The tarsal tunnel is an anatomical structure located on the medial side of the ankle where the foot joins the lower leg. Specifically, it is located posterior and inferior to the medial malleolus. Unlike the carpal tunnel of the wrist, which is oriented horizontally and has an osseous floor and fibrous roof, the tarsal tunnel is oriented vertically. The osseous lateral portion of the tunnel is formed by the medial malleolus anteroposteriorly and the posterior talus and calcaneus bones laterally. A fibrous flexor retinaculum extending from the medial malleolus to the medial calcaneus forms the medial border of the tarsal tunnel. This structure holds the contents of the tarsal tunnel up against the bone, preventing medial displacement.
Similar to the carpal tunnel of the wrist, the tarsal tunnel serves as an important passageway for several structures. These include the tendons of the tibialis posterior, flexor digitorum longus (FDL), and flexor hallucis longus (FHL). Running alongside these three tendons are the posterior tibial nerve, artery, and vein. Organized from medial to lateral, the contents of the tarsal tunnel are the tibialis posterior tendon, FDL tendon, posterior tibial artery and vein, posterior tibial nerve, and FHL tendon. The posterior tibial nerve bifurcates within the tarsal tunnel (most common) or just proximal to it (less common) into the medial and lateral plantar nerves.
Both the medial plantar nerve and lateral plantar nerve have both sensory and motor fibers in the foot. Sensory function for the medial plantar nerve includes the medial half of the foot, the first three digits, and half of the fourth. Motor function includes the lumbricals, abductor hallucis, flexor digitorum brevis, and flexor hallucis brevis. Sensory function for the lateral plantar nerve includes the medial calcaneus and lateral heel. Motor function includes the flexor digitorum brevis, quadratus plantae, and abductor digiti minimi.
As is the case with the carpal tunnel, space within the tarsal tunnel is relatively limited with very little capacity for expansion. This space can be further restricted by both extrinsic and intrinsic factors. Extrinsic factors (restricting forces from outside the tunnel) include improperly fitted shoes, generalized edema from trauma or chronic conditions, posttraumatic or postsurgical scarring, and postural or anatomical abnormalities such as pes planus. Intrinsic factors (restricting forces within the tunnel) include tendinopathy, tenosynovitis, osteophytes, soft-tissue fibrosis, and space-occupying etiologies like ganglion cysts, varicose veins, lipomas, or tumors. All these factors can create compression of the posterior tibial nerve, medial plantar nerve, or lateral plantar nerve within the tarsal tunnel.
Nerve compression within the tarsal tunnel is referred to as tarsal tunnel syndrome or posterior tibial neuralgia and presents as burning pain or numbness in the associated area that occurs spontaneously or with movement and/or weakness or atrophy in the associated muscles. As is the case with carpal tunnel syndrome, nerve dysfunction is often progressive and can become permanent if left untreated. It can be more challenging to treat the tarsal tunnel as it is an integral part of the weight-bearing architecture of the lower extremity and significantly less common than carpal tunnel syndrome. A comprehensive assessment of both extrinsic and intrinsic factors is required in order to determine proper treatment.
Tarsal Tunnel
Borders
• Medial: Flexor retinaculum
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Lateral: Medial malleolus (anterosuperior)
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Posterior: Talus and calcaneus (lateral)
Contents
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Tendons: Tibialis posterior, flexor digitorum longus, and flexor hallucis longus
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Nerve: Posterior tibial nerve
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Blood Supply: Posterior tibial artery and vein
Continue moving posteriorly and inferiorly into the trough at the medial calcaneus.
Repeat as you pin the flexor tendons in various directions.
Christy Cael is a licensed massage therapist and certified strength and conditioning specialist. Her private practice focuses on injury treatment, biomechanical analysis, craniosacral therapy, and massage for clients with neurological issues. She is the author of Functional Anatomy: Musculoskeletal Anatomy, Kinesiology, and Palpation for Manual Therapists (New York: Jones & Bartlett Learning, 2010; jblearning.com). Contact her at christy_cael@hotmail.com.