Corpus: Obturator nerve

The obturator nerve originates from the lumbar plexus, specifically from segments L2 to L4. It is composed of both general somatosensory fibers, which transmit sensory information, and somatomotor fibers, which control muscle movement.

This nerve initially courses within the pelvis, positioned medially to the psoas major muscle and proximate to the ovary. It then traverses beneath the vasa iliaca and proceeds through the obturator canal, lying dorsal to the pectineus muscle as it enters the medial thigh. Above the adductor brevis muscle, the obturator nerve bifurcates into two terminal branches: the anterior and the posterior branches. These branches continue their paths anteriorly and posteriorly relative to the adductor brevis muscle, respectively.

3.1. Anterior branch

The anterior branch innervates the following muscles:

• Adductor brevis muscle (may also be innervated by the posterior branch as a variant)
• Adductor longus muscle
• Gracilis muscle
• Pectineus muscle (jointly with the femoral nerve)

The cutaneous fibers of the anterior branch provides sensory innervation to a small area of the medial thigh.

3.2. Posterior branch

The posterior branch innervates the following muscles:

• External obturator muscle
• Adductor magnus muscle (jointly with the tibial nerve)

The posterior branch also provides sensory fibers to the knee joint.

4.1. Gynaecology

The obturator nerve runs lateral to the ovary. Consequently, conditions such as ovaritis or ovarian carcinoma may cause pain to radiate to the medial side of the thigh and knee. This pain, associated with irritation of the sensitive areas of the obturator nerve, is referred to as the Romberg knee phenomenon.

4.2. Urology

The obturator nerve's proximity to the posterior wall of the bladder makes it susceptible to irritation during transurethral resections of the bladder, particularly when monopolar resection instruments are used. This irritation can cause involuntary adduction of the hip joint. In adverse scenarios, this movement may result in perforation of the bladder wall. Therefore, an obturator nerve block is recommended during transurethral resections (TUR) of the bladder that involve the posterior wall.