Several studies have described the radiographic, histological, and morphological changes to the paraspinal muscle in patients with chronic low-back pain due to degenerative diseases of the spine. Gross anatomical illustrations have shown that the psoas muscle lies lateral to the L4-5 vertebrae and subsequently thins and dissociates from the vertebral body at L5-S1 in a ventrolateral course. A "rising psoas" may influence the location of the lumbar plexus and result in transient neurological injury on lateral approach to the spine. It is postulated that axial back pain may be exacerbated by anatomical changes of paraspinal musculature as a direct result of degenerative spine conditions. To their knowledge, the authors present the first reported case of a more anteriorly positioned psoas muscle and its resolution following correction of spondylolisthesis in a 62-year-old woman. This case highlights the dynamic nature of degenerative spinal disorders and illustrates that psoas muscle position can be affected by sagittal balance. Normal anatomical positioning can be restored following correction of spinal alignment.
Keywords: CSA = cross-sectional area; EMG = electromyography; L4–5; PLIF = posterior lumbar interbody fusion; lateral interbody fusion; lumbar; psoas; sagittal balance; spondylolisthesis.