Analysis of facet inclinaton - With special reference to segmental instability at the level of non-operated intervertebral space

Segmental instability often occurs at the level adjacent to intervertebral fusion after surgery. The cause is mainly due to disc degeneration at the level, however, the facet joint might play a role as one of the main structural components of a segmental motor segment.This report is to elucidate the relation between segmental instability and the facet joint. Angles of inclination of the facet joints are measured as a indicator for this study.The subjects are 26 cases with cervical spondylotic myelopathy who have had anterior interbody fusion in our clinic. There are 15 males and 11 females, and the average age is 50 years old. The average follow-up period after surgery is 6 years.Before surgery various angles of inclination of the facet joint were observed, but at the time of follow-up they tended to be nearly same showing decreased angles at the lower surface of the joint and increased angles at the upper surface, which produces so-called posterior widening of the joint space.This results suggest that facet inclination might be secondary reaction to segmental instability of the level.