Transitional Patterns of the Zygapophyseal Joints at the Thoracolumbar Region

Abstract

The level and rate of anatomical changes in the orientation of zygapophyseal joints (ZJs) from the thoracic to the lumbar type is a matter of controversy. So, in this study the superior articular facets of ZJs at the thoracolumbar region were investigated for any deviation from the typical thoracic or lumbar criteria. The study included 20 macerated vertebral columns and axial CT sections on 20 healthy adult subjects. Out of the present results three main types of transitional facets could be differentiated: Coronally oriented Divided facets with the medial surface coronally oriented while the lateral surface was facing posterolaterally Lumbar like with less sagittalization and less concavity. Bilateral asymmetry was found to be a common feature. According to the number of ZJs with atypical facets, three main patterns of orientation changes could be elucidated. Gradual pattern (75%) where there was one coronally oriented ZJ, More gradual type with 2 successive atypical ZJs (10%), Sudden pattern (15%) where the transition occurred over one vertebra as its superior facet was thoracic and the inferior facet was lumbar in type. The process of transition of orientation was found to occur between T10-L1 but most commonly between T11,12. Further study is needed to document the assumption that these patterns of normal variations may be related to the predisposition of low back pain or even disc prolapse.