Lightning Podiums: Smorgasboard - Room 802B

Presented by: M. Moawad


A. Buckland(1), B. Beaubrun(1), E. Isaacs(1), J. Moon(1), P. Zhou(1), S. Horn(1), G. Poorman(1), J. Tishelman(1), L. Steinmetz(1), C. Varlotta(1), L. Day(2), T. Errico(1), P. Passias(1), T. Protopsaltis(1)

(1) New York University Langone Orthopedic Hospital, Division of Spinal Surgery, New York, NY, United States
(2) SUNY Downstate Medical Center, Department of Orthopaedic Surgery, Brooklyn, NY, United States


Introduction: Oblique and trans-psoas approaches have become a popular minimally invasive lumbar fusion technique in recent years. Lumbar plexus injury, particularly femoral nerve injury, is a known potential complication of the oblique and trans-psoas approach, and may be minimized by careful pre-operative assessment of psoas anatomy. Controversy 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 prior to presentation by their spinal surgeon. The aim of this study was to quantify the effect of sitting vs standing in lumbar spine MRI and changes in anterior displacement of the psoas muscle from L1-2 to L4-5 discs.

Methods: A retrospective review of a single-spine practice over a 6-month period was performed, identifying patients aged 18-90 years with degenerative spinal pathologies and lumbar MRIs. Exclusion criteria included previous lumbar fusion, scoliosis, neuromuscular disease, skeletal immaturity, or intrinsic psoas muscle abnormalities. The anteriorposterior (AP) dimensions of the psoas muscle and intervertebral disc were measured bilaterally from L1-2 to L4-5, and the AP psoas: disc ratio (PDR) calculated. The PDR was compared between patients with sitting and supine MRI.

Results: 209 patients were identified with supine MRI and 60 patients with sitting MRI, of which 13 patients had undergone both sitting and standing MRIs (BOTH group). For patients who underwent either standing or sitting MRI, a propensity score match (PSM) was performed to match for age, BMI, and gender to produce two groups of 43 patients. In the BOTH and PSM group, sitting MRI resulted in significantly higher PDR compared with supine MRI at all intervertebral levels except L1-2 (figure 1). The largest difference in AP psoas: disc ratio was noted at the L4-5 disc, with a 32-37% increase in sitting compared to standing (range 0-137%). At L2-3 there was a mean increase of 11.4 - 19.0% in PDR, and at L3-4 there was a mean increase of 17.0 - 30.73% in PDR.

Conclusion: Anteroposterior psoas geometry is altered between sitting and supine posture on MRI with a greater effect at more caudal discs. The assumed posture on MRI lumbar spine should be taken into account when planning suitability, approach, and patient positioning in LLIF procedures.