title: Does femoral neck to cup impingement affect metal ion levels in hip resurfacing?
abstract: BACKGROUND
  Impingement of the femoral neck with the acetabular component after metal-on-metal hip resurfacing arthroplasty (HRA) is a possible cause of edge loading and accelerated bearing wear. No attempt has been made to correlate radiographic impingement signs and blood metal ion levels.
  
  
  OBJECTIVE
  We (1) compared serum cobalt (CoS) and chromium (CrS) concentrations between patients with and without radiographic impingement signs treated with unilateral HRA, (2) determined whether divot depth on the femoral neck correlated with CoS and CrS, and (3) assessed the predictive value of radiographic impingement signs for high levels of CoS and CrS.
  
  
  METHODS
  A retrospective radiographic review of 141 patients with CoS and CrS analyses yielded 21 patients with and 120 without radiographic impingement signs (controls). Radiographic measurements included divot depth and orientation of the acetabular component to compute the contact patch to rim distance, a measure of functional head coverage. We defined a patient as having radiographic impingement signs if a remodeling of the femoral neck cortex showed a depression matching the predicted path of an impinging acetabular component. CoS and CrS were analyzed by inductively coupled plasma mass spectrometry and the radiographs were taken within 12 months of the last blood draw.
  
  
  RESULTS
  Median CoS and CrS were greater in the impingement group than in controls in patients with less than 10-mm contact patch to rim distances. Divot depth did not correlate with CoS or CrS. In predicting elevated ion levels (≥ 7 μg/L), the presence of a radiographic impingement sign showed a sensitivity of 50% for CoS and 33% for CrS and a specificity of 87% for both CoS and CrS.
  
  
  CONCLUSIONS
  Radiographic impingement signs influenced CoS and CrS only when the functional head coverage was insufficient due to poor socket positioning. Radiographic impingement signs alone were not a good predictor of elevated metal ion levels.
authors.affiliation: Joint Replacement Institute, St Vincent Medical Center, 2200 West Third Street, Suite 400, Los Angeles, CA, 90057, USA.
authors.forename: Michel J
authors.initials: MJ
authors.lastname: Le Duff
authors.forename: Alicia J
authors.initials: AJ
authors.lastname: Johnson
authors.forename: Andrew J
authors.initials: AJ
authors.lastname: Wassef
authors.forename: Harlan C
authors.initials: HC
authors.lastname: Amstutz
mesh_terms: D000077:Acetabulum / Q000000981:diagnostic imaging / Q000601:surgery; D000293:Adolescent; D000328:Adult; D000368:Aged; D019644:Arthroplasty, Replacement, Hip / Q000009:adverse effects* / Q000295:instrumentation*; D015415:Biomarkers / Q000097:blood; D002857:Chromium / Q000097:blood*; D003035:Cobalt / Q000097:blood*; D005260:Female; D057925:Femoracetabular Impingement / Q000097:blood* / Q000000981:diagnostic imaging / Q000209:etiology; D005272:Femur Neck / Q000000981:diagnostic imaging / Q000601:surgery*; D006621:Hip Joint / Q000000981:diagnostic imaging / Q000601:surgery*; D006622:Hip Prosthesis; D006801:Humans; D007477:Ions; D016015:Logistic Models; D008297:Male; D013058:Mass Spectrometry; D061825:Metal-on-Metal Joint Prostheses; D008875:Middle Aged; D016017:Odds Ratio; D011237:Predictive Value of Tests; D011474:Prosthesis Design; D011859:Radiography; D012189:Retrospective Studies; D016896:Treatment Outcome; D055815:Young Adult
chemical_list: D015415:Biomarkers; D007477:Ions; D002857:Chromium; D003035:Cobalt