Chapter 63

### INDICATIONS

The obturator nerve innervates a portion of the hip joint, most of the adductor muscles, a variable portion of the medial aspect of the femur, and has variable skin distribution on the medial aspect of the thigh.

• For acute and subacute pain

• Supplementation of femoral and sciatic nerve blocks for lower extremity surgery, especially knee surgery

• For refractory adductor spasms that interferes with acute rehabilitation

• For chronic pain

• As a diagnostic block for hip joint pain or for suspected neuropathy

• For chronic hip pain with a local anesthetic block, with or without steroids, or using radiofrequency lesioning

• For adductor spasticity as a neurolytic block. Kwon suggests that a selective blockade of the anterior branch may be sufficient to permit abduction more than 45 degrees.

• Another indication is to prevent 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.

### RELEVANT ANATOMY

• The obturator nerve is a mixed sensory and motor branch of the lumbar plexus and derives from the anterior divisions of the ventral rami of L2, L3, and L4 (Figure 63-1).

• It 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 (Figure 63-2), although variations are common with a multiple branching pattern.

• The anterior branch gives an articular branch to the hip joint (Figure 63-3), provides motor innervation of the adductor brevis, adductor longus, gracilis, and occasionally the pectineus, and innervates a variable area of skin; most references show an area in the medial aspect of the thigh, while others suggest a more distal location at the level of the knee.

• 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.

• The obturator nerve can be blocked with the other nerves of the lumbar plexus using the psoas compartment approach. Despite initial claims, a perivascular inguinal block (Winnie’s “3-in-1 block”) only rarely reaches the obturator nerve, as demonstrated by Macalou et al.

• The block can be performed using external anatomic landmarks and neurostimulation, or using imaging guidance (fluoroscopy or ultrasound, rarely CT scan). Blockade can be performed proximally, in the obturator foramen, before nerve division, or more distally, in the proximal thigh, between the adductor muscles.

• The anterior and posterior branches can be blocked separately at that level, as the anterior branch lies between adductor longus and adductor brevis, while the posterior branch lies between adductor brevis and adductor magnus.

###### Figure 63-1.

Anatomy of ...

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