A 62-year-old man presents with acute onset foot drop and inability to dorsiflex the foot. Examination reveals weakness of ankle dorsiflexion and toe extension, with sensory loss over the dorsum of the foot and first web space. Which is the most common site of compression of the nerve causing these findings?

## Clinical Presentation Analysis The patient presents with classic deep peroneal nerve (common peroneal nerve) palsy: foot drop, weakness of ankle dorsiflexion and toe extension, and sensory loss in the first web space. ## Most Common Site of Compression **Key Point:** The fibular head is the most common site of compression of the common peroneal nerve, accounting for approximately 40–50% of all peroneal nerve palsies. ### Anatomical Basis The common peroneal nerve is a terminal branch of the sciatic nerve that: 1. Diverges from the tibial nerve in the popliteal fossa 2. Winds laterally around the **neck of the fibula** just below the fibular head 3. Pierces the peroneus longus muscle to enter the anterior compartment At the fibular head, the nerve is superficial and vulnerable to: - Direct trauma (blow to lateral knee) - Prolonged pressure (crossed legs, tight casts, prolonged squatting) - Traction injury - Fracture of the fibular neck ## Comparative Sites of Compression | Site | Frequency | Clinical Context | Nerve Affected | |------|-----------|------------------|----------------| | **Fibular head** | **Most common (40–50%)** | **Trauma, pressure, fracture** | **Common peroneal nerve** | | Piriformis muscle | Rare (< 5%) | Piriformis syndrome | Sciatic nerve (proximal) | | Popliteal fossa | Uncommon (10–15%) | Baker's cyst, trauma | Sciatic branches | | Sciatic notch | Rare (< 5%) | Pelvic pathology, injection injury | Sciatic nerve (proximal) | **High-Yield:** The common peroneal nerve's superficial course around the fibular neck makes it the most vulnerable point in the entire sciatic nerve distribution. ## Clinical Pearl The "Saturday night palsy" classically results from compression at the fibular head when a person falls asleep with the leg draped over a chair or bench, causing pressure on the lateral knee. ## Mnemonic **FIBULAR HEAD = Most Vulnerable:** - **F**ibular head: superficial, unprotected - **I**njury-prone: trauma, pressure, fracture - **B**ranch point: divergence from sciatic nerve - **U**nlike proximal sites: more accessible to external compression - **L**ateral position: exposed to lateral knee trauma - **A**natomically critical: narrow space for nerve passage - **R**arely spared: in common peroneal palsies [cite:Standring Anatomy 42e Ch 60]