title: Analysis of displacement and deformation of the medial meniscus with a horizontal tear using a three-dimensional computer model.
abstract: OBJECTIVE
  The displacement and deformation of the knee meniscus significantly affect its roles; however, little is known about the displacement and deformation patterns of a torn medial meniscus. The objective of this study was to evaluate quantitatively the patterns of displacement and deformation in horizontally torn medial menisci during knee flexion.
  
  
  METHODS
  Twenty patients with horizontally torn medial menisci underwent three-dimensional (3-D) magnetic resonance imaging at varying degrees of knee flexion, and 3-D computer models of the tibia, tibial articular cartilage, and meniscus were generated. Based on these, the size of the horizontal tear (% tear) was evaluated and defined as the circumferential ratio between the length of the horizontal tear and that of the entire meniscus. The 3-D meniscus models were automatically superimposed over images taken at 0, 20, 40, and 60° of knee flexion by the voxel-based registration method. Meniscal motion and deformation during knee flexion were visualized and quantitatively calculated on the mid-sagittal plane. Correlations between the size of horizontal tear, displacement/deformation of torn menisci, and clinical symptoms were evaluated after conservative treatment for 3 months.
  
  
  RESULTS
  The % tear was 35.7 ± 12.5 % (range 13.7-55.5 %). During knee flexion, all torn menisci moved posteriorly, with gradual widening of horizontal and vertical gaps (p < 0.05). A direct correlation was observed between % tear and change in the vertical tear gap during knee flexion (p < 0.05). There was an inverse correlation between Lysholm score and % tear (p < 0.05).
  
  
  CONCLUSIONS
  Medial meniscal horizontal tears widen and deform during knee flexion, and % tear correlates with the change in the vertical gap. Patients with a lower % tear are more capable of performing activities of daily living after conservative treatment. This method may help clarify the cause of pain in patients with medial meniscus tears as well as facilitate the selection of an appropriate treatment plan.
  
  
  METHODS
  Case series, Level IV.
authors.affiliation: Department of Sports Orthopedics, Osaka Rosai Hospital, 1179-3 Nagasone-cho, Kita-ku, Sakai, Osaka, 591-8025, Japan, h-amano@umin.ac.jp.
authors.forename: Hiroshi
authors.initials: H
authors.lastname: Amano
authors.forename: Takehiko
authors.initials: T
authors.lastname: Iwahashi
authors.forename: Tomoyuki
authors.initials: T
authors.lastname: Suzuki
authors.forename: Tatsuo
authors.initials: T
authors.lastname: Mae
authors.forename: Norimasa
authors.initials: N
authors.lastname: Nakamura
authors.forename: Kazuomi
authors.initials: K
authors.lastname: Sugamoto
authors.forename: Konsei
authors.initials: K
authors.lastname: Shino
authors.forename: Hideki
authors.initials: H
authors.lastname: Yoshikawa
authors.forename: Ken
authors.initials: K
authors.lastname: Nakata
mesh_terms: D000328:Adult; D003198:Computer Simulation; D005260:Female; D006801:Humans; D021621:Imaging, Three-Dimensional / Q000379:methods*; D007593:Joint Instability / Q000175:diagnosis* / Q000209:etiology / Q000503:physiopathology; D007718:Knee Injuries / Q000150:complications / Q000175:diagnosis* / Q000503:physiopathology; D008279:Magnetic Resonance Imaging / Q000379:methods*; D008592:Menisci, Tibial / Q000473:pathology*; D012421:Rupture