title: Progression of an arthrogenic motion restriction after immobilization in a rat experimental knee model.
abstract: BACKGROUND
  Contracture is defined as a decrease in both active and passive ranges of motion after immobilization. A fibrotic change of a capsule is suggested to be one of the main causes of the joint contracture. The goal of this study is to determine the effect of capsule on limiting the range of motion after immobilization.
  
  
  METHODS
  We immobilized the knee joint of 35 rats with an internal fixator with the knee joint flexed at 150 degrees. The rats were sacrificed at 1, 2, 4, 6, 8, 12, and 16 weeks after surgery and the lower extremities were disarticulated at the hip joint. After extra-articular myotomies around the tibia and femur, x-rays were taken to measure the angles of extension of the knee joint under 3 different torques. The measurements were repeated after releasing the posterior capsule in order to observe their effects on knee motion.
  
  
  RESULTS
  Joint contracture was rapidly progressed until 8 weeks and advanced slowly after 8 weeks. After releasing the posterior capsule, both the immobilized and the control groups gained the angle of knee extension. The acquired angle in the immobilized group was significantly greater than in the control group after 4 weeks and became plateau after 8 weeks.
  
  
  CONCLUSIONS
  Joint contracture develops at the early stage of immobilization and progresses over time. The posterior capsule significantly contributes to the limitation in extension.
authors.affiliation: Department of Orthopaedic Surgery, Tohoku University Graduate School of Medicine, 1-1 Seiryomachi, Aobaku, Sendai, Japan.
authors.forename: Eiichi
authors.initials: E
authors.lastname: Chimoto
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Hagiwara
authors.forename: Akira
authors.initials: A
authors.lastname: Ando
authors.forename: Eiji
authors.initials: E
authors.lastname: Itoi
mesh_terms: D000818:Animals; D001835:Body Weight; D001846:Bone Development; D007103:Immobilization; D007719:Knee Joint / Q000502:physiology*; D008297:Male; D023421:Models, Animal; D016059:Range of Motion, Articular; D051381:Rats; D017207:Rats, Sprague-Dawley