title: Muscle atrophy and metal-on-metal hip implants: a serial MRI study of 74 hips.
abstract: OBJECTIVE
  Muscle atrophy is seen in patients with metal-on-metal (MOM) hip implants, probably because of inflammatory destruction of the musculo-tendon junction. However, like pseudotumors, it is unclear when atrophy occurs and whether it progresses with time. Our objective was to determine whether muscle atrophy associated with MOM hip implants progresses with time.
  
  
  METHODS
  We retrospectively reviewed 74 hips in 56 patients (32 of them women) using serial MRI. Median age was 59 (23-83) years. The median time post-implantation was 83 (35-142) months, and the median interval between scans was 11 months. Hip muscles were scored using the Pfirrmann system. The mean scores for muscle atrophy were compared between the first and second MRI scans. Blood cobalt and chromium concentrations were determined.
  
  
  RESULTS
  The median blood cobalt was 6.84 (0.24-90) ppb and median chromium level was 4.42 (0.20-45) ppb. The median Oxford hip score was 34 (5-48). The change in the gluteus minimus mean atrophy score between first and second MRI was 0.12 (p = 0.002). Mean change in the gluteus medius posterior portion (unaffected by surgical approach) was 0.08 (p = 0.01) and mean change in the inferior portion was 0.10 (p = 0.05). Mean pseudotumor grade increased by 0.18 (p = 0.02).
  
  
  CONCLUSIONS
  Worsening muscle atrophy and worsening pseudotumor grade occur over a 1-year period in a substantial proportion of patients with MOM hip implants. Serial MRI helps to identify those patients who are at risk of developing worsening soft-tissue pathology. These patients should be considered for revision surgery before irreversible muscle destruction occurs.
authors.affiliation: Royal National Orthopaedic Hospital, Brockley Hill , Stanmore, Middlesex.
authors.forename: Reshid
authors.initials: R
authors.lastname: Berber
authors.forename: Michael
authors.initials: M
authors.lastname: Khoo
authors.forename: Erica
authors.initials: E
authors.lastname: Cook
authors.forename: Andrew
authors.initials: A
authors.lastname: Guppy
authors.forename: Jia
authors.initials: J
authors.lastname: Hua
authors.forename: Jonathan
authors.initials: J
authors.lastname: Miles
authors.forename: Richard
authors.initials: R
authors.lastname: Carrington
authors.forename: John
authors.initials: J
authors.lastname: Skinner
authors.forename: Alister
authors.initials: A
authors.lastname: Hart
mesh_terms: D000328:Adult; D000368:Aged; D000369:Aged, 80 and over; D019644:Arthroplasty, Replacement, Hip / Q000295:instrumentation*; D002857:Chromium / Q000097:blood; D003035:Cobalt / Q000097:blood; D018450:Disease Progression; D005260:Female; D006621:Hip Joint / Q000601:surgery*; D006622:Hip Prosthesis / Q000009:adverse effects*; D006801:Humans; D015994:Incidence; D008279:Magnetic Resonance Imaging; D008297:Male; D061825:Metal-on-Metal Joint Prostheses / Q000009:adverse effects*; D008875:Middle Aged; D009133:Muscular Atrophy / Q000453:epidemiology* / Q000209:etiology* / Q000473:pathology; D012086:Reoperation; D012189:Retrospective Studies; D013997:Time Factors
chemical_list: D002857:Chromium; D003035:Cobalt