**4. Quadratus lumborum block muscle**

### **4.1 Anatomy**

The quadratus lumborum muscle is part of the posterior abdominal wall and is located dorsal to the iliopsoas muscle. It has its origin in the posteromedial iliac crest in the iliolumbar ligament, and it inserts on the medial border of the twelfth rib (T12) and in the transverse processes of the first and fourth lumbar vertebrae (L1–L4), in the medial third of the iliac crest. Posterior to the quadratus lumborum muscle is the erector spinae muscle group, which consists of the multifidus, longissimus, and iliocostalis (**Figure 5**) [21–23].

The ventral branches of the spinal nerves (including the subcostal and iliohypogastric nerves) run between the quadratus lumborum muscle and its anterior fascia (**Figure 6**).

#### **Figure 5.**

*Quadratus lumborum block. Anatomical concepts, mechanisms, and techniques. (A) A posterior diagram illustration of the musculature of the posterior abdominal wall. The quadratus lumborum muscle originates from medial border of the twelfth rib and lumbar vertebrae transverse processes and inserts into the posteromedial iliac crest. (B) An anterior schematic illustration of the musculature of the posterior abdominal wall. On the left, the psoas muscle has been removed to reveal the ventral rami of the spinal nerve roots and branches passing anterior to the quadratus lumborum muscle. ES, erector spinae; LD; latissimus dorsi; QL, quadratus lumborum; TP, transverse process (Cleveland Clinic Center for Medical Art & Photography © 2018).*

#### *Ultrasound-Guided Regional Analgesia for Post-Cesarean Pain DOI: http://dx.doi.org/10.5772/intechopen.101465*

#### **Figure 6.**

*A schematic illustration of cross-section at L4 level showing the quadratus lumborum muscle with the different layers of the thoracolumbar fascia. On the left, the two-layer model is depicted, where the purple dashed line represents the anterior layer of the thoracolumbar fascia, and the green dashed line represents the transversalis fascia. On the right, the three-layer model is depicted, where the purple dashed line represents the middle layer of the thoracolumbar fascia, and the green dashed line represents the anterior layer of the thoracolumbar fascia. The blue dashed line represents the posterior thoracolumbar fascia. IL, iliocostalis; LD, latissimus dorsi; Lo, longissimus; Mu, multifidus; PM, psoas major; QL, quadratus lumborum; TLF, thoracolumbar fascia. Reprinted with permission, Cleveland Clinic Center for Medical Art & Photography © 2018. All Rights Reserved. showing the quadratus lumborum muscle with the different layers of the thoracolumbar fascia.*

The quadratus lumborum muscle is surrounded by the thoracolumbar fascia (FTL) that comprises the multilayer fascia and aponeurosis with the two proposed models [21–23]:


Knowledge of the anatomy of the thoracolumbar anterior fascia is important to understand the propagation after administration of the local anesthetic. The transverse fascia is divided into two layers: the inner layer that continues with the endothoracic and allows a cephalic spread of the local anesthetic (thoracic paravertebral space), and the outer layer that mixes with the arcuate ligaments of the diaphragm [21, 23, 24]. The abdominal aorta gives rise to the lumbar arteries from which the abdominal branches emerge, and these run lateral and posterior to the quadratus lumborum muscle.

#### *4.1.1 Neurovasculature*

On the ventral aspect of the quadratus lumborum muscle are the iliohypogastric, ilioinguinal, and subcostal nerves enveloped by the transversalis fascia. The sensory dermatome level involves T12–L2. There may be spread to the lateral femoral cutaneous nerve, the obturator, and the femoral nerve within the psoas (L4 and L5). On the dorsal aspect of the quadratus lumborum plane are the dorsal branches of the spinal nerves

that innervate the erector spinae muscle and the sympathetic nerve fibers that innervate the muscles of the abdomen and innervate the thoracolumbar fascia [21–23].
