Long bone growth during prolonged intermittent corticosteroid treatment and subsequent rehabilitation.

Immature A/J mice were treated for up to 7 weeks intermittent doses of triamcinolone hexacetonide and were thereafter allowed to recover for 7 weeks. Qualitative and quantitative morphological measurements were performed on the epiphyseal cartilage plate and diaphyseal bone of the humerus. By the third injection significant structural changes were noted in the cartilaginous tissue followed by a complete cessation of bone growth. The hormonal inhibitory effect on long bone growth lasted throughout the experimental period. However, at the end of the recovery period the length of the humerus was 96% of the normal. In contrast, the humeral width at midshaft and the width of its medullary cavity revealed slower recovery, achieving only 80% of the control values. Following rehabilitation, the growth of experimental epiphyseal plates exceeded that of nontreated animals as their width and the number of hypertrophic chondrocytes were 131% and 125% of their controls respectively. Thus, in A/J mice (a highly susceptible inbred strain of mice) intermittent (every four days) administration of a long-acting corticosteroid hormone arrested endochondral and periosteal bone formation; the former, however, underwent full recovery following the termination of the hormonal treatment.