Which flexor muscle is at the level of the ankle joint on MRI?

Which flexor muscle is at the level of the ankle joint on MRI?

• A. Flexor Hallucis Longus
• B. Flexor Digitorum Longus
• C. Tibialis Posterior
• D. Flexor Digitorum Brevis

Answer: (A)

At the ankle level on MRI, the structure you would see crossing the joint is the tendon of the flexor hallucis longus. This tendon travels from the deep posterior compartment, passes behind the medial malleolus, and goes under the flexor retinaculum to reach the distal phalanx of the big toe. Its position and course make it the classic flexor tendon visible at the ankle joint level on axial images. The other options don’t cross the ankle in the same way: flexor digitorum longus also travels posterior to the ankle but toward the lesser toes, not directly across the ankle joint; flexor digitorum brevis is an intrinsic plantar muscle of the foot, not present at the ankle level; and tibialis posterior, while a deep posterior muscle/tendon behind the malleolus, does not occupy the same recognizable position crossing to a toe as the flexor hallucis longus.

At the ankle level on MRI, the structure you would see crossing the joint is the tendon of the flexor hallucis longus. This tendon travels from the deep posterior compartment, passes behind the medial malleolus, and goes under the flexor retinaculum to reach the distal phalanx of the big toe. Its position and course make it the classic flexor tendon visible at the ankle joint level on axial images.

The other options don’t cross the ankle in the same way: flexor digitorum longus also travels posterior to the ankle but toward the lesser toes, not directly across the ankle joint; flexor digitorum brevis is an intrinsic plantar muscle of the foot, not present at the ankle level; and tibialis posterior, while a deep posterior muscle/tendon behind the malleolus, does not occupy the same recognizable position crossing to a toe as the flexor hallucis longus.