Recognizing the Hourglass/Bow-Tie Pattern
I read with keen interest the article by Desmet et al,1 “A Longitudinal Supra-Inguinal Fascia Iliaca Compartment Block Reduces Morphine Consumption After Total Hip Arthroplasty.” I would like to highlight the lacunae in their block performance technique. The authors mention 38% patients have unclear demarcation of fascia iliaca1 and the underlying muscles, which would not be acceptable for block performance. The explanation of the correct technique would improve the pattern recognition and the success rate of the block.
In their Figure 1, the authors have shown bow-tie sign over the anterior superior iliac spine, which is anatomically not correct. The pattern recognition shown in their Figure 1 can only be seen superior to anterior inferior iliac spine.
A simplified technique for suprainguinal fascia iliaca block has been described previously by Singh and Jones.2 It involves placing the probe longitudinally on the anterior superior iliac spine, pointing midway between the xiphisternum and the umbilicus. The probe is moved medially along the inguinal ligament, maintaining the same angulation until the hourglass/bow-tie pattern is reached (Figs. 1, 2). The lateral part of the hourglass is the sartorius muscle and the medial part being the internal oblique. The hourglass is superficial to the iliacus muscle, and injecting local anesthetic between the iliacus and internal oblique will give the best results. The characteristic feature is that the midpoint of hourglass is always superficial to anterior inferior iliac spine, which helps in improving pattern recognition and demarcation of fascia.