.
authors.affiliation: Joint Replacement Institute at St. Vincent Medical Center, 2200 West Third Street, Suite 400, Los Angeles, CA 90057, USA.
authors.forename: James P
authors.initials: JP
authors.lastname: Yoon
authors.forename: Michel J
authors.initials: MJ
authors.lastname: Le Duff
authors.forename: Alicia J
authors.initials: AJ
authors.lastname: Johnson
authors.forename: Karren M
authors.initials: KM
authors.lastname: Takamura
authors.forename: Edward
authors.initials: E
authors.lastname: Ebramzadeh
authors.forename: Harlan C
authors.initials: HC
authors.lastname: Amstutz
mesh_terms: D000077:Acetabulum / Q000503:physiopathology / Q000601:surgery*; D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects / Q000295:instrumentation*; D015415:Biomarkers / Q000097:blood; D001696:Biomechanical Phenomena; D002857:Chromium / Q000097:blood*; D003035:Cobalt / Q000097:blood*; D005260:Female; D006621:Hip Joint / Q000503:physiopathology / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D016015:Logistic Models; D008297:Male; D008875:Middle Aged; D016017:Odds Ratio; D011474:Prosthesis Design; D016059:Range of Motion, Articular; D020127:Recovery of Function; D012189:Retrospective Studies; D012307:Risk Factors; D013054:Spectrophotometry, Atomic; D013997:Time Factors; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D015415:Biomarkers; D002857:Chromium; D003035:Cobalt