title: Reversibility of immobilization-induced articular cartilage degeneration after remobilization in rat knee joints.
abstract: Joint immobilization is commonly used for the treatment of joint injuries, but it causes articular cartilage degeneration. The purpose of this study was to clarify the reversibility of immobilization-induced articular cartilage degeneration using rat knee joints. Immobilization of rat knee joints induces atrophic changes in the non-contact area, loss of chondrocytes in the contact area, and hypertrophy of chondrocytes in the transitional area of the articular cartilage. The unilateral knee joints of adult male rats were rigidly immobilized at 150° of flexion with a plate and screws for 1, 2, and 4 weeks. After the experimental periods, the fixation devices were removed and the rats moved freely for 16 weeks. Sham-operated rats were used as a control. Sagittal sections at medial midcondylar regions of the knee were assessed with histological and histomorphometric methods. Mechanical properties were assessed by measuring the sound speed with scanning acoustic microscope. Reduction of cartilage proteoglycan in the non-contact area was almost reversible, but hypertrophy of chondrocytes in the transitional area and loss of chondrocytes in the contact area were irreversible even at 1-week immobilization-remobilization group. Sound speed of the articular cartilage in the contact area was not restored. These results indicate that atrophic changes through decreased mechanical stress in the non-contact area were reversible, but loss of chondrocytes and hypertrophy of chondrocytes in the contact and transitional areas through increased mechanical stress by rigid immobilization were irreversible after remobilization. Clinicians should be aware that even a short-term rigid immobilization could cause irreversible articular cartilage damage.
authors.affiliation: Department of Orthopaedic Surgery, Tohoku University School of Medicine, 1-1 Seiryomachi, Aoba-ku, Sendai, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Ando
authors.forename: Hideaki
authors.initials: H
authors.lastname: Suda
authors.forename: Yoshihiro
authors.initials: Y
authors.lastname: Hagiwara
authors.forename: Yoshito
authors.initials: Y
authors.lastname: Onoda
authors.forename: Eiichi
authors.initials: E
authors.lastname: Chimoto
authors.forename: Yoshifumi
authors.initials: Y
authors.lastname: Saijo
authors.forename: Eiji
authors.initials: E
authors.lastname: Itoi
mesh_terms: D000818:Animals; D002358:Cartilage, Articular / Q000473:pathology* / Q000502:physiology*; D019902:Chondrocytes / Q000473:pathology; D005269:Femur / Q000473:pathology; D007103:Immobilization; D007719:Knee Joint / Q000473:pathology* / Q000502:physiology*; D008297:Male; D033401:Microscopy, Acoustic; D051381:Rats; D017207:Rats, Sprague-Dawley; D013977:Tibia / Q000473:pathology; D013997:Time Factors