title: Pseudotumor formation and serum ions after large head metal-on-metal stemmed total hip replacement. Risk factors, time course and revisions in 706 hips.
abstract: BACKGROUND
  The incidence and natural course of pseudotumors in metal-on-metal total hip arthroplasties is largely unknown. The objective of this study was to identify the true incidence and risk factors of pseudotumor formation in large head metal-on-metal total hip arthroplasties.
  
  
  METHODS
  Incidence, time course and risk factors for pseudotumor formation were analysed after large femoral head MoM-THA. We defined a pseudotumor as a (semi-)solid or cystic peri-prosthetic soft-tissue mass with a diameter ≥2 cm that could not be attributed to infection, malignancy, bursa or scar tissue. All patients treated in our clinic with MoM-THA's were contacted. CT scan, metal ions and X-rays were obtained. Symptoms were recorded.
  
  
  RESULTS
  After median follow-up of 3 years, 706 hips were screened in 626 patients. There were 228 pseudotumors (32.3 %) in 219 patients (35.0 %). Pseudotumor formation significantly increased after prolonged follow-up. Seventy-six hips (10.8 %) were revised in 73 patients (11.7 %), independent risk factors were identified. Best cutoff point for cobalt and chromium was 4 μg/l (68 and 77 nmol/l).
  
  
  CONCLUSIONS
  This study confirms a high incidence of pseudotumors, dramatically increasing after prolonged follow-up. Risk factors for pseudotumors are of limited importance. Pain was the strongest predictor for pseudotumor presence; cobalt chromium and swelling were considered poor predictors. Cross-sectional imaging is the main screening tool during follow-up.
authors: , pc Hoofdstraat 13, 8023, AJ, Zwolle, The Netherlands, Bosker.bh@gmail.com.
authors: B H
authors: BH
authors: Bosker
authors: H B
authors: HB
authors: Ettema
authors: M
authors: M
authors: van Rossum
authors: M F
authors: MF
authors: Boomsma
authors: B J
authors: BJ
authors: Kollen
authors: M
authors: M
authors: Maas
authors: C C P M
authors: CC
authors: Verheyen
mesh_terms: D000328:Adult; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation*; D002857:Chromium / Q000097:blood; D003035:Cobalt / Q000097:blood; D005260:Female; D006104:Granuloma, Plasma Cell / Q000097:blood / Q000453:epidemiology* / Q000209:etiology; D006621:Hip Joint / Q000473:pathology / Q000601:surgery; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D015994:Incidence; D007477:Ions / Q000097:blood; D008297:Male; D061825:Metal-on-Metal Joint Prostheses / Q000009:adverse effects*; D008875:Middle Aged; D015207:Osteoarthritis, Hip / Q000097:blood / Q000601:surgery; D011474:Prosthesis Design; D011475:Prosthesis Failure; D012086:Reoperation; D012307:Risk Factors; D013997:Time Factors
chemical_list: D007477:Ions; D002857:Chromium; D003035:Cobalt