Following an acute injury, a patient has a clinically intact-appearing Achilles tendon and a negative Thompson (Simmonds) test despite a partial tear confirmed later on ultrasound. Which anatomical structure, if intact, is responsible for producing plantarflexion on calf squeeze and masking the injury?

• A Flexor hallucis longus tendon
• B Plantaris tendon ✓
• C Peroneus longus tendon
• D Tibialis anterior tendon

Explanation

The plantaris muscle runs alongside the Achilles tendon and inserts separately on the calcaneus. If the plantaris remains intact, squeezing the calf still produces some plantarflexion, giving a false-negative Thompson test in complete or high-grade Achilles ruptures. Flexor hallucis longus and peroneus longus contribute to plantarflexion but act at the toes and lateral column respectively and do not explain the calf squeeze response. Tibialis anterior is a dorsiflexor and would not produce plantarflexion on squeeze testing.

Reference: Gray's Anatomy for Students, 4th ed.

High-yield for: NEET PGINI-CETNExTFMGEUSMLEPLABMRCP

Written and medically reviewed by the StethoPrep medical team.