MRI Study of the Psoas Major Muscle and its Attachments to the Lumbar Intervertebral Discs: Can a Partial or Absent Attachment of the Psoas to the Disc Trigger Herniation of the Disc?

Abstract

Background: The Psoas Major muscle attaches to the discs from its origin until the level of L4-L5 disc. It rarely attaches to the L5-S1 disc, and the absence of attachment of the psoas to the L4-L5 disc is frequently seen. Likewise, disc herniation occurs more often at these two lower lumbar discs L4-L5 and L5-S1. Hypothetically, by attaching the disc, the psoas may provide support to the fibrous annulus and prevent herniation of the nucleus pulposus. That may explain the higher incidence of herniation of the lower lumbar discs where the psoas attachment is frequently absent. Purpose: 1) To search for the location of disc herniation in the lumbar spine, 2) To determine whether the site of the disc herniation coincides with a partial or a total absence of psoas major (PM) attachment to the disc. Materials and Methods: One hundred and seventy-five magnetic resonance imaging (MRI) lumbar spine examinations from Rashid Hospital, Dubai, UAE were reviewed. There were 89 females, and 86 males, twenty-four East Asians and 151 Arabs, mean age 53.2 (range 21-75) years. The participants were selected by one physician. The inclusion criteria were presence of low back pain, paresthesia, radiculopathy. All selected participants underwent MRI spine examinations. All MRI examinations were performed with the same sequences. The MRI images were read by three Radiologists who were blinded to the clinical examination results such as level of dermatomes and side of symptoms. The location and prevalence of nonattachment of the psoas to the three lower discs were assessed. The association of psoas nonattachment to the disc and disc herniation was calculated using the Pearson Chi Square test with 95% confidence interval (CI), and two-sided p value lt;0.05 for statistical significance. Results: At the L5-S1 disc, 16 (9.1%) patients presented with partial attachment of the PM; and 75% of them had disc herniation. One hundred and fifty-nine (90.8%) patients had nonattachment of the PM to the L5