BACKGROUND: This study was performed to evaluate the correlations between lumbar epidural depth by MRI and physical measurements.

METHODS: The anatomy of the lumbar epidural space was evaluated using MRI scans of 121 patients (93 male and 31 female). Epidural depth was measured from the skin to the center of the posterior epidural space at the L3-4 and L 4-5 levels by two methods (in a parallel line to the lumbar spinous process [SKEP I] and in a vertical line to the long axis of the spine [SKEP II]). Physical measurements such as weight, height, foot size, and waist were measured, other physical measurements such as the Ponderal index (PI), body mass index (BMI), and obesity (Broca's index) were calculated.

RESULTS: Significant correlations between depth from the skin to the posterior epidural space were found for Ponderal index (PI), body mass index (BMI), obesity (Broca's index), weight, waist circumference, height, and foot size. The depth from the skin to the supraspinous ligament correlated with BMI, obesity (Broca's index), PI, weight, and waist circumference. The depth from the supraspinous ligament to the posterior epidural space were found to correlate with height and foot size.

CONCLUSIONS: PI had a higher predictive value for epidural depth than the other physical measurements.