Chapter 144. Obturator Nerve Block

Anatomy (Figures 144-1 and 144-2):

• Branch of the lumbar plexus (L2–L4)
• Typically emerges from the medial border of the psoas muscle at the level of the pelvic brim, and divides in the obturator canal into anterior and posterior branches, although variations are common with a multiple branching pattern
• The anterior branch gives an articular branch to the hip joint, provides motor innervation of the adductor brevis, adductor longus, gracilis, and occasionally the pectineus (usually femoral nerve), and innervates a variable area of skin; most sources show an area in the medial aspect of the thigh, while others suggest a more distal location at the level of the knee. Sensory testing is thus unreliable
• The posterior branch provides motor innervation to the adductor magnus, obturator externus, and occasionally the adductor brevis (in that case, this muscle is not innervated by the anterior branch), and ends with an articular branch to the knee joint

Indications:

• Supplementation of femoral and sciatic nerve blocks for lower extremity surgery, especially knee surgery
• Prevention of the obturator reflex during transurethral resection of the bladder (TURB). The reflex is due to the stimulation through the bladder of the obturator nerve, resulting in sudden thigh adduction that can cause bladder perforation. Bilateral blocks have to be performed to be effective

Contraindications:

None specific.

Technique using NS:

• Labat's original technique is uncomfortable for the patient, as it requires bone contact and multiple redirecting of the needle, and the needle may enter the pelvis if inserted too far
• The technique ...