LUMBOSACRAL SEGMENTAL MOTION IN NORMAL INDIVIDUALS - HAVE WE BEEN MEASURING INSTABILITY PROPERLY

The utility or futility of flexion-extension radiographs in the diagnosis of lumbar spine segmental instability is a controversial issue. Previous investigations have reported a large range of normal motion and a significant overlap of symptomatic and asymptomatic motion patterns. The authors’ goal was to define normal lumbosacral motion in vivo using ordinary weight-bearing lateral flexion-extension radiographs from 40 volunteers without the use of computers or special X-ray equipment. Calculation of dynamic vertebral translation, defined as the change in relative position from flexion to extension, provided a more accurate assessment of vertebral mo­tion than measurement of static displacement on a flexion or extension view alone. Normal lumbar vertebral levels should have less than 3.0 mm of dynamic anteroposterior (AP) translation (< 8% of vertebral body width). Although 42% of the normal subjects had at least one level with a static olisthesis greater than 3.0 mm in either flexion or extension, only 5% had a dynamic AP translation greater than 3.0 mm. These data have suggested that the previously reported large range of motion and frequency of overlap between symptomatic and asympto­matic patients may be significantly decreased (eightfold) by calculating dynamic motion, rather than static vertebral positions. The authors believe these data will provide the basis for reassessment of flexion-extension radiography in the diagnosis of lumbar spine instability. © Lippincott-Raven Publishers.