Psoas Morphology Differs between Supine and Sitting Magnetic Resonance Imaging Lumbar Spine: Implications for Lateral Lumbar Interbody Fusion

Abstract

Study DesignRetrospective radiological review.PurposeTo quantify the effect of sitting vs supine lumbar spine magnetic resonance imaging (MRI) and change in anterior displacement of the psoas muscle from L1–L2 to L4–L5 discs.Overview of LiteratureControversy exists in determining patient suitability for lateral lumbar interbody fusion (LLIF) based on psoas morphology. The effect of posture on psoas morphology has not previously been studied; however, lumbar MRI may be performed in sitting or supine positions.MethodsA retrospective review of a single-spine practice over 6 months was performed, identifying patients aged between 18–90 years with degenerative spinal pathologies and lumbar MRIs were evaluated. Previous lumbar fusion, scoliosis, neuromuscular disease, skeletal immaturity, or intrinsic abnormalities of the psoas muscle were excluded. The anteroposterior (AP) dimension of the psoas muscle and intervertebral disc were measured at each intervertebral disc from L1–L2 to L4–L5, and the AP psoas:disc ratio calculated. The morphology was compared between patients undergoing sitting and/or supine MRI.ResultsTwo hundred and nine patients were identified with supine-, and 60 patients with sitting-MRIs, of which 13 patients had undergone both sitting and supine MRIs (BOTH group). A propensity score match (PSM) was performed for patients undergoing either supine or sitting MRI to match for age, BMI, and gender to produce two groups of 43 patients. In the BOTH and PSM group, sitting MRI displayed significantly higher AP psoas:disc ratio compared with supine MRI at all intervertebral levels except L1–L2. The largest difference observed was a mean 32%–37% increase in sitting AP psoas:disc ratio at the L4–L5 disc in sitting compared to supine in the BOTH group (range, 0%–137%).ConclusionsThe psoas muscle and the lumbar plexus become anteriorly displaced in sitting MRIs, with a greater effect noted at caudal intervertebral discs. This may have implications in selecting suitability for LLIF, and intra-operative patient positioning.

Initial multi-centre clinical experience with prone transpsoas lateral interbody fusion: Feasibility, perioperative outcomes, and lessons learned

“…Lumbar plexus safety remained a concern. However, prone positioning with the hips neutral to extended seems to lengthen the psoas muscle and draw it and the plexus with it more posteriorly [ 13 , 14 ]. This, combined with a mid-disc initial docking and customized A-P exposure from there, have increased the authors’ comfort with access at L4–5.…”

Prone transpsoas lumbar corpectomy: simultaneous posterior and lateral lumbar access for difficult clinical scenarios

“…25 Additionally, in the traditional lateral decubitus position, knee and hip flexion are typically used to counteract plexus strain but are also known to move the plexus to a more anterior position. 26 So, without the need to de-tension the plexus, the prone position may allow extension of the hips and result in a relatively posterior position of the plexus. 16 This interesting topic certainly requires further study and is currently theoretical.…”

Pneumomediastinum and pneumopericardium as rare complications after retroperitoneal transpsoas lateral lumbar interbody fusion surgery

“…Common complications of LLIF were weakness of hip flexor muscle and pain on anterior thigh caused by psoas muscle injury, or retroperitoneal vascular and ureteral injury. [3–5] However, postoperative pneumomediastinum and pneumopericardium have never been documented. In this case, we observed these complications as a result of the migration of air from the retroperitoneum to the mediastinum and pericardium through the narrow connective pathway of a physiological defect in the diaphragm.…”

“…[1,2] Nevertheless, it has been associated with a few complications, the most typical of which is weakness of hip flexor muscle and pain on anterior thigh caused by psoas muscle injury, or retroperitoneal vascular and ureteral injury. [3–5] However, postoperative pneumomediastinum and pneumopericardium as a result of the migration of air have never been documented. Therefore, the authors report a case of pneumomediastinum and pneumopericardium that occurred after LLIF.…”