BACKGROUND: This study was performed to evaluate lumbar epidural depth using two methods, and to identify the correlation between epidural depth and body mass index (BMI).

METHODS: The anatomy of the lumbar epidural space was evaluated using MRI images in 124 patients (93 male and 31 female patients). Epidural depth was measured from the skin to the center of the posterior epidural space at the L3-4 and L4-5 level using two methods (in a parallel line to the lumbar spinous process [EP-I] and in a vertical line to the long axis of the spine [EP-II]).

RESULTS: The mean ± SD of epidural depth by EP-I was 4.82 ± 1.16 cm at L3-4 and 5.08 ± 1.08 cm at L4-5, and depth by EP-II was 4.18 ± 0.97 cm at L3-4 and 4.78 ± 1.02 cm at L4-5. The epidural depths were 3.71 to 4.37 cm (L3-4) and 4.36 to 4.65 cm (L4-5) in normal weight patients, 4.29 to 4.86 cm (L3-4) and 4.79 to 5.06 cm (L4-5) in overweight patients, and 5.16 to 5.87 cm (L3-4) and 5.79 to 6.16 cm (L4-5) in obese patients.

CONCLUSIONS: Epidural depth showed a close correlation with BMI, but not with sex.