Anatomic Variation with Supine to Prone Positioning: Implications for Prone Transpsoas Single-Position Lumbar Fusion

Area of Science:

• Spinal surgery
• Anatomy
• Medical imaging

Background:

• The prone transpsoas (PTP) approach allows lateral lumbar interbody fusion (LLIF) in a single prone position.
• This technique offers advantages like circumferential fusion without patient repositioning.
• However, PTP presents challenges including hemodynamic shifts and anatomical navigation difficulties.

Purpose of the Study:

• To describe anatomical shifts in the lumbar spine when patients transition from supine to prone positions.
• To quantify changes in the position of key structures relevant to the PTP approach.

Main Methods:

• Retrospective review of 74 patients undergoing posterior lumbar fusion.
• Comparison of preoperative supine MRI with intraoperative prone CT scans.
• Measurement of anteroposterior (AP) and mediolateral (ML) distances to great vessels and psoas major muscle.

Main Results:

• Significant AP translation of the inferior vena cava, aorta, and iliac vessels was observed at multiple lumbar levels.
• Symmetric AP excursion of the psoas major muscle was noted at L2-L3 and L4-L5 in the prone position.
• No significant differences in mean translation were found across different lumbar levels.

Conclusions:

• Prone positioning causes measurable anterior translation of the psoas major muscle and great vessels.
• These positional anatomical changes can alter the operative corridor for PTP LLIF.
• Accounting for these discrepancies is essential to minimize neurovascular risk during PTP LLIF.