The relative contribution of disc and vertebral morphometry to the angle of kyphosis in asymptomatic subjects.

In order to investigate the relative contributions of vertebra and inter-vertebral disk to kyphosis, a series of 100 asymptomatic healthy women (age range 39-91 years) were studied to evaluate lateral dorsal appearances and possible related parameters of bone loss. Subjects underwent lateral dorsal spine radiography and single photon absorptiometry of the radius. There was a significant decrease in physical height in relation to age (P < 0.001) and this was directly related to an increasing thoracic kyphosis (P < 0.005). The angle of kyphosis was better related to the average anterior disc height (P < 0.001) than to average anterior vertebral height. The vertebral body ratio, however (anterior/posterior height), was more strongly related to angle of kyphosis than was disk ratio. The results also showed a fall in the proximal and distal radial bone mineral content with age (P < 0.001). These findings suggest that dorsal kyphosis as part of the ageing process may be as closely related to the physical integrity of the disc as to the vertebral body. Hence, therapy for age related bone mineral loss may have limited effect on a kyphotic deformity of the dorsal spine in otherwise asymptomatic patients.