Introduction: Several studies have described the radiographic, histologic, and morphologic changes to the paraspinal muscle in patients with chronic low back pain due to degenerative diseases of the spine. Gross anatomic illustrations have shown that the psoas muscle lies lateral to the L4-5 vertebra and subsequently thins and dissociates from the vertebral body at L5-S1 in a ventral and lateral course. A “rising psoas” may influence the location of the lumbar plexus and result in transient neurologic injury on lateral approach to the spine. It is postulated that axial back pain may be exacerbated by anatomic changes of paraspinal musculature as a direct result of degenerative spine conditions. We present the first reported case of “rising psoas muscle” and its resolution following correction of spondylolisthesis.
Methods: A 62 year-old woman presented with several months of progressively worsening lower back and right leg pain that failed to improve with conservative measures. Neurological exam demonstrated mild right EHL weakness (4+/5). Standing lateral x-ray (Figure 1) and sagittal and axial MRI (Figure 2) imaging showed a grade 2 L4-5 spondylolisthesis and a broad disc protrusion causing foraminal stenosis with moderate central canal compromise. The psoas muscle can be seen rising away from the vertebral body bilaterally.
Results: The patient underwent a L4-5 lateral interbody fusion followed by placement of percutaneous pedicle screws (Figure 3). There were no intraoperative complications. The patient recovered well with complete resolution of her symptoms. A follow-up MRI demonstrated anatomic reduction of the spondylolisthesis and resolution of the foraminal and central stenosis by indirect decompression (Figure 4). Of note, the psoas muscle can now be seen lying lateral to the vertebra at L4-5 in its normally described anatomic position in contrast to the preoperative imaging.
Conclusions: This case highlights the dynamic nature of degenerative spinal disorders and illustrates that psoas muscle position can be affected by sagittal balance. Normal anatomic positioning can be restored following correction of spinal alignment.
Patient Care: This study will improve patient care by highlighting the pathogenesis of chronic back pain and reviewing radiographic characteristics and effects of degenerative spinal diseases on paraspinal and psoas muscle. Patients should be counseled prior to surgery to communicate expectations and obtain informed consent.
Learning Objectives: By the conclusion of this session, participants should be able to: 1) Describe the normal anatomy of paraspinal and psoas muscle, 2) Discuss, in small groups, the clinical and radiographic characteristics of “rising psoas” muscle as it relates to degenerative spinal conditions, and 3) Identify an effective treatment plan that takes into consideration these anatomic variations.