Prone Position for Preoperative Planning in Lumbar Endoscopic and Minimally Invasive Fusion Procedures: Insights From a Magnetic Resonance Imaging Study.

Background: Differences in lumbar morphology and nerve root positioning between supine and prone decubitus are poorly analyzed. This study aimed to perform a magnetic resonance imaging (MRI) study to describe lumbar morphology, nerve root, and related structures positioning in the prone position, while comparing with conventional supine MRI, in patients with lumbar symptoms. The second aim was to define safe working zones for lumbar surgical procedures.

Methods: This study was a prospective, single-center, observational study. Fifty patients with persistent low back and/or radicular pain that was unresponsive to conservative treatment were consecutively selected. Supine and prone 3 Tesla MRIs were performed. Two independent researchers performed an imaging analysis of predefined variables.

Results: Lumbar lordosis significantly changed from 49.3° in the supine position to 52.1° in the prone position (P = 0.005), without a statistically significant difference in lower lumbar lordosis. No consistent changes were found regarding foraminal height, root-to-pedicle or root-to-superior articular process distances. The exiting nerve root was found between 42% and 49% of the foraminal height (as measured from the upper border of the lower pedicle). The left retroperitoneal lateral corridor showed no significant size variation from the supine to the prone position (P = 0.196 and P = 0.600, for L3-L4 and L4-L5 levels, respectively).

Conclusion: This study suggests prone positioning may increase global lumbar lordosis, without changing the position of other major anatomical structures. The exiting nerve root positioning can be estimated in relation to foraminal height. These finding may help optimizing planning and minimizing iatrogenic lesions.

Level of evidence: 3: