A 26-year-old man sustains a right posterior hip dislocation in a dashboard injury. Closed reduction is performed within 2 hours. He now has inability to dorsiflex the ankle and numbness over the dorsum of the foot, but plantar flexion is strong. Which structure is injured?

• A Superior gluteal nerve at the greater sciatic notch
• B Tibial division of the sciatic nerve in the popliteal fossa
• C Deep branch of the common peroneal division of the sciatic nerve ✓
• D Lumbosacral trunk stretched against the sacral ala

Explanation

The sciatic nerve is injured in roughly 10 percent of posterior hip dislocations, and the peroneal division is preferentially affected because its fibers lie posterolateral and have less tensile strength. Isolated loss of dorsiflexion with preserved plantar flexion localizes the lesion to the deep peroneal branch, giving a foot drop. The tibial division supplies plantar flexion, which remains intact here.

Reference: Rockwood and Green's Fractures in Adults, 9th ed.

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Written and medically reviewed by the StethoPrep medical team.