A 40-year-old male runner presents with acute-onset posterior heel pain during a sprint; he felt a 'pop' and now has significant weakness of plantarflexion. The Thompson test is positive. The most reliable clinical sign distinguishing complete Achilles tendon rupture from partial tear is:

• A Positive Thompson (Simmonds) test — absent plantarflexion on calf squeeze — confirming complete rupture ✓
• B Inability to walk on tiptoe — this reliably confirms complete rupture
• C Severe pain on palpation of the Achilles tendon
• D Swelling and bruising of the ankle

Explanation

The Thompson (Simmonds) test is performed with the patient prone; squeezing the calf should produce passive plantarflexion if the tendon is intact. A positive test (absent plantarflexion response) is highly sensitive (~96%) and specific for complete Achilles tendon rupture. Walking on tiptoe can still be achieved in complete rupture because toe-standing can be maintained by flexor hallucis longus and peronei — making this test unreliable for distinguishing complete from partial rupture. Pain and swelling are non-specific. MRI is confirmatory for partial tears where the clinical diagnosis is equivocal.

Reference: Maheshwari Essential Orthopaedics, 6th ed.

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Written and medically reviewed by the StethoPrep medical team.