ABSTRACT
Background: The orientation of superior articular processes in the thoracic & lumbar vertebrae differs. These processes play an important role in weight transmission & determining the range & direction of movements between any two vertebrae. Methods: The present study has been conducted on the articular processes of 510 vertebrae (thoracic:360; lumbar: 150) with the aim to investigate the possible mehanism for the change from a posterolaterally facing superior articular surface in the thoracic region to posteromedially facing curved articular surface in the lumbar region. Results: In thoracic region, the angle varied between 112o to 120o but suddenly decreased to 85o (R) and 92.1o (L) at T12. In lumbar region, it showed a marked decrease at L1(R:32o; L:34.2o) which further decreased upto L3 and again increased upto L5. Thus, the above observations indicated that between T1-T11 the facet was directed posterolaterally, at T12 it was almost posterior and at L1 it changed its orientation to posteromedially and remained so in whole of the lumbar region. This change in orientation of superior articular processes at the thoracolumbar junction was abrupt at T12-L1 level or gradual over T11-L1 in almost equal number of columns. Conclusion: Clinical implication: The pattern of orientation not only guides & limits the excursion of motion segments but also is relevant in axial weight bearing.