A Dynamic Test to Identify the Potential Recess Between the Psoas Major and Quadratus Lumborum Muscles at the Supra-Iliac Level

PURPOSE: The transmuscular quadratus lumborum block (TQLB) deposits the local anesthetic into the fascial interspace between the quadratus lumborum (QL) and psoas major (PM) muscles in the lumbar paravertebral regions. However, there are multiple anatomical relationships between the QL and PM muscles in the cross section of ultrasound scanning at the supra-iliac level, which may influence the identification of injection site with the TQLB. In the current study, we developed a dynamic test to identify the anatomical relationships between the QL and PM muscles. METHODS: Forty male and 40 female volunteers were enrolled from June 20, 2021 to July 2, 2021 at Beijing Chaoyang Hospital, Capital Medical University for this descriptive study. The ultrasound identification of the cross-section anatomical relationship between the QL and PM muscles was performed under the shamrock sonogram at the supra-iliac level. The types of anatomical relationship between the QL and PM muscles were divided into “separate” or “non-separate”. The volunteers who were identified as “non-separate” received the dynamic tests. The numbers of positive dynamic tests in “non-separate” volunteers were recorded. RESULTS: Six (15%) male volunteers and 10 (25%) female volunteers were identified as “separate”. Thirty-four male and 30 female volunteers who were identified as “non-separate” received the dynamic tests. The positive dynamic tests were observed in 8 (23.5%) male and 9 (30%) female volunteers, respectively. CONCLUSION: Our study showed that the potential recess between the encased QL and encased PM muscles may exist in “non-separate” subjects, in which the local anesthetic is injected may result in the block failure. A dynamic test could help distinguish the potential recess.