Anatomy of the psoas muscle and lumbar plexus with respect to the surgical approach for lateral transpsoas interbody fusion

Abstract

Lateral transpsoas interbody fusion (LTIF) is a minimally invasive technique that permits interbody fusion utilizing cages placed via a direct lateral retroperitoneal approach. We sought to describe the locations of relevant neurovascular structures based on MRI with respect to this novel surgical approach. We retrospectively reviewed consecutive lumbosacral spine MRI scans in 43 skeletally mature adults. MRI scans were independently reviewed by two readers to identify the location of the psoas muscle, lumbar plexus, femoral nerve, inferior vena cava and right iliac vein. Structures potentially at risk for injury were identified by: a distance from the anterior aspect of the adjacent vertebral bodies of <20 mm, representing the minimum retraction necessary for cage placement, and extension of vascular structures posterior to the anterior vertebral body, requiring anterior retraction. The percentage of patients with neurovascular structures at risk for left-sided approaches was 2.3% at L1-2, 7.0% at L2-3, 4.7% at L3-4 and 20.9% at L4-5. For right-sided approaches, this rose to 7.0% at L1-2, 7.0% at L2-3, 9.3% at L3-4 and 44.2% at L4-5, largely because of the relatively posterior right-sided vasculature. A relationship between the position of psoas muscle and lumbar plexus is described which allows use of the psoas position as a proxy for lumbar plexus position to identify patients who may be at risk, particularly at the L4-5 level. Further study will establish the clinical relevance of these measurements and the ability of neurovascular structures to be retracted without significant injury.

Fig. 1

Anterior intervertebral plane (red line) for L2–3 drawn on both sagittal (a) and axial (b) plane images

Fig. 2

Intraoperative fluoroscopic image demonstrating retractor system and location of approach in reference to anterior intervertebral plane (red line)

Fig. 3

Axial MRI image at L3–4 demonstrating measurements in relationship to the anterior intervertebral plane: a the anterior edge of the psoas muscle (extending just anterior to the intervertebral plane in this image), b the anterior aspect of the lumbar plexus, c the location of the femoral nerve beginning the L3–4 level, d the position of the posterior edge of either the inferior vena cava or right iliac vein depending on level, e the anteroposterior diameter of the psoas muscle. The diagram also includes measurement (f), the transverse distance between the lateral aspect of the intervertebral disc and the medial aspect of the lumbar plexus

Fig. 4

Relationship between anterior aspect of the psoas muscle and anterior aspect of lumbar plexus in references to anterior intervertebral plane