Flexor retinaculum of the foot

The flexor retinaculum of the foot (retinaculum musculorum flexorum pedis) is a fibrous band located on the medial aspect of the ankle, extending from the medial malleolus to the calcaneus. It functions to secure the flexor tendons, tibial nerve, and posterior tibial artery as they pass into the foot.

Anatomy

The flexor retinaculum is a thick connective tissue structure that spans:

• Superiorly: From the medial malleolus of the tibia.
• Inferiorly: To the medial surface of the calcaneus.
• Laterally: Forms the roof of the tarsal tunnel.

Contents of the Tarsal Tunnel

The flexor retinaculum forms the tarsal tunnel, a passage for important structures into the foot. These structures, from anterior to posterior, are:

1. Tibialis posterior tendon (Tibialis posterior)
2. Flexor digitorum longus tendon (Flexor digitorum longus)
3. Posterior tibial artery and posterior tibial vein (Posterior tibial artery)
4. Tibial nerve (Tibial nerve)
5. Flexor hallucis longus tendon (Flexor hallucis longus)

A common mnemonic for these structures is: "Tom, Dick, And Nervous Harry":

• T – *Tibialis posterior tendon*
• D – *Flexor Digitorum longus tendon*
• A – *Artery (Posterior tibial artery)*
• N – *Nerve (Tibial nerve)*
• H – *Flexor Hallucis longus tendon*

Function

The flexor retinaculum of the foot:

• Holds the flexor tendons in place, preventing "bowstringing" during movement.
• Protects the neurovascular structures passing through the tarsal tunnel.
• Maintains the arch of the foot by supporting tendon function.

Clinical Significance

Tarsal Tunnel Syndrome

Compression of the tibial nerve under the flexor retinaculum leads to tarsal tunnel syndrome, characterized by:

• Pain and numbness along the medial foot.
• Tingling (paresthesia) in the sole of the foot.
• Weakness of intrinsic foot muscles in severe cases.

Treatment includes:

• Rest and activity modification
• Orthotic support to reduce compression
• Corticosteroid injections
• Surgical release (tarsal tunnel release) in resistant cases

Related Structures

• Flexor retinaculum of the hand (Transverse carpal ligament)
• Extensor retinaculum of the foot (Extensor retinaculum of the foot)
• Plantar aponeurosis (Plantar fascia)
• Medial malleolus (Tibia)
• Calcaneus (Heel bone)

See Also

• Tarsal tunnel syndrome
• Tibial nerve
• Posterior tibial artery
• Flexor digitorum longus
• Flexor hallucis longus