Facet Dimensions, Orientation, and Symmetry at L5-S1 Junction in Lumbosacral Transitional States

Study Design. Study analyses dimensions, angular orientations, and symmetry of articular facets at the L5-S1 junction associated with transitional anomalies comprising (1) L5-S1 accessory articulations; (2) complete sacralization of the L5 vertebrae; and (3) completely lumbarized S1 sacral segments. Data were compared with same parameters evaluated in normal sacrum. Objective. Investigating probable morphologic differences in facet joints at the normal and transition affected lumbosacral junctions. Summary of Background Data. Facet joints at the L5-S1 play an important role in load sharing and imparting stability at this area as well as are involved in conditions such as isthmic spondylolysis, degenerative spondylolisthesis, and osteoarthritis, giving rise to low back pain situations. Several morphologic variations at the lumbosacral junction have been studied and inconsistently alluded to be associated with these painful conditions. Lumbosacral transitional anomalies, on the other hand, have also been linked to low back pain situations. L5-S1 transitions have been shown to be associated with altered L5-S1 articular morphology as well as load-sharing pattern at the region. The analysis of L5-S1 zygapophysial anatomy in context of transitional anomalies at this region has rarely been documented. Methods. Both the superior articulating facets in the normal as well as in transition associated sacra were measured for (1) height, (2) width, (3) surface area, and (4) angulation of the articular surfaces with reference to the midsagittal plane. Data were also analyzed to find structural asymmetry between the two sides. Results. Facets demonstrated smallest linear dimensions, surface areas, and maximum coronal orientation in lumbarized specimens. Facets areas associated with accessory articulations were also smaller and coronally oriented. Sacralization induced insignificant alteration in the facet morphology. Asymmetry (tropism) was observed in facets predominantly associated with accessory L5-S1 articulations. Conclusions. L5-S1 transitions possess altered facet morphology. These alterations are possibly related to low back pain situations.