Measurement of disc height from lateral radiographic views of the lumbar spine

Objective: Published methods to quantify height of lumbar discs from lateral radiographic views of the lumbar spine yield inaccurate results due to distortion in central projection. Normal values of disc height have not been compiled. Methods: Starting from an analysis of the imaging properties of vertebral bodies in a lateral view and following a logical evolution of Farfan's proposal, a new protocol for the measurement of disc height is given which is independent of distortion. A database of normal values of the height of lumbar discs from T12/L1 to L5/S1 was compiled from 892 lateral views of healthy male and female subjects in the age range between 16 and 57 years. Results: Employing the new protocol, height of all discs on a lateral view can be measured. Variations in position (standing, side-lying) do not influence the result. Retrospective investigations are feasible. The precision of the disc height measurement amounts to 4.15%. Normal, age-appropriate values for the height of lumbar discs are given for the first time. In the individual case, disc height can be quantitatively evaluated by comparison with the normative database. Clinical relevance: The new protocol can be employed to quantitatively identify processes which effect a decrease of disc height. In the individual case, the new protocol and the comparison with the normal database can be employed to quantitatively assess overload injury to lumbar discs in compensation cases.