Common or posterior obturator nerve block:

– analgesia after total knee alloplasty combined with saphenous nerve block

Common or anterior obturator nerve block:

– anaesthesia of the adductor muscles

– supplementary preoperative analgesia for hip fracture patients if a femoral nerve
block is not sufficient

The obturator nerve origins from the spinal nerve roots L2-L4 of the lumbar plexus. It descends along the medial side of the psoas major in the lumbar paravertebral space, runs across the sacral ala and enters the lesser pelvis and the obturator canal along with the obturator artery and vein.

It innervates the external obturator and splits into an anterior and a posterior branch that run anterior and posterior to the adductor brevis respectively.

The anterior branch innervates the adductor longus, adductor brevis, gracilis and pectineus. And a variable small skin area on the medial side of thigh. The pectineus is also innervated by the femoral nerve. The medial part of the hip joint is innervated by the anterior branch or the common obturator nerve.

The posterior branch innervates the adductor magnus. The adductor magnus is also innervated by the sciatic nerve. The posterior branch descends through the adductor hiatus and innervates the posterior part of the knee capsule. The cruciate ligaments of the knee are innervated by the terminal posterior branch.

The lateral femoral cutaneous (LFC) nerve is sandwiched between the fascia lata and the sartorius fascia a short distance approx. 3 cm below the ASIS, before the LFC nerve (or its two branches) pierces the fascia lata and innervates the lateral thigh

Often it is not possible to visualize the LFC nerve between the two fascia on top of the sartorius

The lateral femoral cutaneous nerve innervates the lateral thigh from the major trochanter to the knee

Place the patient supine

Place the high-frequency linear probe in the axial plane across the sartorius muscle approximately 3 cm below the anterior superior iliac spine

Visualize the sartorius fascia and the fascia lata with a shallow image depth (see next page)

Insert the needle with in-plane technique from the lateral end of the probe and advance the needle tip between the fascia lata and the sartorius fascia. Inject 5-10 mL of local anaesthetic

The needle is advanced through the fascia lata and the iliaca fascia – but not into the muscle

Local anaesthetic is injected into the fascial plane between the iliaca fascia and the muscle

Cutaneous analgesia of the lateral thigh

Skin harvesting

Postoperative analgesia after hip fracture surgery

The lateral femoral cutaneous (LFC) nerve emerges from the lateral margin of the psoas major and runs across the anterior surface of the iliacus below the iliacus fascia

Just medial to the anterior superior iliac spine (ASIS) the LFC nerve runs underneath the inguinal ligament, pierces the iliac fascia and runs obliquely across the sartorius muscle from medial to lateral sandwiched between the sartorius muscle fascia and the fascia lata

Approximately 2-3 cm below the ASIS, the LFC nerve pierces the fascia lata, splits in two branches and innervates the lateral thigh from the greater trochanter to the knee (see next page)

Dolan J, Williams A, Murney E, Smith M, Kenny GNC: Ultrasound guided fascia iliaca block: A comparison with the loss of resistance technique. Reg Anesth Pain Med 33: 526-531 (2008)

Hebbard P: Transversalis fascia plane block, a novel ultrasound-guided abdominal wall nerve block. Can J Anesth 56: 618-620 (2009)

Chin KJ, Chan V, Hebbard P, Tan JS, Harris M, Factor D: Ultrasound-guided transversalis fascia plane block provides analgesia for anterior iliac crest bone graft harvesting. Can J Anesth 59: 122-123 (2012)