Together with other side effects, the clinical use of steroid appears to produce disorders in the spinal column, especially in young patients. However, morphologic details of steroid induced changes in the spinal column are little known. In this study, mice were treated with daily intramuscular injections of hydrocortisone at doses of 1, 5, and 10 mg/kg body weight for 1, 2, or 4 weeks after 2 weeks of age, and the cartilage plates of the lumbar vertebrae were examined, compared with controls, by light and electron microscopy. Cartilage plates consist of an outer zone, abutting the nucleus pulposus and an inner zone oriented toward the vertebral body. The outer zone is divided into a superficial layer and a deep calcified layer. With steroid therapy, chondrocytes in the inner zone and the superficial layer of the outer zone became degenerative or necrotic. In mice treated with 5 and 10 mg hydrocortisone/kg body weight, ossification appeared earlier in the deep calcified layer than in control animals. After 2 weeks of treatment, the cartilage tissue of the inner zone in mice treated with 10 mg hydrocortisone contained ossification gaps, columnar bone tissue, connecting the bony vertebral body, and the deep calcified layer of the outer zone. The thickness of each layer was measured by light microscopy. By hydrocortisone treatment, the whole of the cartilage plate decreased in thickness, the two cartilage layers of the inner zone and the superficial layer of the outer zone became thinner, and the calcified or ossified layer of the outer zone became widened. These changes were more significant in mice treated with larger doses and for longer periods. The results suggest that degenerative changes induced by steriod in the cartilage plate may suppress the growth of the spinal column and make the cartilage plates susceptible to mechanical stress, causing back troubles, which are often seen in children undergoing long-term steroid treatment.
From Hokkaido Orthopedic Memorial Hospital, and Department of Anatomy, Hokkaido University School of Medicine, Sapporo, Japan