Ultrasound assessment of the vertebral level of the palpated intercristal (Tuffier's) line.

Purpose: Identification of a particular vertebral level by clinical landmark palpation is inaccurate. This study uses ultrasound imaging to assess the vertebral level at which the palpated intercristal line occurs in subjects clinically positioned to receive a neuraxial technique.

Methods: Following Research Ethics Board approval and informed written consent, 114 adult subjects were seated in the position used clinically for placement of a neuraxial block. A single investigator marked the skin where the palpated intercristal line crossed the spinous processes. A 2-5 MHz curved ultrasound probe in paramedian orientation was advanced cephalad from the sacrum, counting the ultrasound-visualized intervertebral levels until the skin marking was encountered. The weight, height, waist circumference, body mass index, and age of the volunteers were recorded. These physical characteristics and relationship to the ultrasound-measured palpated intercristal line were assessed using the Chi square and Tukey Honestly Statistically Different tests.

Results: Using ultrasound, the palpated intercristal line was identified at the L3-4 interspace in 83 (73%), at L4-5 in 16 (14%), and at L2-3 in 15 (13%) of volunteers, respectively. Those with a palpated intercristal line at L2-3 were taller (mean difference 7.8 cm, 95% confidence interval 2.6-13.0 cm) and more likely to be male (22% vs 6%; P = 0.016) than those imaged with a palpated intercristal line at L3-4 or below.

Conclusions: According to ultrasound, the palpated intercristal line falls at the L3-4 interspace, or below, in the majority of subjects positioned for neuraxial block in the sitting position. A palpated intercristal line at L2-3 was more likely in tall and male individuals.