Teaching Case

A 42-year-old male with no comorbidities presented with complaints of pain on the medial aspect of the left ankle, cramps on the left leg during the night and numbness of the left first to third toes for 4 weeks.

On clinical examination, he had normal power of intrinsic foot muscles with normal sensation. Tinel’s sign was positive in the left tarsal tunnel region along with tenderness.

MRI of the left ankle shows a lobulated mass along the medial aspect of the calcaneus (arrow), demonstrating fluid signal intensity on fat-suppressed T2-weighted sagittal (Figure 1a) and coronal (Figure 1b) images and T2-weighted sagittal image (Figure 1d). The mass demonstrated an iso to hypointense signal intensity to skeletal muscle on T1-weighted images (Figure 1c) along the medial aspect of the calcaneum posterior to the flexor digitorum longus tendon.

Ultrasound of the left ankle shows a lobulated cystic lesion behind the medial malleolus (Figure 2).

Background

The tarsal tunnel is a fibro-osseous channel extending from the ankle to the midfoot, through which the medial tendons and the posterior tibial neurovascular bundle pass. Tarsal tunnel syndrome (TTS) is a compression neuropathy of the posterior tibial nerve or one of its branches and may be caused by a variety of pathologic lesions [1].

The aetiology can be intrinsic or extrinsic:

• Extrinsic causes include poorly fitting shoes, trauma, anatomic-biomechanical abnormalities (tarsal coalition, valgus or varus hindfoot), post-surgical scarring, systemic diseases, generalised lower extremity oedema, systemic inflammatory arthropathies, diabetes, and post-surgical scarring.
• Intrinsic causes include tendinopathy, tenosynovitis, perineural fibrosis, osteophytes, hypertrophic retinaculum, and space-occupying or mass effect lesions (enlarged or varicose veins, ganglion cyst, lipoma, neoplasm, and neuroma). Arterial insufficiency can lead to nerve ischemia [3].

Clinical Perspective

Symptoms include sole numbness, pain, and a cold sensation; they affect the patient’s quality of life [2]. TTS can present similarly to other lower extremity conditions, with the most common differential diagnosis being plantar fasciitis, as these patients also present with plantar heel pain. In addition to plantar fasciitis (in which TTS is thought to be commonly misdiagnosed), polyneuropathy, L5 and S1 nerve root syndromes, Morton’s metatarsalgia, compartment syndrome of the deep flexor compartment will have to be distinguished from tarsal tunnel syndrome as well [4].

Imaging Perspective

Imaging, in particular MRI, can help identify causative factors in individuals with suspected TTS and help aid surgical management. The detection of a space-occupying lesion is important, as surgery is advised.

Outcome

Treatment of tarsal tunnel syndrome is initially conservative and includes behavioural modification, physical therapy, immobilisation, and anti-inflammatory medication. Surgical release of the flexor retinaculum and removal of the offending mechanism is attempted in refractory cases or in cases with mass effect, but results vary depending on the aetiology, duration of symptoms, and the age of the patient. The longer the duration of symptoms and the older the patient, the worse the prognosis.

Take Home Message / Teaching Points

• To consider tarsal tunnel syndrome in paraesthesia of the foot.
• There is no best test to diagnose tarsal tunnel syndrome, and it is a combination of history, examination, imaging, electromyography and nerve conduction studies.

Written informed patient consent for publication has been obtained.