Synostosis of the joint between the body and greater cornu of the human hyoid bone.

The structure of the joint between the body and the greater cornu in the human hyoid bone was examined histologically in 259 cadavers (16-98 years). Joints were classified into three grades based on histological observations. Grade I showed fibrocartilage without degenerative change in the marginal region of the joint. Grade II showed prominent calcification or ossification on the outer margin of the joint without fusion. Grade III showed bony fusion. Histological changes with age were revealed by a comparison of the prevalences of these three grades among individuals of three age groups: young adult (16-39 years), middle aged (40-69 years), and elderly (70+ years). The frequency of hyoid bones with diarthrodial structure of this joint was compared between the age groups. The mean age of subjects with each grade of histological changes was calculated. Results show that, with age, the proportion of Grade I decreased significantly (P < 0.05) and that of Grade III increased significantly. Joints with diarthrodial structure decreased significantly with age relative to all subjects (P < 0.05). Clefts with necrotic tissue were observed in cartilage along with progressive calcification. The mean age of subjects with the histological changes was significantly higher than that of individuals without such changes (P < 0.05). Calcification and ossification of joints were induced with age from fibrous tissue and cartilage on the outer margin of a joint. The authors suggest that the age changes in the joint between the body and greater cornu of the hyoid bone may affect the mobility of this joint and may be related to masticatory and swallowing functions.