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 level of the ankle joint on MRI, the structures you’re most concerned with are the extrinsic flexor tendons that cross the ankle. The flexor hallucis longus is the tendon that travels behind the medial malleolus and into the plantar foot to reach the distal phalanx of the big toe. Its position and course make it the structure you’re most likely to identify right at the ankle joint level on axial or sagittal images.

The flexor digitorum brevis is an intrinsic plantar muscle, residing in the sole of the foot, and does not appear at the ankle joint level on standard MRI slices. The flexor digitorum longus also crosses the ankle, but its tendon’s course is more anterior in the tarsal tunnel and it isn’t the structure most characteristically described at the ankle joint itself. Tibialis posterior is another tendon crossing the ankle, but the classic, easily identifiable flexor at the ankle joint level, especially behind the medial malleolus, is the flexor hallucis longus.