Configuration of the Posterior Lumbar Muscles: Study of Lumbosacral Malformations and the Extraforaminal Approach (ELIF)

Abstract

Purpose: A correlation between the shape of the three posterior lumbar muscles (Multifidus, Longissimus pars lomborum and iliocostalis pars lomborum) and the vertebrae levels has been studied with application to lumbosacral malformations and the extraforaminal approach (ELIF);

Backgrounds: The extraforaminal approach to the lumbar spine makes it possible to treat a very lateral herniation or to perform an interbody fusion with cages (ELIF).The approach is made through a natural cleavage plan between the three posterior lumbar muscles. The shape of these muscles varies with the level of the lumbar spine. To help the surgeon in this intermuscular approach, we have made, at every level, a correlation between the shape of these muscles and the level of the vertebral discs. A pattern has been found, at first, in normal lumbar spines and, in a second time, in spines with lumbosacral malformations.

With lumbosacral malformations, the bony frame is somewhat ambiguous and not always easily described despite a lot of classic markers. The vertebral segmentation, from genetic origin, includes both muscular and bony structures. The global study can help the understanding of the malformations.

Material and Method: During a spine unit consultation, a series of 90 lumbar spines have been studied with X-ray and CT axial horizontal cross-sections, thanks to a special software. At every level, the ratio between the surface of the Multifidus and the global surface of the three posterior lumbar muscles has been calculated.

Among the 90 studied lumbar spines, 59 presented a normal bony frame, and 31 were supposed to have a lumbosacral malformation.

Results: For L5S1, L4L5, L3L4 and L2L3, the normal ratio are, respectively 95%, 51%, 34% and 18%; Any change in these patterns may call for a sacralization with two different forms depending on the number (4 or 5) of the so-called lumbar vertebrae.

Among the 90 studied lumbar spines, 59 presented a normal bony frame, and 31 were supposed to have a lumbosacral malformation.