Papain-induced changes in the knee joints of adult rabbits

Rapidly progressing joint disease can be produced in the rabbit by intra-articular injection of concentrated papain. With the use of radioactive thymidine it is possible to demonstrate that the cartilage cells recover their ability to divide by mitosis at the same time as degenerative changes appear in the cartilage. Clusters of chondrocytes arise by mitosis of chondrocytes and not by a floating together of cartilage cells.

Experimentally induced osteoarthrosis in the temporomandibular joint of the mouse

(1) 6-week-old ICR mice were injected daily with pharmacologic doses of triamcinolone diacetate (1.5 mg/kg body weight) for 8 consecutive weeks. (2) The temporomandibular joint served as a model for histological and histochemical examinations concerning the effect of glucocorticoid hormone upon bone and cartilage. (3) Histochemical reactions indicated a large number of lipid droplets within the peripheral vasculature. (4) Histological examinations revealed pathologic features, indicative of primary osteoarthrosis.

Articular cartilage studies and osteoarthrosis

Osteoarthrosis is characterized in the early stages by degradation of articular cartilage matrix. Clinical, radiological, and pathological studies have failed to reveal the factors which initiate the breakdown of cartilage and are not applicable to detailed sequential studies of the affected tissues at all stages in the disease. Therefore animal experiments have been employed to provide more information on degradation and repair process in cartilage. These studies have demonstrated: 1) Matrix protection and induced repair of mature articular cartilage by the use of oral aspirin after lacerative injury. 2) Establishment by the intra-articular injection of the plant enzyme papain of a model of osteoarthrosis in the rabbit hip which mimics human osteoarthrosis and is suitable for further experimental studies. 3) A proliferation of mature articular cartilage chondrocytes in response to loss of matrix, which indicates a latent repair capacity. 4) Repair of extensively damaged hip joints after femoral osteotomy by increased formation of subchondral new bone and formation of fibrocartilage on the articulating surfaces. These tissue repair processes are associated with an increase in vascularity of the femoral head and acetabulum produced by the osteotomy. 5) Succesful transplantation as allografts in both normal and arthrotic rabbit knees of aggregates of epiphysial chondrocytes isolated from their matrix. This method of joint surface replacement may have clinical applications.

Skeletal effects of cholesterol feeding

The effect of a 4% supplement of cholesterol to a standard diet on knee joints and vertebral columns was investigated in male mice of strain C57B1. The experimental diet was fed from the time of weaning through the 18-month period of observation or from the age of 1 year to the end of the experiment at 18 months of age. The incidence of osteoarthrosis was increased in mice fed cholesterol from the age of 12 months on. The incidence of spondylosis was increased after lifelong feeding as well as after feeding of cholesterol during the second year of life. This increase involved both, spondylosis associated with or uncomplicated by prolapse of intervertebral discs. The incidence of simple disc prolapse was not affected by the experimental diet.