Cutaneous branch of obturator nerve

The cutaneous branch of the obturator nerve is a variable and often limited branch of the obturator nerve that provides sensory innervation to the skin:

The anterior branch of obturator nerve leaves the pelvis in front of the Obturator externus and descends in front of the Adductor brevis, and behind the Pectineus and Adductor longus; at the lower border of the latter muscle it communicates with the anterior cutaneous and saphenous branches of the femoral nerve, forming a kind of plexus. Occasionally this communicating branch to the anterior cutaneous and saphenous branches of the femoral is continued down, as a cutaneous branch of obturator nerve, to the thigh and leg. When this is so, it emerges from beneath the lower border of the Adductor longus, descends along the posterior margin of the Sartorius to the medial side of the knee, where it pierces the deep fascia, communicates with the saphenous nerve, and is distributed to the skin of the tibial side of the leg as low down as its middle.

According to a cadaveric study, the cutaneous branch of the obturator nerve was found in 43% of cases, branching off the anterior ramus of the obturator nerve 6-10 cm distal to the inguinal ligament. When present, it innervates a 4-9 cm² area in the posteromedial popliteal fossa. [1]

Another study reported that the cutaneous branch can occasionally extend beyond the knee to the medial ankle and foot, although this is rare.[2] The variability in the presence and distribution of the cb-ar-ON makes clinical evaluation of obturator nerve block based on cutaneous anesthesia unreliable.[1]