title: Heterotopic ossification of the knee joint in intensive care unit patients: early diagnosis with magnetic resonance imaging.
abstract: BACKGROUND
  Heterotopic ossification (HO) is the formation of bone in soft tissues. The purpose of the present study was to evaluate the magnetic resonance imaging (MRI) findings on clinical suspicion of HO in the knee joint of patients hospitalised in the intensive care unit (ICU).
  
  
  METHODS
  This was a case series of 11 patients requiring prolonged ventilation in the ICU who had the following diagnoses: head trauma (nine), necrotising pancreatitis (one), and fat embolism (one). On clinical suspicion of HO, x-rays and MRI of the knee joint were performed. Follow-up x-rays and MRI were also performed.
  
  
  RESULTS
  First x-rays were negative, whereas MRI (20.2 +/- 6.6 days after admission) showed joint effusion and in fast spin-echo short time inversion-recovery (STIR) images a 'lacy pattern' of the muscles vastus lateralis and medialis. The innermost part of the vastus medialis exhibited homogeneous high signal. Contrast-enhanced fat-suppressed T1-weighted images also showed a 'lacy pattern.' On follow-up (41.4 +/- 6.6 days after admission), STIR and contrast-enhanced T1-weighted images depicted heterogeneous high signal and heterogeneous enhancement, respectively, at the innermost part of the vastus medialis, whereas x-rays revealed a calcified mass in the same position. Overall, positive MRI findings appeared simultaneously with clinical signs (1.4 +/- 1.2 days following clinical diagnosis) whereas x-ray diagnosis was evident at 23 +/- 4.3 days (p = 0.002).
  
  
  CONCLUSIONS
  MRI of the knee performed on clinical suspicion shows a distinct imaging pattern confirming the diagnosis of HO earlier than other methods. MRI diagnosis may have implications for early intervention in the development of HO.
authors.affiliation: Department of Radiology, Medical School, University of Ioannina, 45110 Ioannina, Greece. margyrop@cc.uoi.gr
authors.forename: Maria I
authors.initials: MI
authors.lastname: Argyropoulou
authors.forename: Eleonora
authors.initials: E
authors.lastname: Kostandi
authors.forename: Paraskevi
authors.initials: P
authors.lastname: Kosta
authors.forename: Anastasia K
authors.initials: AK
authors.lastname: Zikou
authors.forename: Dimitra
authors.initials: D
authors.lastname: Kastani
authors.forename: Efi
authors.initials: E
authors.lastname: Galiatsou
authors.forename: Athanassios
authors.initials: A
authors.lastname: Kitsakos
authors.forename: George
authors.initials: G
authors.lastname: Nakos
mesh_terms: D000328:Adult; D000368:Aged; D042241:Early Diagnosis; D006801:Humans; D007362:Intensive Care Units; D007719:Knee Joint / Q000473:pathology*; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008297:Male; D008875:Middle Aged; D009999:Ossification, Heterotopic / Q000175:diagnosis* / Q000473:pathology; D011446:Prospective Studies; D013997:Time Factors