During a difficult forceps delivery, a mother develops inability to abduct her left thigh against resistance, along with sensory loss over the medial thigh. She reports the problem began immediately after delivery. Which nerve is injured and by what mechanism?

• A Sciatic nerve compressed against the ischial spine by the fetal head
• B Femoral nerve compressed at the inguinal ligament
• C Obturator nerve compressed against the lateral pelvic wall by the fetal head or forceps blade ✓
• D Lumbosacral trunk compressed against the sacral ala

Explanation

Obturator nerve palsy during difficult delivery or prolonged labor occurs when the fetal head or forceps compresses the nerve against the lateral pelvic wall as it passes through the obturator canal. Loss of adductor function (hip adduction) and medial thigh sensation are characteristic. The lumbosacral trunk compression occurs at the pelvic brim against the sacral ala and produces foot drop (L4,5 contribution to common peroneal nerve). Femoral nerve injury during gynecological procedures results from extreme hip flexion/abduction with retractor pressure.

Reference: BD Chaurasia's Human Anatomy, 8th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.