Tarsal Tunnel Exam

Tarsal Tunnel Syndrome (TTS) is a mononeuropathy caused by compression of the posterior tibial nerve or its branches in the foot/ankle [1]. TTS is analogous to Carpal Tunnel Syndrome, but occurs much more rarely, and usually as a result of trauma (fracture or sprain of the ankle), arthritis, or space-occupying lesions [2]. The tarsal tunnel runs deep to the flexor retinaculum of the ankle (connective tissue that connects medial malleolus with medial calcaneus), just posterior to the medial malleolus [2].

The clinical features of TTS are primarily paresthesia (tingling or pins and needles), hyperesthesia (increased sensitivity), and pain ranging from the posterior medial malleolar area to the sole, heel, and toes [2]. The symptoms may also radiate proximally up the calf, and typically worsen at night or with prolonged activity/ standing [2].

The tibial nerve arises from L4-S3 ventral divisions as part of the sciatic nerve and provides motor innervation to the posterior compartment of the leg, as well as sensory innervation to the foot and heel. The posterior tibial nerve gives off a branch to the medial calcaneus called the medial calcaneal nerve about 10cm proximal to the tarsal tunnel, supplying sensory innervation to the medial heel. Within the tarsal tunnel, the tibial nerve branches to form the lateral plantar nerve, medial plantar nerve, and the inferior calcaneal nerve, all of which can be compressed in tarsal tunnel syndrome. Notably, the inferior calcaneal nerve can be compressed in tarsal tunnel syndrome, leading to paresthesia and pain in the inferior heel, which often presents similarly to plantar fasciitis, a much more common condition.

The exam for tarsal tunnel syndrome begins with inspection of the medial malleolus and medial foot, looking for obvious deformities, masses, and overlying skin changes. Severe tarsal tunnel syndrome can cause atrophy of the intrinsic muscles of the foot, which are only rarely visualized on inspection. Special attention should be made for varicose veins, ganglion cysts, and bone spurs in the area as these can cause increased pressure in the tarsal tunnel. After inspecting, examiner should palpate the region carefully feeling for any obvious masses or tendon hypertrophy.

The lateral plantar nerve innervates the abductor digiti minimi muscle and the medial plantar nerve innervates the abductor hallucis muscle. These two muscles can atrophy and weaken from nerve compression at the tarsal tunnel. These muscles can be evaluated in tandem by asking the patient to splay their toes outwards and assessing the tension of the abductor hallucis and abductor digiti minimi muscles. The strength can subsequently be assessed by asking patient to abduct great toe and 5^th toe, and then resist examiner as examiner tries to adduct the great toe and 5^th toe, rating the strength on the MRC grading system of 0-5.

Strength Assessment of Abductor Hallucis and Abductor Digiti Minimi: Patient abducts great toe and 5^th toe, and then resists adduction from examiner squeezing toes together. Examiner can also use other hand to palpate muscle tension of the abductor hallucis and abductor digiti minimi.

Assess the sensory distribution of the tibial nerve using a rating system of 0 to 10, with 0 being no feeling at all and 10 being normal sensation. First, have patient close their eyes. Then, pick a location where patient has no complaints of sensory disturbances (like the shin) and lightly stroke the area with your finger, instructing the patient that if this sensation is 10 out of 10, please tell me from 0 (being no sensation at all) and 10 (being this sensation) how each of the following areas feel. Proceed to lightly stroke the plantar surface of the foot, noting regions of decreased or abnormal sensations.

Similar to carpal tunnel syndrome, symptoms of tarsal tunnel syndrome can be elicited with provocative maneuvers that aid in clinical evaluation.  

1.)   Nelson, Scott C. “Tarsal Tunnel Syndrome.” Clinics in podiatric medicine and surgery vol. 38,2 (2021): 131-141. doi:10.1016/j.cpm.2020.12.001

2.)   McSweeney, Simon C, and Matthew Cichero. “Tarsal tunnel syndrome-A narrative literature review.” Foot (Edinburgh, Scotland) vol. 25,4 (2015): 244-50. doi:10.1016/j.foot.2015.08.008

3.)   Schwieterman, Braun et al. “Diagnostic accuracy of physical examination tests of the ankle/foot complex: a systematic review.” International journal of sports physical therapyvol. 8,4 (2013): 416-26.

4.)   Merriman L, Turner W. Assessment of the lower limb. 2nd ed. London, UK: Churchill Livingstone; 2002.

5.)   Abouelela, Amr A K H, and Abeer K Zohiery. “The triple compression stress test for diagnosis of tarsal tunnel syndrome.” Foot (Edinburgh, Scotland) vol. 22,3 (2012): 146-9. doi:10.1016/j.foot.2012.02.002

6.)   Kinoshita, M et al. “The dorsiflexion-eversion test for diagnosis of tarsal tunnel syndrome.” The Journal of bone and joint surgery. American volume vol. 83,12 (2001): 1835-9. doi:10.2106/00004623-200112000-00011

7.)   Trepman, E et al. “Effect of foot and ankle position on tarsal tunnel compartment pressure.” Foot & ankle international vol. 20,11 (1999): 721-6. doi:10.1177/107110079902001108