Tarsal tunnel syndrome caused by posterior facet talocalcaneal coalition: A case report.

Rationale: Tarsal tunnel syndrome (TTS) is a compressive neuropathy of the posterior tibial nerve and its branches. Tarsal coalition is defined as a fibrous, cartilaginous, or osseous bridging of 2 or more tarsal bones. TTS with tarsal coalition is uncommon. Here, we present a rare example of successful surgical management of TTS with posterior facet talocalcaneal coalition.

Patient Concerns: A 74-year-old woman presented with hypoesthesia, numbness, and an intermittent tingling sensation on the plantar area over the right forefoot to the middle foot area. The hypoesthesia and paresthesia of the right foot began 6 years previously and were severe along the lateral plantar aspect. The symptoms were mild at rest and increased during daily activities. Tinel sign was positive along the posteroinferior aspect of the medial malleolus.

Diagnosis: Lateral ankle radiography showed joint-space narrowing and sclerotic bony changes with a deformed C-sign and humpback sign. Oblique coronal and sagittal computed tomography revealed an irregular medial posterior facet, partial coalition, narrowing, and subcortical cyst formation of the posterior subtalar joint. Magnetic resonance imaging showed an abnormal posterior talocalcaneal coalition compressing the posterior tibia nerve. Electromyography and nerve conduction velocity studies were performed, and the findings indicated that there was an incomplete lesion of the right plantar nerve, especially of the lateral plantar nerve, around the ankle level.

Interventions: Surgical decompression was performed. Intraoperatively, the lateral plantar nerve exhibited fibrotic changes and tightening below the posterior facet talocalcaneal coalition. The coalition was excised, and the lateral plantar nerve was released with soft-tissue dissection.

Outcomes: The patient's symptoms of tingling sensation and hypoesthesia were almost relieved at 4 months postoperatively, but she complained of paresthesia with an itching sensation when the skin of the plantar area was touched. The paresthesia had disappeared almost completely at 8 months after surgery. She had no recurrence of symptoms at the 1-year follow-up.

Lessons: The TTS with tarsal coalition is rare. Supportive history and physical examination are essential for diagnosis. Plain radiographs and computed tomography or magnetic resonance imaging are helpful to determine the cause of TTS and verify the tarsal coalition. After diagnosis, surgical excision of the coalition may be appropriate for management with a good outcome.