Following an acetabular fracture, a patient develops inability to extend the knee, loss of sensation over the anterior thigh and medial leg, and absent knee jerk. The femoral nerve is injured. Where is the most likely site of injury?

• A Lumbar plexus within psoas muscle (L2-L4) ✓
• B Femoral triangle below the inguinal ligament
• C Adductor canal (Hunter's canal)
• D Lateral femoral cutaneous nerve at the ASIS

Explanation

The acetabulum's proximity to the posterior pelvic wall means an acetabular fracture can injure the femoral nerve at its origin within the substance of the psoas major (lumbar plexus, L2-L4). This level would cause complete femoral nerve deficit: paralysis of quadriceps (loss of knee extension), iliacus (impaired hip flexion), absent knee jerk, and sensory loss over the anterior thigh (medial and intermediate cutaneous nerves) and medial leg/foot (saphenous nerve). Femoral triangle injury is more commonly from penetrating trauma or groin procedures.

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

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.