Adducts the thigh and supplies sensation to the medial thigh
Mnemonic
“The obturator adducts”, from L2, L3 and L4:
- Motor - the adductor group: adductor longus, brevis and magnus (adductor part), gracilis, obturator externus
- Sensory - a small patch on the medial thigh
It passes through the obturator foramen and is the only nerve to do so, running along the lateral pelvic wall where it is vulnerable in pelvic surgery.
The referred pain pattern is the clinically useful part: the obturator nerve supplies both the hip joint and the medial thigh and knee, which is why hip pathology commonly presents as knee pain, particularly slipped upper femoral epiphysis in adolescents.
The obturator sign in appendicitis uses the same nerve: internal rotation of the flexed hip stretches obturator internus and reproduces pain when a pelvic appendix lies against it.
Obturator hernia compresses the nerve, giving the Howship-Romberg sign, medial thigh pain relieved by hip flexion, classically in thin elderly women.
Expansion
- Motor - the adductor muscles of the medial thigh (adductor longus, brevis and magnus, gracilis and obturator externus)
- Sensory - a patch of skin over the medial thigh
- Roots - L2 to L4
It enters the thigh through the obturator foramen, so a lesion weakens thigh adduction.