Influence of Partial Facet Removal on the Load Distribution in a Lumbar Motion Segment Subjected to Torsional Moments — A Finite Element Study

Surgical procedures of the lumbar spine often requires partial or complete removal of the facet joints. In some cases the removal may be unilateral and in other circumstances the removal may be bi-lateral. The facet joints are known to make the motion segment stable, particularly when the segment is subjected to torsional moment loading. However, partial removal of facet joints makes the motion segment less stable to applied loads and produces high loads in the remaining facet, disc and ligaments. To compensate for this change in load distribution, which in its extreme may present a risk to neurological structures, fusion surgery is sometimes performed. Decisions whether or not to fuse is often controversial. The need for fusion surgery is obvious in some cases. However, many operative procedures affect the stiffness of the motion segment only to a small degree and do not require fusion surgery. The question of whether to fuse is important since fusion increases the morbidity from spinal surgery, and conversely failure to fuse when biomechanically needed may result in a poor end result. Thus, any further understanding of changes in load distribution in the lumbar motion segment due to surgical procedures will help clinicians in their decision process. Experimental studies on the effect of partial removal of facet joints on stability of the motion segments are sparse because of its complexities. In-vitro experiments have been conducted to study the effects of complete removal of one of the facets. Analytical methods, such as finite element modeling, are well suited for such analyses.