Quadratus lumborum (QL) block is a novel approach for managing postoperative pain in patients undergoing abdominal and hip surgeries.
The sensory dermatomal coverage of the QL block can extend from T7 to L2.
There is currently no general consensus on the mechanism of action of QL blockade.
This is a “tissue plane” block and thus requires a large volume of local anesthetic to obtain a reliable block.
The ultrasound probe is placed in the posterior axillary line between the iliac crest and the costal margin ( Fig. 38.1 ). The transversalis fascia (TF) covers the peritoneal surface of the transversus abdominis muscle and continues posteromedially covering the anterior side of the investing fascia of both the quadratus lumborum (QL) and psoas major (PM) muscles. The QL muscle is generally visualized as hypoechoic relative to the hyperechoic PM muscle located anteromedial to the QL muscle.
The QL muscle surrounded by the thoracolumbar fascia (TLF) is the target of the injection, not the muscle itself. The three-layered model of TLF is comprised of anterior, middle, and posterior layers. The posterior layer surrounds the erector spinae muscles; the middle-layer of the TLF passes between the erector spinae muscles and the QL muscle; and the anterior layer is thin and lies anterior to both the QL and PM muscles. The anterior layer of the TLF turns posterior between the QL and the psoas and attaches to the anterior aspect of each transverse process ( Fig. 38.2 ).
At the L3–L4 level, the transverse process of the third or fourth lumbar vertebrae, erector spinae muscle, PM muscle, and the QL muscle can be identified as the so-called “Shamrock sign”.
The external oblique muscle abuts the latissimus dorsi muscle. The internal oblique, with the transversus abdominis muscles, forms the aponeurosis of the middle thoracolumbar fascia (lateral raphe) posterior to the QL muscle ( Fig. 38.2 ).
Techniques ( fig. 38.3–38.8 )
Lateral QL (Previously referred as QL 1 block) The needle can be directed from anterior to posterior towards the junction of tapered transversus abdominis muscle and QL muscle; local anesthetic (LA) will then be deposited in the lateral border of QL muscle at the junction of the transversalis fascia and penetrate the aponeurotic attachment of the transversus abdominis muscle (lateral raphe) ( Fig. 38.3–38.4 ).