title: MRI observations at return to play of clinically recovered hamstring injuries.
abstract: BACKGROUND
  Previous studies have shown that MRI of fresh hamstring injuries have diagnostic and prognostic value. The clinical relevance of MRI at return to play (RTP) has not been clarified yet. The aim of this study is to describe MRI findings of clinically recovered hamstring injuries in amateur, elite and professional athletes that were cleared for RTP.
  
  
  METHODS
  We obtained MRI of 53 consecutive athletes with hamstring injuries within 5 days of injury and within 3 days of RTP. We assessed the following parameters: injured muscle, grading of injury, presence and extent of intramuscular signal abnormality. We recorded reinjuries within 2 months of RTP.
  
  
  RESULTS
  MRIs of the initial injury showed 27 (51%) grade 1 and 26 (49%) grade 2 injuries. Median time to RTP was 28 days (range 12-76). On MRI at RTP 47 athletes (89%) had intramuscular increased signal intensity on fluid-sensitive sequences with a mean longitudinal length of 77 mm (±53) and a median cross-sectional area of 8% (range 0-90%) of the total muscle area. In 22 athletes (42%) there was abnormal intramuscular low-signal intensity. We recorded five reinjuries.
  
  
  CONCLUSIONS
  89% of the clinically recovered hamstring injuries showed intramuscular increased signal intensity on fluid-sensitive sequences on MRI. Normalisation of this increased signal intensity seems not required for a successful RTP. Low-signal intensity suggestive of newly developed fibrous tissues is observed in one-third of the clinically recovered hamstring injuries on MRI at RTP, but its clinical relevance and possible association with increased reinjury risk has to be determined.
authors.affiliation: Department of Orthopaedics, Erasmus Medical Centre, Rotterdam, The Netherlands Department of Sports Medicine, Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.
authors.forename: Gustaaf
authors.initials: G
authors.lastname: Reurink
authors.affiliation: Department of Sports Medicine, Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.
authors.forename: Gert Jan
authors.initials: GJ
authors.lastname: Goudswaard
authors.affiliation: Department of Sports Medicine, Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.
authors.forename: Johannes L
authors.initials: JL
authors.lastname: Tol
authors.affiliation: Department of Radiology, Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.
authors.forename: Emad
authors.initials: E
authors.lastname: Almusa
authors.affiliation: Department of Sports Medicine, Bergman Clinics, Naarden, The Netherlands.
authors.forename: Maarten H
authors.initials: MH
authors.lastname: Moen
authors.affiliation: Department of Sports Medicine, Aspetar Orthopaedic and Sports Medicine Hospital, Doha, Qatar.
authors.forename: Adam
authors.initials: A
authors.lastname: Weir
authors.affiliation: Department of Orthopaedics, Erasmus Medical Centre, Rotterdam, The Netherlands.
authors.forename: Jan A N
authors.initials: JA
authors.lastname: Verhaar
authors.affiliation: Department of Sports Medicine, High Performance Sport New Zealand, Millennium Institute of Sport and Health, Mairangi Bay, Auckland, New Zealand.
authors.forename: Bruce
authors.initials: B
authors.lastname: Hamilton
authors.affiliation: Department of Radiology, Academic Medical Centre University of Amsterdam, Amsterdam, The Netherlands.
authors.forename: Mario
authors.initials: M
authors.lastname: Maas
mesh_terms: D000293:Adolescent; D000328:Adult; D001265:Athletic Injuries / Q000503:physiopathology / Q000534:rehabilitation*; D004311:Double-Blind Method; D006801:Humans; D008279:Magnetic Resonance Imaging; D008297:Male; D008875:Middle Aged; D020127:Recovery of Function; D012008:Recurrence; D013708:Tendon Injuries / Q000534:rehabilitation*; D055815:Young Adult
keywords: Hamstring injuries; MRI; Muscle damage/injuries