Effects of corticosteroids on mechanical strength of intervertebral joints and vertebrae in dogs.

Dogs with hyperadrenocorticism had a higher incidence of intervertebral joint disease, i.e., disc protrusion or spondylosis. In comparing cases of hyperadrenocorticism with age- and breed-matched controls with hypothyroidism, the incidence was significantly greater than expected. This was not seen, however, in beagle dogs in which the incidence was already high and attributed to chondrodystrophoid tendencies in this breed. To investigate the pathogenesis of this association and its possible relationship to steroid-induced osteopenia, adult dogs were given a placebo, prednisone, or prednisone plus calcium for six months. Torque testing of intervertebral joints revealed a consistent trend of lower force to failure in both prednisone-treated groups, but the difference was not statistically significant. In these dogs with mild to moderate hyperadrenocorticism, compression tests of intact vertebral bodies were not significantly different, but blocks of trabecular bone cut from the vertebral bodies failed at significantly lower compressive forces in both prednisone-treated groups compared with controls. Histomorphometric evaluation of lumbar vertebral trabecular bone revealed that the percentage of bone volume was not significantly decreased in the prednisone-treated groups. Nor was there any difference in the thickness or porosity of vertebral end-plates, which might contribute to weakening of intervertebral ligamentous insertions.