Lumbar intervertebral disc heights in normal subjects and patients with disc herniation

A method for the measurement of intervertebral disc heights from lateral radiographs obtained in controlled conditions was examined for intra- and interobserver errors. The use of a strict criterion for the positioning of marks on the images of the vertebrae was shown to enable reproducible measurements to be made with a maximum error of 0.7 mm. Measurements of anterior and posterior disc heights and disc depths were made for 11 normal subjects and ten male patients with prolapsed intervertebral discs, while standing upright. The level of the prolapsed discs were shown to have reduced height compared with normal before surgery, and further narrowing 3 months after surgery. The unaffected discs of the patients were the same height as those of the controls. The technique is proposed as suitable for the investigation of the effect on intervertebral discs of procedures such as the injection of chymopapain.