title: Acute anterior cruciate ligament stump entrapment in anterior cruciate ligament tears: MR imaging appearance.
abstract: OBJECTIVE
  To describe the magnetic resonance (MR) imaging appearance of anterior cruciate ligament (ACL) stump entrapment in patients who presented with decreased knee extension after rupturing the ACL.
  
  
  METHODS
  MR images in 15 patients who had presented with a block to terminal knee extension after sustaining an ACL tear were retrospectively reviewed. The MR imaging appearances of entrapped ACL stumps were defined and correlated with arthroscopic and histologic findings.
  
  
  RESULTS
  The entrapped ACL stumps had two distinct appearances. Type 1 stumps (n = 11) were characterized by a nodular mass located at the anterior aspect of the intercondylar notch, interposed between the lateral femoral condyle and tibia. Type 2 stumps (n = 4) were characterized by a tonguelike free end and angulation of the stump. Histologic evaluation of the resected specimens showed distorted ACL fibers intermixed with variable fibrosis and inflammation.
  
  
  CONCLUSIONS
  Entrapment of an ACL stump can limit knee extension. The two observed appearances of entrapped ACL stumps likely represent two points along a spectrum of appearances, which possibly includes the cyclops lesion.
authors.affiliation: Department of Radiology, Tri-Service General Hospital, National Defense Medical Center, No. 325, Section 2, Cheng-Kung Rd, Neihu, Taipei 114, Taiwan, ROC. gsh5@seed.net.tw
authors.forename: Guo-Shu
authors.initials: GS
authors.lastname: Huang
authors.forename: Chian-Her
authors.initials: CH
authors.lastname: Lee
authors.forename: Wing P
authors.initials: WP
authors.lastname: Chan
authors.forename: Herng-Sheng
authors.initials: HS
authors.lastname: Lee
authors.forename: Cheng-Yu
authors.initials: CY
authors.lastname: Chen
authors.forename: Joseph S
authors.initials: JS
authors.lastname: Yu
mesh_terms: D000293:Adolescent; D000328:Adult; D016118:Anterior Cruciate Ligament / Q000473:pathology / Q000601:surgery; D000070598:Anterior Cruciate Ligament Injuries; D001182:Arthroscopy; D005260:Female; D006801:Humans; D007594:Joint Loose Bodies / Q000175:diagnosis* / Q000473:pathology / Q000601:surgery; D007718:Knee Injuries / Q000175:diagnosis* / Q000473:pathology / Q000601:surgery; D007719:Knee Joint / Q000473:pathology / Q000601:surgery; D008279:Magnetic Resonance Imaging; D008297:Male; D016059:Range of Motion, Articular / Q000502:physiology*; D012189:Retrospective Studies; D012421:Rupture