BLOCK AT A GLANCE
Block of the obturator nerve at the inguinal crease.
Indications: Supplemental analgesia for hip and knee surgeries (considered as rescue block for knee surgery), prevention of thigh adduction response during transurethral bladder surgery, relief of painful or permanent hip adductor spasticity
Goal: Local anesthetic (LA) spread in the fascial planes containing the branches of the obturator nerve
Local anesthetic volume: 5 to 10 mL in each interfascial space or around each branch of the obturator nerve. For the proximal approach, use 10 to 15 mL.
The obturator nerve block is a well-established technique for hip and knee surgeries, traditionally performed based on landmarks and nerve stimulation. However, the anatomical variability and deep location of the structures make it difficult to achieve consistent results. The widespread availability of point-of-care ultrasound (US) led to a renewed interest in this technique because US allows visualization of the nerves and precise injection of LAs into the fascial planes through which they travel. Modifications of the technique have been proposed to optimize the spread of the injectate around the obturator nerve and along the obturator canal, proximal to the bifurcation of the nerve. The obturator nerve block may add to the quality of analgesia after hip and knee surgeries; however, its analgesic value in the context of a multimodal analgesia regime is yet to be determined.
Limitations and Specific Risks
A limitation of this technique includes the difficulty in obtaining good US images of the structures in the inguinal area. Likewise, the insufficient cranial spread of the LA and anatomical variability may result in an inconsistent block extent and limit the analgesic value to treat hip pain.
The risk of vascular puncture is a common complication related to this block because the obturator artery anastomoses with a branch of the medial circumflex femoral artery in the vicinity of the obturator nerve.
The obturator nerve arises from the ventral rami of the L2 to L4 lumbar nerves. It descends to the pelvis through the psoas major muscle emerging from its medial border, then travels posteriorly with the common iliac arteries and laterally along the pelvic wall toward the obturator foramen, through where it enters the thigh (Figure 27-1). In most individuals, the nerve divides before exiting the pelvis into an anterior and posterior branch, which are separated at first by fibers of the external obturator, and more distally by the adductor brevis muscles. The articular branches supplying the hip joint are usually derived from the common obturator nerve proximal to its division and only occasionally from the individual branches.
Anatomy of the obturator nerve in the thigh.
The anterior branch of the obturator nerve initially travels through the interfascial ...