Tarsal Tunnel Syndrome

Excerpt

Tarsal tunnel syndrome (TTS), sometimes referred to as "tibial nerve dysfunction" or "posterior tibial nerve neuralgia," is an entrapment neuropathy arising from the compression of the tarsal tunnel structures, particularly the posterior tibial nerve (see Image. Tarsal Tunnel Syndrome). This condition is often compared to carpal tunnel syndrome in the wrist, as both involve nerve compression in a confined space. However, TTS is much less common than carpal tunnel syndrome. The diagnosis is often clinical, though diagnostic tests may help identify a treatable source or rule out other serious conditions.

Anatomy of the Tarsal Tunnel

The tarsal tunnel is a narrow fibro-osseous space that runs posteroinferior to the medial malleolus (see Image. Tarsal Tunnel Anatomy). The tunnel's roof consists of the flexor retinaculum, passing from the medial malleolar tip to the medial calcaneal process and plantar aponeurosis. The floor comprises the medial surfaces of the tibia, talus, and calcaneus.

The tarsal tunnel houses multiple essential structures, including the following:

1. Tibialis posterior, flexor digitorum longus (FDL), and flexor hallucis longus (FHL) tendons

2. Posterior tibial artery and vein

3. Posterior tibial nerve (L4 to S3)

The orientation of these structures within the tarsal tunnel is noteworthy. The structures from medial to lateral are the tibialis posterior tendon, FDL tendon, posterior tibial artery and vein, posterior tibial nerve, and FHL tendon. Meanwhile, the structures from anterior to posterior are the tibialis posterior tendon, FDL tendon, posterior tibial neurovascular bundle (artery, vein, and nerve), and FHL tendon.

The posterior tibial nerve passes between the FDL and FHL muscles before it bifurcates in the tarsal tunnel, forming the medial and lateral plantar nerves. In 5% of people, the bifurcation occurs proximal to the tarsal tunnel.

The medial plantar nerve passes deep to the abductor hallucis and FHL muscles. This nerve has the following functions:

1. Provides afferents in the medial half of the foot

2. Provides afferents in the first 3 foot digits

3. Supplies efferents to the 1st lumbrical, abductor hallucis, flexor digitorum brevis, and flexor hallucis brevis

The lateral plantar nerve passes directly through the abductor hallucis muscle belly and has the following functions:

1. Provides afferents in the medial calcaneus

2. Supplies afferents in the lateral heel

3. Provides efferents in the flexor digitorum brevis, quadratus plantae, and abductor digiti minimi

The medial calcaneal nerve typically branches off the posterior tibial nerve proximal to the tarsal tunnel and provides sensory innervation to the posteromedial heel. This nerve diverges from the lateral plantar nerve or runs superficial to the flexor retinaculum in 25% of patients.