title: Effect of low loading and joint immobilization for spontaneous repair of osteochondral defect in the knees of weightless (tail suspension) rats.
abstract: BACKGROUND
  Mechanical stimulation has a great influence on articular cartilage regeneration. The objective of this study was to clarify the temporal sequences of spontaneous repair of weightless or immobilized joints.
  
  
  METHODS
  An osteochondral defect was created in the femoral patellar groove of F344 rats. A tail-suspension procedure was performed to control the mechanical environment of the hindlimbs. The experimental knee joints were classified into three conditions: CONT, normal gait; LLB, low load-bearing; LLI, low load and immobilized. The repair processes up to 4 weeks were evaluated histologically.
  
  
  RESULTS
  The knee defects in the CONT and LLB conditions were repaired to a smooth surface with fibrous tissue and highly developed subchondral bone. The knees in the LLI condition had the lowest reformation rate of subchondral bone, although partial regeneration of hyaline cartilage-like tissue was seen at 4 weeks after the operation. Bulges of fibrous tissue from the defects were observed in the LLI condition.
  
  
  CONCLUSIONS
  These results, combined with our previous report, suggest that dynamic compressive strain stimulates regeneration of the joint surface structures. They also suggest that the contact condition of the defect with surface cartilage may play a role in the hyaline cartilage repair.
authors.affiliation: International Innovation Center, Kyoto University, Yoshida-honmachi, Sakyo-ku, Kyoto 606-8501, Japan.
authors.forename: Yasuji
authors.initials: Y
authors.lastname: Harada
authors.forename: Naohide
authors.initials: N
authors.lastname: Tomita
authors.forename: Masaaki
authors.initials: M
authors.lastname: Nakajima
authors.forename: Ken
authors.initials: K
authors.lastname: Ikeuchi
authors.forename: Shigeyuki
authors.initials: S
authors.lastname: Wakitani
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000033:anatomy & histology / Q000293:injuries* / Q000502:physiology*; D005260:Female; D019417:Hindlimb Suspension / Q000502:physiology*; D007719:Knee Joint / Q000502:physiology*; D051381:Rats; D011916:Rats, Inbred F344; D012038:Regeneration; D012075:Remission, Spontaneous; D016474:Weight-Bearing / Q000502:physiology*