The intercristal line determined by palpation is not a reliable anatomical landmark for neuraxial anesthesia

The radiological intercristal line (Tuffier's line) usually intersects the spine at the L4-L5 interspace. The intercristal line determined by palpation may be used erroneously as a surrogate for the true radiological Tuffier's line. We studied term pregnant women to establish the level at which a transverse line connecting the superior aspects of the iliac crests, as determined by palpation, intersects the lumbar spine, as assessed by ultrasound.

Term pregnant women were recruited, with the exception of those with scoliosis or previous spinal surgery. With the subjects in the sitting position, the attending anesthesiologist palpated and marked the superior aspects of the iliac crests bilaterally. One of the investigators, blinded to the markings, performed a lumbar spine ultrasound scan to identify the lumbar interspaces. Each interspace was marked on the patient's back. The bilateral markings were then revealed, and a line connecting them was drawn on the patient's back. This line and the markings of the interspace levels were plotted on a transparent sheet.

Forty-five women were studied. The palpated intercristal line was located above the L4-L5 interspace in all of the women. The median level of intersection was immediately below the L2-L3 interspace, with a range from immediately above L1-L2 to immediately above L4-L5. There was a low positive correlation between the level of intersection and the body mass index (r = 0.32; P = 0.03).

In pregnant women at term, the intercristal line determined by palpation does not correspond to the Tuffier's line determined radiologically, and it may intersect the spine at up to three interspaces higher.