title: T2 relaxometry of the infrapatellar fat pad after arthroscopic surgery.
abstract: OBJECTIVE
  To investigate the T2 relaxation values of the infrapatellar fat pad (IFP) after arthroscopic surgery.
  
  
  METHODS
  This study was approved by the institutional review board; all individuals signed informed consent. We performed MRI in 16 knees from 8 subjects. Prior to imaging, each subject had unilateral arthroscopic knee surgery and an asymptomatic non-operated contralateral knee. We used a 10-echo multiple-TE fast-spin echo pulse sequence for creation of T2 relaxation time maps. Two musculoskeletal radiologists independently placed regions of interest in the IFP, suprapatellar subcutaneous and deep intermuscular adipose tissue. Qualitative assessments were performed to assess fibrotic changes affecting patellar retinaculum and IFP. Statistical analyses of T2 values determined differences between groups, correlation with time after surgery, and cut-off values to differentiate groups.
  
  
  RESULTS
  The average time between arthroscopy and imaging was 3.5 ± 0.4 years. IFP of knees with prior surgery had significantly shorter mean T2 values (133 ± 14 ms) compared with control knees (147 ± 8 ms, P = 0.03). There was no significant difference between operated and control knees regarding T2 values of suprapatellar subcutaneous (P = 0.3) or deep intermuscular adipose tissue (P = 0.2). There was no correlation between IFP T2 values and time after surgery (P > 0.2). IFP T2 values ≤ 139 ms had 75 % sensitivity and 88 % specificity in identifying prior arthroscopy.
  
  
  CONCLUSIONS
  Shortening of T2 relaxation values is present in IFP chronically after arthroscopic surgery and may be an indicator of adipose tissue fibrosis.
authors.affiliation: Musculoskeletal Imaging and Intervention, Department of Radiology, Massachusetts General Hospital and Harvard Medical School, 55 Fruit Street YAW 6048, Boston, MA, 02114, USA, mtorriani@mgh.harvard.edu.
authors.forename: Martin
authors.initials: M
authors.lastname: Torriani
authors.forename: Atul K
authors.initials: AK
authors.lastname: Taneja
authors.forename: Ali
authors.initials: A
authors.lastname: Hosseini
authors.forename: Thomas J
authors.initials: TJ
authors.lastname: Gill
authors.forename: Miriam A
authors.initials: MA
authors.lastname: Bredella
authors.forename: Guoan
authors.initials: G
authors.lastname: Li
mesh_terms: D000273:Adipose Tissue / Q000473:pathology* / Q000601:surgery*; D000328:Adult; D001182:Arthroscopy / Q000009:adverse effects*; D005260:Female; D005355:Fibrosis / Q000209:etiology / Q000473:pathology; D006801:Humans; D008279:Magnetic Resonance Imaging / Q000379:methods; D008297:Male; D008875:Middle Aged; D010329:Patella / Q000473:pathology* / Q000601:surgery*; D011184:Postoperative Period; D015203:Reproducibility of Results; D012680:Sensitivity and Specificity; D016896:Treatment Outcome