A patient injures the femoral nerve at the level of the inguinal ligament. Which functional deficit would be ABSENT in this lesion, distinguishing it from a lumbar plexus lesion at L2–L4?

• A Loss of knee extension
• B Loss of adduction of the thigh ✓
• C Loss of hip flexion (iliopsoas)
• D Absent knee jerk reflex

Explanation

Thigh adduction is performed by the adductor muscles (adductor longus, brevis, and magnus, gracilis, pectineus), which are innervated by the obturator nerve (L2–L4) — not the femoral nerve. An isolated femoral nerve lesion at the inguinal ligament causes weakness of knee extension (quadriceps), weakness of hip flexion (iliopsoas branch arises proximal to or just under the inguinal ligament), and loss of the knee jerk reflex, but adduction is completely preserved because the obturator nerve takes a separate path through the obturator foramen.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.