Anatomical study of the paraspinal approach to the lumbar spine

Abstract

The original description of the paraspinal posterior approach to the lumbar spine was for spinal fusion, especially regarding lumbosacral spondylolisthesis treatment. In spite of the technical details described by Wiltse, exact location of the area where the sacrospinalis muscle has to be split remains somewhat unclear. The goal of this study was to provide topographic landmarks to facilitate this surgical approach. Thirty cadavers were dissected in order to precisely describe the anatomy of the trans-muscular paraspinal approach. The level of the natural cleavage plane between the multifidus and the longissimus part of the sacrospinalis muscle was noted and measurements were done between this level and the midline at the level of the spinous process of L4. A natural cleavage plane between the multifidus and the longissimus part of the sacrospinalis muscle was present in all cases. There was a fibrous separation between the two muscular parts in 55 out of 60 cases. The mean distance between the level of the cleavage plane and the midline was 4 cm (2.4-5.5 cm). In all cases, small arteries and veins were present, precisely at the level of the cleavage plane. We found it possible to easily localize the anatomical cleavage plane between the multifidus part and the longissimus part of the sacrospinalis muscle. First the superficial muscular fascia is opened near the midline, exposing the posterior aspect of the sacrospinalis muscle. Then, the location of the muscular cleft can be found by identifying the perforating vessels leaving the anatomical inter-muscular space.

Fig. 1

The initial description by Wiltse of the paraspinal sacrospinalis-splitting approach to the lumbar spine (1968). Note location of bone grafts after closure of the wound ( left)

Fig. 2

The d1 and d2 distance allow locating the limit between the muscular part and the fascial part of the superficial aspect of the sacrospinalis muscle ( SSm) ( SPIS superior and posterior iliac spine)

Fig. 3

The d3 distance is measured between the muscular cleft between the multifidus and the longissimus parts of the sacrospinalis muscle and the midline at the level of the spinous process of L4

Fig. 4

Exposition of the left L4 and L5 transverse processes through the paraspinal sacrospinalis-splitting approach. Note the emergence of the posterior ramus of the L3 nerve at the cranial part of the surgical approach ( arrow)

Fig. 5

A natural cleavage plane between the multifidus and the longissimus part of the sacrospinalis muscle and a fibrous partition between the two muscular parts is well-visualized on this axial spin-echo T1-weighted magnetic resonance image at L4/L5 level ( arrows)

Fig. 6

In all cases, we noted the presence of small arteries and veins, just at the level of the cleavage plane, arising from this anatomical inter-muscular space and remaining on the surface of the sacrospinalis muscle ( arrows)

Fig. 7

The fibrous partition between the two muscular parts is thicker as one approaches down to the sacrum. This can be visualized on this axial spin-echo T1-weighted magnetic resonance image at L5/S1 level ( arrows)

Fig. 8

The initial description by Wiltse of the paraspinal sacrospinalis-splitting approach to the lumbar spine (1968). Note the course of the posterior ramus of the lumbar nerve in the anatomic cleavage plane between the longissimus part and the multifidus part of the sacrospinalis muscle. We found, in all cases, small perforating vessels having the same course