Histopathology of growth plate changes in induced abnormal bone growth in lambs.

Unilateral hip excision arthroplasty in lambs resulted in osteochondrosis developing in distal tibiae and metatarsi of the contralateral pelvic limb. The physeal cartilage of distal tibiae and metatarsi developed clefts which probably represent shear failure. The histopathology of the meataphyseal defects differed between the medial and lateral growth plate sectors. Medially, the lesions were typical of physeal osteochondrosis in other mammals, with disorganized chondrocyte columns, cell death and matrix necrosis. Laterally, metaphyseal defects were predominantly fibrous, and islands of bone formed in physeal cartilage from re-established endochondral ossification. Both medial and lateral metaphyseal defects were associated with disturbed primary spongiosa formation. It is suggested that, in some instances at least, traumatic physeal clefts, resulting from shear failure in previously normal growth cartilage, may interfere with endochondral ossification and produce osteochondrosis.