Osteochondroma induced by reflection of the perichondrial ring in young rat radii

In order to investigate the effects of reflection of the perichondrial ring in osteochondroma formation, the perichondrial rings of the epiphyseal growth plates in 42 young rat radii were turned to the metaphyseal periosteum by means of blunt dissection. Seven days after surgery a small nest of chondrocytes appeared on the metaphyseal-diaphyseal bone surface at the level of the tip of the reflected perichondrial ring. From the 9th to the 15th days the histological pattern of the osteochondroma was established. The osteochondroma was not connected with the hypertrophic cartilage of the growth plate. During the third and fourth weeks the osteochondroma began to regress with the disappearance of the cartilage nest. During the development of the lesion the bone grew normally and the growth plate migrated distally while the lesion remained at its initial site. The growth plate zone devoid of perichondrial ring was covered by fibrous connective tissue and no removal of the perichondrial ring occurred. These results suggest that the origin of this osteochondroma is the perichondrial ring cells whose polarity has been surgically changed.